Textile Dyeing Wastewater Treatment by Single and Intregated Processes of Coagulation, Chemical Oxidation and Biological Degradation

Textile Dy Integrated Processes of Coagulation, Chemical Oxidation and Carmen Susana de Deus Rodrigues Dissertation presented for the Ph.D. Degree in Environmental Engineering at the Faculty of Engineering, University of Porto, Portugal Laboratory of Separation and Reaction Engineering/ Laboratory for Process, Environmental and Energy Engineering Faculty of Engineering, University of Porto Textile Dy e ing Wastewater Treatment by Single and Integrated Processes of Coagulation, Chemical Oxidation and Biological Degradation Carmen Susana de Deus Rodrigues presented for the Ph.D. Degree in Environmental Engineering at the Faculty of Engineering, University of Porto, Portugal Supervisors Rui Alfredo da Rocha Boaventura Luís Miguel Palma Madeira Laboratory of Separation and Reaction Engineering/ Associated Laborat ory Laboratory for Process, Environmental and Energy Engineering (LEPAE) Chemical Engineering Department Faculty of Engineering, University of Porto Porto, September 2013 ing Wastewater Treatment by Single and Integrated Processes of Coagulation, Chemical Oxidation and presented for the Ph.D. Degree in Environmental Engineering at the Faculty of Rui Alfredo da Rocha Boaventura Madeira ory LSRE/LCM (LEPAE) i Acknowledgments To my supervisores, Doctor Rui Boaventura and Prof. Miguel Madeira, in part responsible for my interest in scientific research, I want to thank the opportunity to perform this work, as well as all the support, motivation, understanding and tremendous willingness over the years that we worked together. Also thanks for all suggestions, criticisms, compliments and encouragement to do more and better. I’m also grateful to all organizations and people without which this work would not have been possible: Fundação para a Ciência e a Tecnologia (FCT) for the PhD scholarship (SFRH/BD/46704/2008). Faculty of Engeneering, University of Porto (FEUP) and, particulary, the Laboratory of Separation and Reaction Engineering – LSRE, the Laboratory for Process, Environmental and Energy Engineering – LEPAE, and the Department of Chemical Engineering, for making available the resources and facilities to carry out this work. Erfoc - Acabamentos Têxteis S.A., namely Mr. Armando Amaro and Mr. Virgilio Guimarães, and DyStar (Porto), namely Mrs. Goretti Quinaz, for gently supplying the chemicals and dyes and the information required for effluents simulation. Textil Luís Simões, that provided a real effluent sample used in this study. Particularly I want to thank Mrs. Susana Costa for kindly receiving me, and for all the information and valuable assistance in collecting the effluent sample. Quimitécnica, namely Mr. Luís Quelhas, and Rivaz Química, for supplying the flocculants, as well as the prices of the chemicals used in this work. Mr. Claúdio Costa from Tratave and Mrs. Carla Azevedo from Rabada WWTP, for providing the biomass used in the degradation tests and in the acclimatization of the biological reactor . ii Prof. Fernando Pereira from the Laboratory of Catalysis and Materials (LCM) at FEUP for the help in establishing contact with the textile industry, as well as, in the last phase of the work, for the access to the Laboratory of Environmental Sciences. Professor Joaquim Faria and Doctor Claudia Silva from LCM at FEUP for kindly providing the actinometry data and supplying the mercury lamp TQ 150 for photo-Fenton experiments. Luís Carlos and Nuno Guereiro from the Departament of Chemical Engineering at FEUP for the promptness in solving some problems concerning the experimental setup of the Sequencing Batch Reactor (SBR) and the pilot plant of Fenton process . Doctor Salomé Soares from LCM, Mrs. Dionísia Portela from Centro Tecnológico das Indústrias Têxtil e do Vestuário de Portugal (CITEVE) and Mrs. Patrícia Alves for providing scientific literature, encouragement, sharing of knowledge, but rather by the friendship demonstrated since the 1st year of the graduation in Chemical Engineering. Doctor Nídia Caetano, Doctor Olga Freitas and Doctor Sónia Figueiredo from the Chemical Engineering Department, School of Engineering, Polytechnic Institute of Porto, for the friendship, encouragement and knowledge sharing. Liliana Pereira, Silvia Faia, Paula Pinheiro, Maria do Céu, Serafim Pereira, not only for providing the best working conditions at the Laboratory of Environmental Sciences, but also for the friendship, the precious help and the useful advices. I am also grateful to all people (so many that I cannot nominate all of them…) that I met at LSRE during this period of my life for the help, companionship and all the words of encouragement. Thanks to Filipa Duarte and Cátia Feliz from LEPAE for the very special friendship, companionship, help, conversations and confidences, and for all good time we spent together. Finally my eternal gratitude to my parents, my husband, my daughter, my brother, my sister, my sister in law and my niece, for the love, the unconditional support, the optimistic view of life and for making me a better person. iii Preface This PhD thesis was carried out at the Laboratory of Separation and Reaction Engineering, Associated Laboratory LSRE/LCM, and at the Laboratory for Process, Environmental and Energy Engineering (LEPAE) of the Department of Chemical Engineering, at the Faculty of Engineering – University of Porto. The thesis is structured into five parts divided in chapters with the following content: Part I – The background and motivation of this study are described in chapter 1, and the work to be performed in order to achieve the objectives is also referred to. A brief characterization of the textile sector in Portugal and the treatment technologies for this type of wastewater are also presented. Chapter 2 presents the state of the art of textile wastewater treatment by chemical coagulation/flocculation, advanced chemical oxidation with Fenton’s reagent, photo-Fenton process and biological oxidation in sequencing batch reactors (SBR). Parts II consists in one chapter (chapter 3) concerning the preparation of synthetic wastewaters and their characterization as well as the characterization of the textile industrial wastewater. The materials and methods used and the experimental procedures are also described. Part III is divided in 7 chapters presenting the experimental results obtained in the treatment of synthetic dyeing wastewaters either by single or combined processes. Part IV (Chapter 11) regards the treatment of a real cotton dyeing effluent by an integrated process of coagulation/flocculation plus Fenton’s oxidation, Fenton’s reagent alone and a combination of Fenton’s oxidation, coagulation/flocculation and biological degradation in SBR. Part V points out the main conclusions from this study and some suggestions for future work. iv The parts III and IV correspond to chapters 4 to 11, which are based on 8 scientific papers, 3 of which already published/accepted in scientific journals, 3 under review and 2 submitted. v Abstract Coagulation/flocculation using ferrous sulphate (FeSO 4 .7H 2 O) as coagulant was studied in this work for the removal of organic compounds and color from simulated cotton, acrylic and polyester dyeing wastewaters. The effect of the coagulant dose, temperature, pH, stirring speed and stirring time on the removal of dissolved organic carbon (DOC) and color was assessed for each effluent. Then the effect of the stirring speed, stirring time and flocculant (Magnafloc 155 or Superfloc C-573) dose on flocculation was also evaluated at the optimal conditions previously determined in the coagulation stage. The obtained results allowed concluding that the optimal operating conditions vary with the effluent and that the overall process (coagulation/flocculation) is very efficient as regards color removal (91.4% for cotton, 93.8% for acrylic effluents; polyester effluent is practically colorless). However, the DOC removal is not very significant (33.3%, 45.4% and 28.3% for polyester, cotton and acrylic dyeing effluents, respectively). On the other hand, one can take advantage of the remaining dissolved iron content for further integrating this treatment with an iron catalyzed Fenton process, thus reducing the consumption of chemicals in the overall treatment; such reduction depends on the effluent nature, but the use of this previous treatment stage facilitates the chemical oxidation in the subsequent one. A similar coagulation/flocculation treatability study was conducted using ferric sulphate (Fe 2 (SO 4 ) 3 ) as coagulant. The influence of pH and Fe 3+ concentration in both color and DOC removal from the same effluents was assessed in the coagulation stage. The effect of the type and flocculant dose was also evaluated at the better operating conditions found in the coagulation step. Once again the optimum pH and the better coagulant and flocculant doses were found to depend on the effluent under study. Maximum DOC removals of 40.2, 43.0 and 16.5% were found for polyester, cotton and acrylic dyeing wastewaters, respectively. The color removal for the acrylic dyeing effluent (44.7%) was slightly higher than for the cotton one (33.2%); both were however much smaller as compared to the use of ferrous salt. Other treatment approaches were applied to the same effluents. The Fenton's reagent was applied to the acrylic effluent previously treated by coagulation/flocculation (Approach 1) for organic matter and color removal, while improving the biodegradability. The initial iron load varied from the residual soluble iron resulting from coagulation/flocculation (275 mg Fe/L) up to 400 mg/L, by adding ferrous sulfate. The combination of the two treatments led to overall removals of 99.8, 84.2 and 78.6% for color, DOC and chemical vi oxygen demand (COD), respectively, and to a final effluent that meets the legislated discharge limits. The Fenton process was also directly applied to the same effluent (Approach 2). Under the optimal conditions, the color removal (99.5%) was similar to that obtained in the combined process, but DOC and COD removals were lower (66.5 and 65.1%, respectively). An improvement of the wastewater biodegradability was observed, both in terms of the specific oxygen uptake rate and biochemical oxygen demand:chemical oxygen demand (BOD 5 :COD) ratio. The effluent toxicity (inhibition of V. Fischeri) also decreased. The use of Fenton’s reagent followed by coagulation/flocculation (Approach 3) at the optimal conditions led to the higher color and organic matter removals for this effluent (99,7, 75,8 e 80,1% for color, COD and DOC, respectively). However, the Approach 1 permits to reach a treated effluent meeting the discharge standards at the smallest operating cost (~7 €/m 3 ). Regarding the cotton effluent, the operating cost is also higher in Approach 2 and Approach 3 due to the required dose of hydrogen peroxide. The application of the Fenton’s process before coagulation/flocculation provided an effluent that meets the discharge limits, with global organic matter removals of 55.6% for COD, 42.7% for BOD 5 and 70.4% for DOC, and almost complete color reduction (99.6%). However, the combination of coagulation/flocculation with Fenton’s oxidation (Approach 1) also exhibits high overall efficiencies (61.7%, 25.8% and 71.2% for COD, BOD 5 and DOC removal, respectively, and almost complete decolorization) with lower costs associated with chemicals consumption (0.83 €/m 3 ). The same treatment approaches were also applied to the simulated polyester dyeing effluent. The effect of Fe 2+ dose, initial H 2 O 2 concentration and temperature on organic matter by Fenton’s oxidation was evaluated in Approaches 1 and 2, while in Approach 3 only the influence of pH and flocculant dose was assessed in the coagulation/flocculation process. A slight increase in the specific oxygen uptake rate (SOUR) of the effluent was observed in Approaches 1 and 2 (from 27.0 to 28.5-30.0 mgO 2 /(g VSS h)) and the inhibition to Vibrio Fischeri was eliminated after Fenton’s oxidation. In all cases, an effluent that complies with discharge standards was obtained; however, Approach 3 leads to smaller operating costs with chemicals. The use of dissolved iron resulting from Fenton’s oxidation as coagulant in the second stage is thus an efficient and economically attractive strategy for treating this effluent. vii The simulated effluents were also subjected to the photo-Fenton process, aiming at reducing the consumption of chemicals, as compared to the dark Fenton process, while simultaneously minimizing the energy costs by using solar radiation. The reduction of the hydrogen peroxide dose is limited by the need of achieving treated effluents complying with discharge limits. The costs associated with the use of artificial radiation in the photoFenton process (17.4, 9.6 and 2.9 €/m 3 for acrylic, cotton and polyester effluents, respectively) are still too high. The use of (simulated) solar light allows obtaining high removals of color (>98-99%) and significant COD (30.1-72.0%) and DOC (46.2-71.5%) abatements at an operating cost reduced by a factor of ca. 3. Treated effluents by the solar photo-Fenton process also meet the discharge standards. As the acrylic dyeing effluent is practically non biodegradable, only the biological treatability of polyester and cotton dyeing effluents was evaluated. The biodegrabability after Fenton’s oxidation was also assessed for all effluents. Raw and chemically oxidized (pre-treated) wastewaters were fed to a Sequencing Batch Reactor (SBR) during 10 cycles (i.e., up to pseudo steady-state conditions). In the integrated chemical-biological process optimum doses of Fe(II) and H 2 O 2 (for biodegradability enhancement and maximization of color and DOC removals) were determined for Fenton’s oxidation, with the simultaneous objective of minimizing the operating costs. The integration of Fenton’s oxidation with a downstream SBR provides much better removals of organic matter (87.7 – 98.2% for COD, 83.2 – 94.5% for BOD 5 and 91.2 – 98.4% for DOC, depending on the particular textile effluent) and color (>98.5%) than the biological or chemical treatment alone. Besides, such integrated treatment allows to meet the discharge limits with a reduction of the operating costs, in the range 24-44 % comparatively to Fenton’s oxidation alone. This study also focused on the treatability evaluation of industrial dyeing wastewaters; due to time limitations only one cotton dyeing wastewater was used. Four treatment approaches, including single and integrated processes, were studied, namely: coagulation/flocculation per se and its combination with Fenton oxidation (Approach 1), Fenton’s process alone (Approach 2) and its integration with either coagulation/flocculation (Approach 3) or biological oxidation in SBR (Approach 4). Biological degradation of the raw wastewater in SBR was not tested because the ratio BOD 5 :COD and the value of SOUR are very small, which indicates low biodegradability. All the considered approaches provided a wastewater that meets the discharge limits, however Approaches 1 and 3 led to smaller operating costs (0.83 and 0.87 €/m 3 , xiv 3.2 Textile Dyeing Wastewaters ............................................................................65 3.2.1 Simulated Textile Dyeing Wastewaters ................................................................ 65 3.2.1.1 Dyes………………………..…………………………………….………………………..65 3.2.1.2 Auxiliary Chemicals….....………………………………………………………………..66 3.2.1.3 Preparation of the Simulated Textile Dyeing Effluents…….………………………..69 3.2.2 Real Cotton Dyeing Wastewater .......................................................................... 75 3.3 Analytical Methods ..........................................................................................77 3.3.1 Alkalinity ............................................................................................................... 77 3.3.2 Biodegradability .................................................................................................... 77 3.3.3 Biochemical Oxygen Demand .............................................................................. 77 3.3.4 Chemical Oxygen Demand .................................................................................. 78 3.3.5 Chlorides, Dissolved Phosphorus, Nitrates and Sulfates ..................................... 78 3.3.6 Color ..................................................................................................................... 78 3.3.7 Conductivity .......................................................................................................... 79 3.3.8 Dissolved Iron ....................................................................................................... 79 3.3.9 Dissolved Oxygen Carbon .................................................................................... 79 3.3.10 Hydrogen Peroxide ............................................................................................... 79 3.3.11 Inhibition of Vibrio Fischeri ................................................................................... 79 3.3.12 pH ......................................................................................................................... 80 3.3.13 Total Nitrogen ....................................................................................................... 80 3.3.14 Total Phosphorus ................................................................................................. 80 3.3.15 Total Suspended Solids and Volatile Suspended Solids ..................................... 80 3.3.16 HPLC Analyses .................................................................................................... 81 3.3.17 Zahn-Wellens Test ............................................................................................... 81 3.4 Experimental Procedure ..................................................................................82 3.4.1 Coagulation/Flocculation ...................................................................................... 82 3.4.2 Fenton´s Reaction ................................................................................................ 83 3.4.3 Photo-Fenton Oxidation........................................................................................ 84 3.2.1.1 Photo-Fenton with Artificial Radiation……..……..…………………………………………..85 3.2.1.1 Photo-Fenton using Simulated Solar Radiation……....……..…………….………………..87 3.4.4 Biological Oxidation in Sequencing Batch Reactor .............................................. 87 3.5 References .......................................................................................................89 Part III – Simulated Dyeing Wastewaters Treatment 4 Coagulation/Flocculation with Fe 2+ as Coagulant ................................. 95 4.1 Introduction ......................................................................................................95 4.2 Materials and Methods ....................................................................................95 4.2.1 Preparation of Simulated Textile Wastewaters .................................................... 95 4.2.2 Coagulation/Flocculation Experiments ................................................................. 95 4.2.3 Analytical Methods ............................................................................................... 96 xv 4.3 Results and Discussion ..................................................................................96 4.3.1 Effect of Stirring Speed and Time on the Coagulation Stage............................... 97 4.3.2 Effect of the Temperature on the Coagulation Stage ........................................... 97 4.3.3 Effect of the pH on the Coagulation Stage ........................................................... 98 4.3.4 Effect of the Coagulant (Fe 2+ ) Concentration ..................................................... 100 4.3.5 Influence of the Stirring Speed and Time in the Flocculation Stage .................. 102 4.3.6 Influence of the Flocculant Type and Dosage .................................................... 102 4.4 Conclusions ................................................................................................... 107 4.5 References ..................................................................................................... 107 5 Coagulation/Flocculation with Fe 3+ as Coagulant ............................... 113 5.1 Introduction .................................................................................................... 113 5.2 Materials and Methods .................................................................................. 114 5.2.1 Preparation of Simulated Textile Effluents ......................................................... 114 5.2.2 Coagulation/Flocculation Experiments ............................................................... 114 5.2.3 Analytical Methods ............................................................................................. 114 5.3 Results and Discussion ................................................................................ 115 5.3.1 Influence of pH ................................................................................................... 115 5.3.2 Influence of the Fe 3+ Concentration.................................................................... 116 5.3.3 Influence of the Flocculant Nature and Dose ..................................................... 118 5.3.4 Overall Process Efficiency .................................................................................. 123 5.4 Conclusions ................................................................................................... 126 5.5 References ..................................................................................................... 126 6 Integration of Physical-Chemical and Oxidation Processes for Acrylic Effluent Treatment ............................................................................................ 131 6.1 Introduction .................................................................................................... 131 6.2 Materials and Methods .................................................................................. 131 6.2.1 Preparation of the Simulated Textile Effluent ..................................................... 131 6.2.2 Experimental Procedure ..................................................................................... 131 6.2.3 Analytical Methods ............................................................................................. 132 6.3 Results and Discussion ................................................................................ 132 6.3.1 Combination of Coagulation/Flocculation plus Fenton´s oxidation and Fenton´s oxidation alone ....................................................................................................................... 132 6.3.1.1 Effect of the Ferrous Ion Concentration……………………….………………………………….133 6.3.1.2 Effect of the Hydrogem Peroxide Concentration …………….………………………………….135 6.3.1.3 Effect of the Temperature……….…………..………………….………………………………….137 6.3.1.4 Influence of pH …………………………………………….……………………………………….140 6.3.1.5 Optimized Treatment of Simulated Dyeing Wastewater …..………………………………….141 6.3.2 Fenton´s Reaction Followed by Coagulation/Flocculation ................................. 145 xvi 6.3.2.1 Effect of the pH ……………………………………………….....………………………………….146 6.3.2.2 Effect of Supperfloc C-573 Doses …..…………………………………………………...……….147 6.3.2.3 Overall Process Efficiency ……………………………………..………………………………….148 6.4 Conclusions ................................................................................................... 150 6.5 References ..................................................................................................... 151 7 Integration of Physical-Chemical and Oxidation Processes for Cotton Dyeing Effluent Treatment ............................................................................... 157 7.1 Introduction .................................................................................................... 157 7.2 Materials and Methods .................................................................................. 157 7.2.1 Preparation of the Simulated Textile Effluent ..................................................... 157 7.2.2 Experimental Procedure ..................................................................................... 158 7.2.3 Research Strategy .............................................................................................. 158 7.2.4 Analytical Methods ............................................................................................. 160 7.3 Results and Discussion ................................................................................ 160 7.3.1 Combination of Coagulation/Flocculation and Fenton’s Reagent (Approach 1) 160 7.3.1.1 Influence of Ferrous Ion Concentration ………….…………...………………………………….161 7.3.1.2 Effect of the Initial Hydrogen Peroxide Concentration ….....………………………………….162 7.3.1.3 Effect of the Temperature..……………………………………..………………………………….163 7.3.1.4 Optimized Treatment Performance …………………………...………………………………….165 7.3.2 Fenton Oxidation (Approach 2) .......................................................................... 166 7.3.2.1 Influence of Ferrous Ion Concentration ………….…………...………………………………….167 7.3.2.2 Effect of the Initial Hydrogen Peroxide Concentration ……………….....……….…………….168 7.3.2.3 Effect of the Temperature..……………………………………..………………………………….170 7.3.2.4 Optimized Treatment of the Simulated Cotton Dyeing Wastewater ….……………………….172 7.3.3 Fenton’s Oxidation Followed by Coagulation/Flocculation (Approach 3) ........... 173 7.3.3.1 Influence of pH …………………………….……….…………...………………………………….174 7.3.3.2 Effect of Magnafloc 155 Doses …………………………….....………………………………….175 7.3.3.3 Overall Process Efficiency ……………………………………..………………………………….176 7.3.4 Costs Evaluation ................................................................................................. 178 7.4 Conclusions ................................................................................................... 180 7.5 References ..................................................................................................... 181 8 Integration of Physical-Chemical and Oxidation Process for Polyester Dyeing Effluent Treatment ............................................................................... 185 8.1 Introduction .................................................................................................... 185 8.2 Materials and Methods .................................................................................. 185 8.2.1 Preparation of Synthetic Textile Wastewaters ................................................... 185 8.2.2 Experimental Procedure ..................................................................................... 186 8.2.3 Analytical Methods ............................................................................................. 186 8.3 Results and Discussion ................................................................................ 187 8.3.1 Combination of Coagulation/Flocculation and Fenton Reagent (Approach 1) ... 187 xvii 8.3.1.1 Influence of Ferrous Ion Concentration Added During the Chemical Oxidation Stage ……………………………………………………………….…………...………………………………….188 8.3.1.2 Effect of the Initial Hydrogen Peroxide Concentration on the Chemical Oxidation Stage……..……………………………………………..…………….....………………………………….189 8.3.1.3 Effect of the Temperature During the Chemical Oxidation Stage ….………………………….190 8.3.1.4 Optimized Integrated Coagulation/Flocculation plus Fenton's Oxidation ……..…………….191 8.3.2 Fenton’s Oxidation (Approach 2) ........................................................................ 193 8.3.2.1 Influence of Ferrous Ion Concentration ………….…………...………………………………….194 8.3.2.2 Effect of the Initial Hydrogen Peroxide Concentration ….....………………………………….195 8.3.2.3 Effect of the Temperature.….…………………………………..………………………………….197 8.3.2.4 Optimized Treatment by Fenton's Oxidation……..…………...………………………………….198 8.3.3 Fenton’s Oxidation followed by Coagulation/Flocculation (Approach 3) ............ 200 8.3.3.1 Influence of pH in the Coagulation Process….….…………...………………………………….201 8.3.3.2 Effect of Superfloc C-573 Doses ………………………….....……………….………………….202 8.3.4 Operating Costs .................................................................................................. 205 8.4 Conclusions ................................................................................................... 207 8.5 References ..................................................................................................... 208 9 Simulated Dyeing Textile Effluents Treatment by the Photo-Fenton Process ............................................................................................................. 213 9.1 Introduction .................................................................................................... 213 9.2 Materials and Methods .................................................................................. 213 9.2.1 Preparation of Simulated Textile Wastewaters .................................................. 213 9.2.2 Experimental Procedure ..................................................................................... 213 9.2.3 Analytical Methods ............................................................................................. 214 9.3 Results and Discussion ................................................................................ 214 9.3.1 Photoreactor with Artificial Radiation .................................................................. 214 9.3.1.1 Comparison Between Direct Photolysis, UV-visible+H2O2 and Photo-Fenton Processes ………………………….…………..…………………………………….………………………………….216 9.3.1.2 Photo-Fenton Process….……………….………………….………….………………………….218 9.3.1.2.1 Effect of Hydrogen Peroxide Concentration….……….…………………………………………………..218 9.3.1.2.2 Effect of Radiation Intensity …………………………………….………………………………..………….222 9.3.1.2.3 Operating Costs ………………………………………………….………….………………………………….224 9.3.2 Photoreactor with Simulated Solar Radiation ..................................................... 227 9.4 Conclusions ................................................................................................... 232 9.5 References ..................................................................................................... 233 10 Simulated Textile Dyeing Effluents Treatment by SBR alone and Combined with Fenton’s Oxidation ................................................................ 237 10.1 Introduction .................................................................................................... 237 10.2 Materials and Methods .................................................................................. 237 10.2.1 Preparation of the Simulated Textile Effluents ................................................... 237 xviii 10.2.2 Experimental Procedure ..................................................................................... 237 10.2.3 Analytical Methods ............................................................................................. 238 10.3 Results and Discussion ................................................................................ 238 10.3.1 Biological Treatment ........................................................................................... 238 10.3.2 Integration of Fenton’s Reagent Followed by Biological Treatment ................... 243 10.3.3 Costs Evaluation ................................................................................................. 251 10.4 Conclusions ................................................................................................... 252 10.5 References ..................................................................................................... 253 Part IV – Real Cotton Dyeing Wastewater 11 Cotton Dyeing Wastewater Treatment .................................................. 259 11.1 Introduction .................................................................................................... 259 11.2 Operating Costs ............................................................................................. 261 11.3 Materials and Methods .................................................................................. 262 11.3.1 Experimental Procedure ..................................................................................... 262 11.3.2 Analytical Methods ............................................................................................. 262 11.4 Results and Discussion ................................................................................ 263 11.4.1 Textile Deying Wastewater ................................................................................. 263 11.4.2 Coagulation/Flocculation plus Fenton’s Reaction (Approach 1) ........................ 263 11.4.3 Fenton’s Oxidation (Approach 2) ........................................................................ 266 11.4.4 Integration of Fenton’s Oxidation and Coagulation/ Flocculation (Approach 3) . 269 11.4.5 Combination of Fenton´s Reaction and SBR (Approach 4) ............................... 272 11.5 Conclusions ................................................................................................... 275 11.6 References ..................................................................................................... 276 Part I – Conclusions and Suggestion for Future Work 12 Concluding Remarks and Forthcoming Work ...................................... 283 12.1 Concluding Remarks ..................................................................................... 283 12.1.1 Simulated Textile Dyeing Effluents ..................................................................... 283 12.1.2 Industrial Cotton Dyeing Wastewater ................................................................. 285 12.1.3 Brief Comparison of Processes .......................................................................... 285 12.2 Forthcoming Work ......................................................................................... 287 Appendix ........................................................................................................... 291 A.1 Supporting Information for Chapter 4 ……………………...…………….………291 A.2 Supporting Information for Chapter 9 ………………………………...….………293 xix List of Figures Part I – Introduction and State of Art Figure 1.1 – Textile industry geoghaphic distribuition in Portugal …………………………………….. 7 Figure 1.2 – Representative flowchart of textile and clothing manufacturing process ……………… 9 Part II – Experimental Section Figure 3.1 – Scheme of polyester fibers dyeing: a) fiber preparation, b) dyeing and c) reduction washing…………………………………………………………………...………………………………… 72 Figure 3.2 – Scheme of acrylic fibers dyeing …………………………………………….………….… 73 Figure 3.3 – Scheme of cotton fibers dyeing: a) fiber preparation, b) dyeing and c) washing ……………………………………………………...………………………………………….………….… 73 Figure 3.4 – UV/visible spectrum for polyester, acrylic and cotton wastewaters ……..…………… 75 Figure 3.5 – UV/visible spectrum for real cotton dyeing wastewater ……...………………………… 76 Figure 3.6 – Diagram of the Jar-test set-up ……………………………….…………………………… 82 Figure 3.7 – Diagram of Fenton’s oxidation set-up ……………………….…………………………… 83 Figure 3.8 – Diagram of the photo-Fenton set-up with mercury lamp TQ 150 …………………….. 84 Figure 3.9 - Variation of the radiation intensity with the Solophenyl Green BLE 155% concentration circulating in the photo-reactor jacket …………………………………………………………………... 86 Figure 3.10 – Diagram of the sun-test set-up ………………………………………………………..… 87 Figure 3.11 – Diagram of the SBR set-up ……………………………………………………………… 88 Part III – Simulated Dyeing Wastewaters Treatment Figure 4.1 – Variation of DOC (a) and color (b) removals with temperature in the coagulation stage for the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, [Fe 2+ ]=200 mg/L and pH=8.3). ………………………………………………….………………………………………………… 98 Figure 4.2 – Influence of pH on DOC (a) and color (b) removals by coagulation applied to the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, [Fe 2+ ]=200 mg/L and T =T ambient =22-23 ºC) ........................................................................................................................ 99 Figure 4.3 – Variation of DOC (a) and color (b) removals with the concentration of coagulant (Fe 2+ ) for the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =23-25 ºC and pH polyester =8.3, pH cotton =9.4 and pH acrylic =7.2) ..................................................................................100 Figure 4.4 - Variation of DOC (a) and color (b) removals with the dose of flocculant (Magnafloc 155) for the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =23-25 ºC, pH polyester =8.3, pH cotton =9.4, pH acrylic =7.2, [Fe 2+ ] polyester =[Fe 2+ ] cotton =200 mg/L, [Fe 2+ ] acrylic =3000 mg/L, v flocculation =20 rpm and t flocculation =15 min) ........................................................................................ 101 xx Figure 4.5 - Variation of DOC (a) and color (b) removals with the dose of flocculant (Superfloc C573) for the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =23-25 ºC, pH polyester =8.3, pH cotton =9.4, pH acrylic =7.2, [Fe 2+ ] polyester =[Fe 2+ ] cotton =200 mg/L, [Fe 2+ ] acrylic =3000 mg/L, v flocculation =20 rpm and t flocculation =15 min) ........................................................................................ 104 Figure 5.1 – Influence of pH in DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, [Fe 3+ ] polyester = [Fe 3+ ] cotton = 200 mg/L, [Fe 3+ ] acrylic = 500 mg/L and T=T ambient = 22-23 ºC) .................................................................................................................... 116 Figure 5.2 – Effect of Fe 3+ concentration on DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, T=T ambient = 23-25 ºC and pH polyester = 9.4, pH cotton = 5.0 and pH acrylic = 8.3) ................................................................................................................... 117 Figure 5.3 – Effect of Magnafloc155 concentration on DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, T=T ambient = 23-26 ºC, pH polyester = 9.4, pH cotton = 5.0, pH acrylic = 8.3, [Fe 3+ ] polyester = 500 mg/L, [Fe 3+ ] cotton = 200 mg/L, [Fe 3+ ] acrylic = 1000 mg/L, v flocculation = 20 rpm and t flocculation = 15 min) ..................................................................................... 119 Figure 5.4 – Effect of Superfloc C-573 concentration on DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, T = T ambien t = 23-26 ºC, pH polyester = 9.4, pH cotton = 5.0, pH acrylic = 8.3, [Fe 3+ ] polyester = 500 mg/L, [Fe 3+ ] cotton = 200 mg/L, [Fe 3+ ] acrylic = 1000 mg/L, v flocculation = 20 rpm and t flocculation = 15 min) ..................................................................................... 120 Figure 6.1 - Variation of DOC removal and k’ with the total iron concentration, in the first (a) and c), respectively) and second experiment (b) and (d), respectively) (initial pH=3.5, T=30 °C, initial [H 2 O 2 ]=5 g/L) …………………………………………………………………………………………….. 134 Figure 6.2 - Influence of the H 2 O 2 concentration on DOC removal and k’ in the first (a) and c), respectively) and second experiment (b) and d), respectively) (initial pH=3.5, T=30 °C, initial [Fe]=350 mg/L) …………………………………………………………………………………………... 136 Figure 6.3 - Effect of temperature on DOC removal and k’ in the first (a) and c), respectively) and second experiment (b) and d), respectively) (initial pH=3.5, [Fe]=350 mg/L, [H 2 O 2 ] 1st exp=3.5 g/L, [H 2 O 2 ] 2nd exp=20 g/L) ………………………………………………………………………………….... 139 Figure 6.4 - Effect of temperature on the residual hydrogen peroxide concentration in the first (a) and second experiment (b) (initial pH=3.5, [Fe]=350 mg/L, [H 2 O 2 ] 1st exp=3.5 g/L, [H 2 O 2 ] 2nd exp=20 g/L) ………………………………………………………………………………………………………... 140 Figure 6.5 - Variation of DOC removal (a) and k’ (b) with the initial pH in the first experiment (T=50 °C, [Fe]=350 mg/L and [H 2 O 2 ]=3.5 g/L) ……………………………………………………………….. 140 Figure 6.6 - Evolution of the inhibition of Vibro fischeri of samples taken along 60 min of Fenton’s reaction for contact times of 5, 15 and 30 min in the first (a) and second experiment (b) (pH= 3.5, T=50 °C, [Fe]=350 mg/L and [H 2 O 2 ] 1st exp=3.5 g/L, [H 2 O 2 ] 2nd exp=20 g/L) ……………………..… 143 Figure 6.7 - Time evolution of HPLC chromatogram in the first (a) and second experiment (b) (pH= 3.5, T=50 °C, [Fe]=350 mg/L and [H 2 O 2 ] 1st exp=3.5 g/L, [H 2 O 2 ] 2nd exp=20 g/L) ………………….. 143 Figure 6.8 – Variation of DOC (a) and color (b) removals with pH in the coagulation stage for different doses of hydrogen peroxide applyed in the previous Fenton’s process - runs #1, #2 and #3 (v coagulation =150 rpm, t coagulation =3 min, [Fe dissolved] run #1 = 75.5 mg/L, [Fe dissolved] run #2 =118.1 mg/L, [Fe dissolved] run #3 =275 mg/L and T =T ambient = 22-24 ºC) ………………………………….… 146 Figure 6.9 – Variation of DOC (a) and color (b) removals with flocculant concentration in the flocculation step for different hydrogen peroxide doses applyed in the previous Fenton’s process - runs #1, #2 and #3 (v coagulation =150 rpm, t coagulation =3 min, [Fe dissolved] run #1 =75.5 mg/L, [Fe xxi dissolved] run #2 =118.1 mg/L, [Fe dissolved] run #3 =275 mg/L and T =T ambient = 22-24 ºC, v flocculation =20 rpm, t flocculation =15 min) …………………………………………………………………………………... 147 Figure 7.1 - Schematic diagram of process configurations adopted ………………………………. 159 Figure 7.2 – Variation of dissolved organic carbon (a) and color (b) removal along time with the iron dose during the Fenton reaction after the coagulation/flocculation stage – Approach 1 (initial pH=3.5, T=30 ºC, [H 2 O 2 ] o =500 mg/L) ………...……………………………………………………….. 161 Figure 7.3 – Variation of dissolved organic carbon (a) and color (b) removal along time with the concentration of H 2 O 2 added during the Fenton’s reaction after the coagulation/flocculation stage – Approach 1 (initial pH=3.5, T=30 ºC, [Fe]=100 mg/L) ………...………………………………………163 Figure 7.4 – Variation of dissolved organic carbon (a) and color (b) removal along time with the temperature during the Fenton reaction after the coagulation/flocculation stage – Approach 1 (initial pH=3.5, [Fe]=100 mg/L and [H 2 O 2 ] o =500 mg/L) ………………………...…………………………… 165 Figure 7.5 – Variation of dissolved organic carbon (a), color (b) removal and specific oxygen uptake rate (c) along time with the initial concentration of Fe 2+ during the Fenton reaction – Approach 2 (initial pH=3.5, T=30 ºC, [H 2 O 2 ] o =5 g/L) ………………………………………………………………..168 Figure 7.6 – Variation of dissolved organic carbon (a), color (b) removal and specific oxygen uptake rate (c) along time with the initial concentration of H 2 O 2+ during the Fenton reaction – Approach 2 (initial pH=3.5, T=30 ºC, [Fe 2+ ] o =300 mg/L) …………………………………………………………... 169 Figure 7.7 – Variation of dissolved organic carbon (a), color (b) removal and specific oxygen uptake rate (c) along time with the temperature during the Fenton reaction – Approach 2 (initial pH=3.5, [Fe 2+ ] o =300 mg/L and [H 2 O 2 ] o =10 g/L) ………………………………………………………………… 171 Figure 7.8 – Variation of DOC (a) and color (b) removals with pH during the coagulation stage – Approach 3 – for different doses of hydrogen peroxide employed in the previous Fenton’s process in runs #1, #2 and #3 (v coagulation =150 rpm, t coagulation =3 min, [Fe dissolved ] run #1 =52.1 mg/L, [Fe dissolved ] run #2 =85.6 mg/L, [Fe dissolved ] run #3 =167 mg/L and T =T ambient =23-25 ºC) ……………………………….. 173 Figure 7.9 – Variation of DOC (a) and color (b) removals with the flocculant concentration during the flocculation step – Approach 3 – for the different doses of hydrogen peroxide employed in the previous Fenton’s process in runs #1, #2 and #3 (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =2325 ºC, pH=5.0, [Fe dissolved ] run #1 =52.1 mg/L, [Fe dissolved ] run #2 =85.6 mg/L, [Fe dissolved ] run #3 =167 mg/L, v flocculation =20 rpm and t flocculation =15 min) ……………………………………………………………….. 175 Figure 7.10 – Effect of Fe and H 2 O 2 doses in the total operating cost of wastewater treatment by coagulation/flocculation plus Fenton processes – Approach 1 (a), Fenton’s reagent – Approach 2 (b) and influence of Magnafloc 155 and H 2 O 2 concentration in the total treatment costs by Fenton’s process followed by coagulation/flocculation – Approach 3 (c) …………………………………….. 179 Figure 8.1 – Variation of DOC removal (a) and percentage of H 2 O 2 consumption (b) along time, with the iron dose added during the 2 nd stage – Fenton oxidation in Approach 1 (initial pH=3.5, T=30 ºC, initial [H 2 O 2 ]= 500 mg/L) …………………………………………………………………….. 188 Figure 8.2 – Effect of H 2 O 2 dose in DOC removal (a) and percentage of H 2 O 2 consumption (b) along time during the 2 nd stage i.e. Fenton oxidation in Approach 1 (initial pH=3.5, T=30 ºC, [Fe]=200 mg/L) …………………………………………………………………..………………………. 190 Figure 8.3 – Variation of DOC removal (a) and percentage of H 2 O 2 consumption (b) along time with the reaction temperature during the 2 nd stage – Fenton oxidation in Approach 1 (initial pH=3.5, [Fe]=200 mg/L and initial [H 2 O 2 ]=1000 mg/L) …………………………….………………………….. 191 xxii Figure 8.4 – Evolution of the inhibition of V. fischeri at 5, 15 and 30 minutes of contact (a) and HPLC chromatograms (b) of samples taken along time during the 2 nd stage – Fenton oxidation in Approach 1 (initial pH=3.5, T=50 ºC, initial [Fe]=200 mg/L and initial [H 2 O 2 ]=1000 mg/L) ……………………………………………………………………………………………………………... 192 Figure 8.5 – Variation of DOC removal (a), percentage of H 2 O 2 consumption (b) and k’(c) along time with the initial Fe 2+ dose during Fenton’s reaction in Approach 2 (initial pH=3.5, T=30 ºC, initial [H 2 O 2 ]= 5.0 g/L) ………………………………………………………………………………………….. 193 Figure 8.6 – Variation of DOC removal (a), percentage of H 2 O 2 consumption (b) and k’(c) along time with the initial H 2 O 2 dose during Fenton’s reaction in Approach 2 (initial pH=3.5, T=30 ºC, initial [Fe 2+ ]=350 mg/L) ………………………………………………………………………………….. 196 Figure 8.7 – Variation of DOC removal (a), percentage of H 2 O 2 consumption (b) and k’(c) along time with the reaction temperature during Fenton’s reaction in Approach 2 (initial pH=3.5, initial [Fe 2+ ]=350 mg/L and initial [H 2 O 2 ]=2.5 g/L) …………………………………………………………... 198 Figure 8.8 – Evolution of V. fischeri inhibition after 5, 15 and 30 minutes of contact (a) and HPLC chromatograms (b) of samples taken along time during Fenton’s oxidation in Approach 2 (initial pH=3.5, T=50 ºC, initial [Fe 2+ ]=350 mg/L and initial [H 2 O 2 ]=2.5 g/L) ………………………………. 199 Figure 8.9 – Variation of DOC removal with pH during the coagulation stage – Approach 3 – for the different doses of hydrogen peroxide employed in the previous Fenton’s process in runs #1, #2 and #3 (v coagulation =150 rpm, t coagulation =3 min, [Fe] dissolved run #1 = 64.8mg/L, [Fe] dissolved run #2 =88.5 mg/L, [Fe] dissolved run #3 =222 mg/L and T =T ambient =22-24 ºC) ……………………………………………..… 201 Figure 8.10 – Variation of DOC removal with the flocculant concentration during the flocculation step – Approach 3 – for the different doses of hydrogen peroxide employed in runs #1, #2 and #3 of the previous Fenton’s process (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =22-24 ºC, pH=5.0, [Fe] dissolved run #1 = 64.8mg/L, [Fe] dissolved run #2 =88.5 mg/L, [Fe] dissolved run #3 =222 mg/L, v flocculation =20 rpm and t flocculation =15 min) ………………………………………………………………………………. 203 Figure 8.11 – Effect of Fe and H 2 O 2 doses on the operating cost of wastewater treatment by: coagulation/flocculation plus Fenton processes – Approach 1 (a) or Fenton’s reagent – Approach 2 (b), and influence of [Superfloc C-573] and [H 2 O 2 ] on the operating cost of Fenton’s process followed by coagulation/flocculation – Approach 3 (c) ………………………………………………. 206 Figure 9.1 – Evolution of DOC and color removal for acrylic (a), cotton (b) and polyester (c) wastewater during 120 minutes of direct photolysis, H 2 O 2 -assisted photolysis ([H 2 O 2 ] acrylic =20 g/L, [H 2 O 2 ] cotton =10 g/L and [H 2 O 2 ] polyester =2.5 g/L) or photo-Fenton ([H 2 O 2 ] acrylic =20 g/L, [H 2 O 2 ] cotton =10 g/L and [H 2 O 2 ] polyester =2.5 g/L, [Fe 2+ ] cotton =300 mg/L, [Fe 2+ ] acrylic =[Fe 2+ ] polyester =350 mg/L). In all cases radiation intensity = 500 W/m 2 , pH=3.5, T=50ºC …………………………………………………….. 216 Figure 9.2 – Effect of H 2 O 2 dose on DOC and color removal in the photo-Fenton process for acrylic (a), cotton (b) and polyester (c) wastewaters (radiation intensity = 500 W/m 2 , T=50 ºC, pH=3.5, Fe 2+ :H 2 O 2 acrylic =1:57, Fe 2+ :H 2 O 2 cotton =1:33, Fe 2+ :H 2 O 2 polyester =1:7 – wt. ratios) ………………… 219 Figure 9.3 – Effect of radiation intensity on DOC and color removal of the acrylic effluent during the photo-Fenton process for different dosages of hydrogen peroxide: 6.5 g/L (a), 10.0 g/L (b) or 20.0 g/L (c) (T=50 ºC, Fe 2+ :H 2 O 2 =1:57 and pH=3.5) ……………………………………………………… 223 Figure 9.4 – Effect of hydrogen peroxide doses and radiation intensity on the total operating cost associated with the photo-Fenton process with TQ 150 lamp for treating acrylic (a), cotton (b) and polyester (c) wastewaters ………………………………………………………………………………. 226 xxiii Figure 9.5 – Effect of H 2 O 2 dose on DOC and color removal with simulated solar radiation at intensity of 253 W/m 2 for acrylic (a), cotton (b) and polyester (c) wastewaters (T=50 ºC, Fe 2+ :H 2 O 2 acrylic =1:57, Fe 2+ :H 2 O 2 cotton =1:33 Fe 2+ :H 2 O 2 polyester =1:7, pH=3.5) ……………………………….… 228 Figure 9.6 – Effect of H 2 O 2 and Fe 2+ doses on the total operating cost associated with the photoFenton with simulated solar radiation for treating acrylic (a), cotton (b) and polyester (c) wastewaters ……………………………………………………………………………………………… 231 Figure 10.1 – Evolution of percentage of COD degradation along time in Zahn-Wellens test for acrylic wastewater ………………………………………………………………………………………. 233 Figure 10.2 - Variation of COD (a), BOD 5 (b), DOC (c), total nitrogen (d) and color (e) removals along 10 cycles of SBR operation for polyester and cotton wastewaters ……………………….… 240 Figure 10.3 - Variation of COD (a), BOD 5 (b), DOC (c), total nitrogen (d) and color (e) removals during 10 cycles of SBR operation for acrylic effluent, previously treated by Fenton’s oxidation. Runs#1 to #3 represent experiments with decreasing doses of chemicals in the Fenton’s stage ...……………………………………………………………………………...……………………………. 248 Figure 10.4 - Variation of COD (a), BOD 5 (b), DOC (c), total nitrogen (d) and color (e) removals during 10 cycles of SBR operation for synthetic cotton dyeing effluent, previously treated by Fenton’s reaction. Runs#1 to #3 represent experiments with decreasing doses of chemicals in the Fenton’s stage …………………………………………………………………………………………… 249 Figure 10.5 - Evolution of COD (a), BOD 5 (b), DOC (c) and total nitrogen (d) removals during 10 cycles of SBR operation for polyester dyeing wastewater, previously treated by Fenton’s reaction. Runs#1 to #3 represent experiments with decreasing doses of chemicals in the Fenton’s stage ....................................................................................................................................................... 250 Figure 10.6 - Total operating costs for biological, Fenton alone and integrated treatment of acrylic, cotton and polyester dyeing wastewaters …………………………………………………………….. 252 Part IV – Real Cotton Dyeing Wastewater Figure 11.1 - Schematic diagram of all process configurations adopted ………………………….. 260 Figure 11.2 - Effect of H 2 O 2 concentration on COD, BOD 5 , DOC and color removals during Fenton’s oxidation (Approach 2) (initial pH=3.5, T=50 ºC, t = 60 min and [Fe 2+ ] = 300 mg/L) ….. 266 Figure 11.3 - Effect of Fe 2+ concentration on COD, BOD 5 , DOC and color removals during Fenton’s oxidation (Approach 2) (initial pH=3.5, T=50 ºC, t = 60 min and [H 2 O 2 ] = 1.25 g/L) ……………… 268 Figure 11.4 - Variation of COD (a), DOC (b), BOD 5 (c), color (d) total nitrogen (e) and total phosphorus (f) removals along 10 cycles of SBR operation, after treatment by Fenton’s oxidation. Runs #3 to #1 refer to Fenton’s stage with progressively decreasing doses of chemicals ……… 273 Figure 11.5 - Operating costs of Fenton alone and Fenton plus SBR for treatment of a real cotton dyeing wastewater ………………………………………………………………………………………. 275 Appendix Figure A.1 – Influence of the stirring rate on the coagulation stage for DOC (a) and color (b) removal from polyester and cotton simulated effluents (t coagulation =3 min, T=T ambient =23-25 ºC, [Fe 2+ ]=200 mg/L and pH=8.3) ....................................................................................................... 291 KTN Kjeldhal Total Nitrogen [mg/L] P Power [W] SRT Sludge Retention Time [day] SOUR or k’ Specific Oxygen Uptake Rate [mg O 2 /(g VSS .h)] V coagulation Stirring Speed in Coagulation Step [rpm] V flocculation Stirring Speed in Flocculation Step [rpm] T Temperature [ºC] T amb Ambient Temperature [ºC] T Time [min] t feed Time of Feeding [days] t coagulation Time of Coagulation Stage [min] t flocculation Time of Flocculation Stage [min] t reaction Time of reaction [min] TDS Total Dissolved Solids [mg/L] TOC Total Organic Carbon [mg C/L] TS Total Solids [mg/L] TSS Total Suspensed Solids [mg/L] G Velocity gradient [s -1 ] VSS Volatil Suspensed Solids [mg/L] [mg MLSS/L] Greek Letters Symbol Designation Unity λ Wavelength [nm] λ max Wavelength for Maximum Absorbance Value [nm] xxxi Abbreviations Abbreviation Designation AA – SBR Aerobic - Anaerobic Sequential Batch Reactor AOP Advanced Oxidation Process E.L.V. Emission Limit Value FCS Ferric Chloride Sludge GAC Granular Activated Carbon HPLC High Performance Liquid Chromatography R Organic compound M.A.V. Maximum Allowable Value MLSS Mixed Liquor Suspensed Solids PDMDAAC Polidimetildialilamonium Chloride PAC Polyaluminum Chloride PFC Polyferric Chloride PAS Polyalumimium Sulfate SBR Sequential Batch Reactor UV Ultra-violet hν Radiation V. fischeri Vibrio fischeri WWTP Wastewater Treatment Plant Part I Introduction and State of Art Chapter 1 Thesis Framework Part I 5 1 Thesis Framework 1.1 Introduction This chapter presents the outline and motivation of the thesis, a brief overview of the textile industry in Portugal, a short description of the industrial process, the characterization of the textile wastewaters generated and the identification of the major environmental impacts associated with the discharge of textile effluents. 1.2 Outline and Motivation Environmental protection and correction of environmental dysfunctions are key issues for effectively improving the quality of life and sustainable development. The water is used for very diverse purposes, which include domestic and public supply, irrigation, transport, industrial processes, recreation and other human activities. These activities generate heavily contaminated wastewaters, that if discharged without any treatment can cause strong negative impacts on the receiving bodies. The textile industry is known as one of the most polluting industrial sectors [Vandevivere et al., 1998], given the large amounts of wastewater rejected, the composition of the effluents and the fact that dyes are the most notorious pollutants, and often toxic [Figueiredo, 2002]. The adoption of legislation that addresses the need to control the contamination by reducing the pollutants discharged (2000/60/EC Directive) and the imposition of emission limit values (E.L.V.) by Decree - Law No. 236/98 of 1 August and maximum allowable values (M.A.V.) for the discharge of textile effluents (Ordinance No. 423/97 of 25 June) makes the study of new treatment processes a need increasingly urgent. Moreover, the possibility of reusing the treated effluent in industrial processes must necessarily be exploited, since it allows the minimization of water consumption as well as the elimination of pollutants discharge [Silva, 2003]. For the treatment of textile effluents, chemical, biological or a combination of both processes are generally envisaged. The biological treatment by activated sludge is efficient in removing the biodegradable organic matter, but often ineffective in removing Chapter 1 - Framework 6 the color from wastewaters, since this is only removed by flocculation and adsorption of the dyes to flocs of microorganisms [Halliday and Beszedits, 1986]. Chemical coagulation/flocculation is also not fully effective in removing certain dyes [Rodrigues, 2007]. As a contribution to overcome this problem it was decided to study the combination of coagulation/flocculation, chemical oxidation by Fenton’s reagent – both in darkness and under artificial or solar (simulated) radiation (photo-Fenton oxidation) – and an aerobic biological process (SBR - sequential batch reactor) to improve decolorization and organic matter removal. Research was focused on three simulated effluents (resulting from the dyeing of acrylic, cotton and polyester fibers) and the treatability of each effluent was assessed by the individual processes mentioned above and their integration in order to obtain a treated effluent complying with the discharge limits imposed by Ordinance No. 423/97 of 25 June at the lowest operation cost. Taking into account the results obtained when treating a simulated cotton dyeing wastewater, a combination of coagulation/flocculation and Fenton’s oxidation, Fenton’s oxidation alone and an integrated process consisting in Fenton’s oxidation plus coagulation/flocculation or biological oxidation in SBR, were applied to a real cotton dyeing wastewater having also in mind the need to meet the discharge limits at the lowest operating costs. 1.3 The Textile Industry 1.3.1 Economic Perspective and Textile Industry Distribution in Portugal The European textile and clothing industry, which represents approximately 7% of employment and 4% of total manufacturing output in the E.U. [Commission of the European Communities, 2003], is in a difficult economic situation due to the high competition from Asian countries like China, India and Pakistan and the abolition of import quotas by January 1 st 2005. In fact, there was a decline in the production (8.7%) and in the employment (8.4%) in 2001 and 2002 [Commission of the European Communities, 2003]. In 2003 the decrease was 4.4% and 7.1% for production and employment, respectively [Commission of the European Communities, 2004]. Part I 7 In Portugal, the textile and clothing industry has a large representation in the industrial structure with a prominent role in terms of employment and weight in the national economy [Vasconcelos, 2006]. According to the Textile and Clothing Association [ATP, 2013], in 2011 there were, in Portugal, about 7000 companies laboring in all textile and clothing sub-sectors, which accounted for 10% of Portuguese exports, 19% of employment in manufacturing industry, 8% of turnover and 8% of production. National strengths lie in geographical and cultural proximity to the European market, tradition and accumulated "know-how", moderate wage costs as regards the European levels, growing international recognition of the products, progressive development of a culture of quality and rapid response [Vasconcelos, 2006]. The textile sector in Portugal also felt pressure from the Asian market and the abolition of import quotas led to a considerable decrease of total exports since 2007 [ATP, 2013]. The textile industries in Portugal are located mainly in three regions: North, Centre and Tagus Valley, and there has been in recent years an increase in the relative weight of the North and Centre, to the detriment of Lisbon, as can be seen in Figure 1.1 [Vasconcelos, 2006]. Figure 1.1 – Textil industry geografic distribuition in Portugal (adapted from Vasconcelos, 2006). In Portugal, there are two major concentrations of the textile industry. The first one, concerning the subsectors of cotton and synthetic fibers, is found in the northern region, 0 1000 2000 3000 4000 Norte Centro Lisboa e Vale do Tejo Alentejo Algarve Açores Madeira Nº Empresas 1999 2000 2001 2002 2003 Number of Industries North Centre Lisbon Alentejo Algarve Açores Madeira Chapter 1 - Introduction 14 The uncontrolled discharge without any prior treatment of such heavily contaminated effluents (cf. Table 1.4) generates negative impacts on the environment, namely:  pH increase of the receiving waters, causing damage to fauna and flora;  Presence of high levels of dissolved solids can generate increased salinity and turbidity associated with the proliferation of microorganisms or eutrophization of the water resources;  Possible occurrence of low dissolved oxygen concentration in water due to its consumption by aerobic microorganisms that oxidize the biodegradable organic matter present in the effluent, then causing the death of aquatic organisms; the organic matter may also be degraded anaerobically, yielding toxic and unpleasant odorous compounds (such as hydrogen sulfide);  One of the most important adverse effects resulting from the discharge of textile wastewater comes from non-fixed dyes to the fiber. Because dyes present a great chemical and photolytic stability [Silva, 2003] and are visible at low concentrations (1 mg/L) [O'Neill et al., 1999], they prevent the use of water for certain uses, particularly for producing drinking water and for recreational purposes [Rodrigues, 2007 and Santos, 2009]; moreover, when ingested they pose risks associated with chronic biotransformations, as specific enzymes can produce carcinogenic and mutanogenic compounds (aromatic amines such as, toluidines, active radicals, etc.), which may cause dermatitis when in contact with the skin [Silva, 2003].  Another negative impact of dyes is associated with a decrease in sunlight penetration, affecting photosynthesis and plant growth [Rodrigues, 2007; Santos, 2009], and with disturbances in the solubility of gases causing damage to the aquatic fauna [Silva, 2003]. The competent authorities have been developping legislation that limits the concentration of these pollutants in effluents discharged, to minimize environmental impacts. For the textile sector, excluding the wool subsector, the Portuguese Legislation (Ordinace No. 423/97 of 25 June) imposes maximum allowable values (M.A.V.) for pH, COD, BOD 5 and visibile color after dilution 1:40 (Table 1.5). Part I 15 Table 1.5 – Maximum allowable values for the textile sector, excluding the wool subsector. Parameter Maximum Allowable Values pH 5.5 – 9.0 BOD 5 100 mgO 2 /L COD 250 mgO 2 /L Color not visible after diluition 1:40 The values of pH, COD, BOD 5 and color typically do not comply with the values established by law, so it is necessary to treat the textile effluents before dischage. Various studies concerning the treatment of these effluents, namely, by physical processes (coagulation/flocculation, adsorption and membrane separation), advanced chemical oxidation, biological oxidation and chemical reduction, are reported in the literature [Lourenço et al., 2001; Figueiredo, 2002; Walker et al., 2002; Malik et al., 2003; Fersi et al., 2005; Ramirez et al., 2005; Joo et al., 2007; Rodrigues, 2007]. In this thesis, coagulation/flocculation, Fenton and photo-Fenton oxidation, and biological processes were selected to treat textile dyeing wastewaters. The next chapter presents a description of these technologies and the reasons for their choice. 1.4 References Abrahart, E.N. (1977). Dyes and Their Intermediates. 2 nd Edition, Edward Arnold Ltd, London. Al-Kadasi, A.; Idris, A.; Saed, K.; Guan, C.T. (2004). Treatment of textile wastewater by advanced oxidation process – a review. International Journal, 6 (3), 222-230. AMAVE – Associação de Municípios do Vale do AVE, S.I.D.V.A. – Sistema Integrado de Despoluição do Vale do Ave (2002). Andrade, F. (2003). Remoção de cor de efluentes têxteis com tratamento de lodos ativados e um polielectrólito orgânico. Dissertação de Mestrado em Engenharia Ambiental, Departamento de Engenharia Sanitária, Universidade Federal de Santa Catarina, Florianópolis. (acess: http://www.tede.ufsc.br/teses/PGEA0163.pdf). Araújo, M. e Castro, E. M. (1984). Manual de Engenharia Têxtil, volume II. Lisboa: Fundação Calouste Gulbenkian. ATP (2013). Associação Têxtil e Vestuário de Portugal. http://www.atp.pt/gca/index.php?id=18. (last acess 23/03/2013). Chapter 1 - Introduction 16 Bisschops, I.; Spanjers, H. (2003). Literature Review on Textile Wastewater Characterisation. Environmental Technology, 24, 1399-1411. Commission of the European Communities (2003). O futuro do sector dos têxteis e do Vestuário na União Europeia alargada. Communication from the Council Commission, the European Parliament, the European Economic and Social Committee and the Committee of the Regions, Brussels. Commission of the European Communities (2004). O sector dos têxteis e do Vestuário após 2005 – Recomendações do Grupo de Alto Nível para os Têxteis e o Vestuário. Communication from the Council Commission, the European Parliament, the European Economic and Social Committee and the Committee of the Regions, Brussels. 2000/60/CE Directive of European Parliament Council, 23 October 2000, establishing a framework for Community action in the field of water policy. Easton, J. R. (1995). The dye maker's view. In Colour in Dyehouse Effluent, P. Cooper (Ed.). Oxford, The Society of dyers and Colourists, The Alden Press, 9-21. Faria, P.C.C. (2008). Catalytic Ozonation of Effluents from the Textile Industry. PhD thesis, University of Porto – Faculty of Engineering. Fersi, C.; Gzara, L;. Dhahbi, M. (2005). Treatment of textile effluents by membrane technologies. Desalination, 185 (1-3), 399-409. Figueiredo, J.M.; Rodrigues, F.; Correia, A.; Barros, M. (2000). Guia Técnico do Sector Têxtil. Lisbon. Figueiredo, S. A. R. C. (2002). Remoção de corantes têxteis em solução aquosa usando materiais naturais contendo quitina. PhD thesis, University of Porto – Faculty of Engineering. Gao, B.-Y.; Wang, Y.; Yue, Q.-Y.; Wei, J.-C.; Li, Q. (2007). Color removal from simulated dye water and actual textile wastewater using a composite coagulant prepared by ployferric chloride and polydimethyldiallylammonium chloride. Separation and Purification Technology, 54, 157-163. Halliday, P.J.; Beszedits, S. (1986). Color Removal from Textile Mill Wastewater. Canadian Textile Journal, April, 78-84. Hi, S.H.; Peng, C.F. (1994). Treatment of textile wastewater by electrochemical method, Water Research 28 (2), 277–282. Joo, D.J.; Shin, W.S.; Choi,J.-H.; Choi, S. J.; Kim, M.-C.; Han, M.H.; Ha, T. W.; Kim, Y.-H. (2007). Decolourization of reactive dyes using inorganic coagulants and synthetic polymer. Dyes and Pigments, 73, 59-64. Kim, T.-H.; Park,C.; Yang,J.;Kim, S. (2004) Comparison of disperse and reactive dye removals by chemical coagulation and Fenton oxidation. Journal of Hazardous Materials, B 112, 95-103. Lourenço, N.D.; Novais, J.M.; Pinheiro, H.M. (2001). Effect of some operational parameters on textile dye biodegradation in a sequential batch reactor. Journal of Biotechnology, 89, 163-174. Malik, P.K.; Saha, S.K. (2003). Oxidation of direct dyes with hydrogen peroxide using ferrous ion catalyst. Separation and Purification Technology, 31, 241-250. Part I 17 Mokhtari, J., Phillips, D. A. S., Taylor, J. A. (2005). Synthesis and evaluation of a series of trisazo heterobi-functional reactive dyes for cotton. Dyes and Pigments, 64 (2), 163-170. Morais, L.C.P. (1996). Tratamento de Efluentes Têxteis Simulados Usando Técnicas de Adsorção. 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Chapter 2 State of the Art Part I 21 2 State of the Art 2.1 Introduction In the present chapter the processes of coagulation/flocculation, Fenton and photoFenton’s oxidation and biological degradation in sequencing batch reactor (SBR) are reviewed, particularly their application to textile wastewater treatment. The selection of these treatment processes took into account the ease of operation, the ability to eliminate pollutants and the operating cost. 2.2 Coagulation/Flocculation Natural waters and wastewaters contain suspended or colloidal insoluble particles. Colloids are particles with diameter in the range of 0.1-1 nm [Eckenfelder, 2000], usually negatively charged. The surface attracts oppositely charged ions in solution, thereby forming a fixed Stern layer. The remaining ions present in solution form a diffuse layer around the Stern layer. The combination of the two layers is called a double layer [Eckenfelder, 2000]. The colloids are stable owing to repulsive electrostatic forces which prevent their agglomeration or flocculation [Eckenfelder, 2000]. Accordingly, these particles present a very low settling rate and thus cannot be removed by traditional gravitic processes [Eckenfelder, 2000; Samyer et al., 1994]. Colloids also exhibit attractive forces, with smaller amplitude than the repulsive ones (Van der Waals forces), with the ability to aggregate particles that surround themselves enough. For the occurrence of such particles removal it is necessary to agglomerate them, forming larger particles. Thus, the coagulation/flocculation process is based on the destabilization of colloids and subsequent formation of flocs (that occurs after addition of a polyelectrolyte or an inorganic coagulant - normally aluminium or iron salts) and makes use of a polymer to promote the flocs aggregation, which are further separated by sedimentation [Cãnizares et al., 2009]. Chapter 2 – State of the Art 22 The coagulation stage is a somewhat complicated process involving a series of physicalchemical interactions: electrostatic attraction, sorption, bridging (related to high molecular weight polymers) and inclusion in metal precipitates [Peavy et al., 1985; Sawyer et al., 1994; Eckenfelder, 2000; Alves, 2007]. Normally the destabilization of the colloids in water and wastewater treatment processes is achieved through mechanisms of charge neutralization and inclusion in metal precipitates. These mechanisms are affected by various parameters such as: type of coagulant, coagulant dose, pH, stirring rate and contact time [Metcalf & Eddy, 2003; Alves, 2007]. To determine the optimum values of the parameters for coagulation it is necessary to perform laboratory experiments, since they depend on the characteristics of the effluent to be treated and the type of coagulant used. However, in the literature can be found typical values for stirring speed around 100 rpm [Satterfield, 2004; Bose, 2010; Poland and Pagano, 2010] and stirring time in the order of 1-3 minutes [Peavy,198; Eckenfelder, 2000; Bose, 2010; Poland and Pagano, 2010]. For the treatment of textile effluents, doses of 250-1000 mg/L and pH values from 3 to 11 for Fe 2 (SO 4 ) and doses of 250-750 mg/L and pH values of 5 to 10 for Al 2 (SO 4 ) 3 .18H 2 O have been reported [Eckenfelder, 2000]. After stabilization of colloids the aggregation of particles must be promoted to obtain particles with higher diameter, which facilitates their sedimentation (flocculation step). This is achieved through collisions between particles and can be triggered by two mechanisms, perikinetic or orthokinetic flocculation [Vigneswaran and Visvanathan, 1995; Alves, 2007]. In the flocculation step it is necessary to take into account the type and dose of flocculant, stirring speed and contact time. The optimal values of these variables are also determined by performing laboratory tests and mainly varying the type and dose of flocculant, since they depend on the characteristics of the wastewater, as in the coagulation step [Alves, 2007]. Values of 10 to 45 minutes for the contact time [Peavy et al., 1985; Alves, 2007; Bose, 2010; Poland and Pagano, 2010] and 25 to 35 rpm [Phipps & Bird, 1995; Lafleur, 1997; Eckenfelder, 2000; Bose, 2010; Poland and Pagano, 2010] for the stirring speed, have been reported. The main advantages of this treatment process are the following ones: low residence/contact time, flexibility and efficiency for most classes of dyes, low capital costs, use of relatively simple equipment and simultaneous removal of other pollutants (for example allows the COD reduction). However, this technique has some disadvantages, such as: use of flocculants to increase the efficiency of the process, considerable volume Part I 23 of chemical sludge produced, necessity of adding chemicals, relatively high operating costs, and some cationic organic polymers can be toxic to fishes, even at low concentrations [Easton, 1995]. In the literature are reported studies where coagulation/flocculation or a combination of this technique with other process has been applied in the treatment of textile effluents. In the two next sections a brief description of these studies is presented. 2.2.1 Textile Wastewater Treatment by Coagulation/Flocculation In the last years various works have been reported in the open literature regarding the treatment of dye solutions and simulated or real textile wastewaters by coagulation/flocculation. Table 2.1 summarizes some of those works. Table 2.1 – Research works on the application of coagulation/flocculation for treating dye solutions and textile effluents. Dye solution or Effluent type Optimal Operating Conditions Efficiencies (%) Reference Blue Suncron RD-400 dye V coagulation = 250 rpm t coagulation = 2 min V flocculation = 40 rpm t flocculation = 15 min t sedimentation = 30 min pH = 6 [FeCl 3 .6H 2 O] = 0.93 mM COD = 84 Dye = 98 Kim et al. [2004] Yellow Suncron 3GE200 dye V coagulation = 250 rpm t coagulation = 2 min V flocculation = 40 rpm t flocculation = 15 min t sedimentation = 30 min pH = 5 [FeCl 3 .6H 2 O] = 0.74 mM COD = 88 Dye = 100 Kim et al. [2004] Blue Suncron P-3R dye V coagulation = 250 rpm t coagulation = 2 min V flocculation = 40 rpm t flocculation = 15 min t sedimentation = 30 min pH = 7 [FeCl 3 .6H 2 O] = 2.78 mM COD = 25 Dye = 61 Kim et al. [2004] Chapter 2 – State of the Art 30 HO • + H 2 O 2 → H 2 O + HO 2• (2.3) HO • + Fe 2+ →Fe 3+ + HO - (2.4) Fe 3+ + H 2 O 2 → Fe 2+ + HO 2• + H + (2.5) The Fenton process efficiency is influenced by several variables, including pH, temperature, concentration of ferrous ion and hydrogen peroxide. The pH is a crucial parameter in the Fenton process. The decrease in reaction efficiency at pH above 4 is associated with the formation of complexes of Fe 2+ [Benitez et al., 2001], precipitation of Fe(OH) 3 , which inhibits the regeneration of Fe 2+ (Equation 2.5), and also with the decomposition of hydrogen peroxide in water and oxygen [Szpyrkowicz et al., 2001]. At pH below 2, the generation of hydroxyl radicals decreases, and is almost totally suppressed at pH 1. For so low pH values the hydrogen peroxide forms H 3 O 2+ , reducing the reactivity with Fe 2+ [Schirman and Delavarenne, 1979, cited in Morais, 2005]. On the other hand, the concentration of Fe 3+ , responsible for the continued oxidation (Equation 2.5) is small [Pignatello, 1992] as the ferric iron is in the form of Fe(OH) 2+ and Fe(OH) 2+ . Various authors indicated optimal values for this parameter in the range 2-5 [Sims, 1983; Rivas et al., 2001; Zhu et al., 2001], or more specifically pH around 3 [Neyens and Baeyens, 2003], regardless the characteristics of the effluent to treat [Morais, 2005]. The reaction rate increases with increasing temperature, since it increases the kinetic constants according to the Arrhenius law, and particularly between 5 and 30-40 °C [Flaherty and Huang, 1992]. However, the extent of reaction decreases for temperatures above 40-50 °C because occurs the thermal decomposition of hydrogen peroxide into water and oxygen. In the literature there are several works reporting optimal operating temperatures between 20 and 50 °C [Gulkaya et al., 2006; Tekin et al., 2006; Sun et al., 2007]. The Fenton´s reaction also depends on the ferrous ion dose, the minimum required for the reaction to proceed at reasonable rate being between around 3 to 15 mg/L [Morais, 2005]. However, the substrate removal increases with the catalyst concentration up to a point beyond which the reaction of excess of ferrous ion with the hydroxyl radical occurs (Equation 2.4) [Walling, 1975] – the so-called scavenging effect. The required catalyst dose depends on the type of effluent to be treated; however Morais [2005] indicates values of 1:10 to 1:50 for the Fe 2+ :substrate ratio (w:w). Part I 31 Finally, the efficiency of Fenton’s oxidation increases with the hydrogen peroxide concentration but when this reagent is in excess, it reacts with the radicals (Equation 2.3 [Waling, 1975]). The required dose of H 2 O 2 to be used depends on the amount of organic compounds, but it is necessary to add an excess over the stoichiometric amount to compensate the quantity of hydrogen peroxide which decomposes into water and oxygen and also the one consumed in parallel / undesired reactions [Southworth and Voelker, 2003]. This homogeneous process has several advantages such as high efficiency, simple applicability, operation at room temperature and atmospheric pressure, and nonselectivity, i.e. ability to oxidize various pollutants at the same time. However, the main disadvantage is the generation of ferric iron sludge which requires separation and disposal and/or reuse [Hsueh et al., 2005]. 2.3.1 Textile Wastewater Treatment by Homogeneous Fenton’s Oxidation The Fenton process has been widely applied in the treatment of textile effluents. Recent studies are summarized below. Malik and Saha [2003] studied the degradation of two direct dyes (Blue 2B – B54 and Red 12B - R31) by the Fenton process. A parametric study was performed to evaluate the effect of various parameters. The maximum dye removal (97%) was achieved for pH=3, [H 2 O 2 ]=1.47 and 2.94 mM for B54 and R31, respectively, [Fe 2+ ]=8.93x10 -2 mM, T=40 ºC and t=30 minutes. The authors also assessed the effect of the presence of chlorides and sulfates in the removal efficiency and found that up to 600 mg/L the sulfate ion had no effect on the removal of the two dyes, but the chloride ion negatively affected the dyes removal, because this anion “scavenges” the hydroxyl radical. Other authors [Swaminathan et al., 2003] evaluated the effect of process variables on the decolorization and degradation of two commercial azo dyes (Red M5B and Blue MR) and H-acid dye, by the Fenton’s reaction. For the Red M5B dye the maximum color (~100%) and DOC (78%) removals were achieved by using 10 mg/L of Fe 2+ , 400 mg/L of H 2 O 2 , pH=3 and 120 minutes of reaction time. For the Blue MR dye high color and COD removals were obtained (99% for COD and ~100% for color) in the following conditions: Chapter 2 – State of the Art 32 20 mg/L, 500 mg/L, 3 and 20 minutes for Fe 2+ dose, H 2 O 2 concentration, pH and reaction time, respectively. Finally 99% of COD and ~100% of color removals were achieved for the H-acid dye by using 25 mg Fe 2+ /L, 500 mg H 2 O 2 /L, pH=3 and t=120 minutes. Decolorization followed 1 st order kinetics and the computed rate constant was greater for H-acid dye (k = 0.0106 min -1 ) followed by red M5B dye (k = 0.0413 min -1 ) and finally blue MR (k = 0.0727 min -1 ). The sulfate concentration in H-acid and Blue MR solutions and the concentration of chlorides and sulfates in Red M5B solutions increased with reaction time allowing the authors to conclude that these anions are replaced in the structure of the dyes when the HO • species breaks the molecular bonds. Many more studies are reported in the literature. Table 2.3 presents the optimal operating conditions used in these studies and the maximum removals achieved. Table 2.3 – Studies on the treatment of dye solutions and textile effluents by Fenton’s reaction. Dye solution or Effluent type Optimal Operating Conditions Efficiencies (%) Comments Reference Real effluent of acetate and polyester deying pH = 5 [FeSO 4 ] = 500 mg/L [H 2 O 2 ] = 300 mg/L Color = 94 COD = 96 Azbar et al. [2004] Reactive Black 5 dye solution pH = 3 T= 40 ºC [dye] = 100 mg/L [FeSO 4 ] = 100 mg/L [H 2 O 2 ] = 400 mg/L Color = 99 COD = 71 Meriç et al. [2004] Reactive Black 5 dye solution pH = 3 T= 40 ºC [dye] = 200 mg/L [FeSO 4 ] = 225 mg/L [H 2 O 2 ] = 1000 mg/L Color = 99 COD = 84 Meriç et al. [2004] Reactive Orange 4 dye solution pH = 5 [Fe 2+ ] = 0.075 mM [H 2 O 2 ] = 15 mM Dye = 97 Muriganandham and Swaminathan, [2004] Blue Suncron RD400 dye solution [Fe 2+ ] = 0.38 mM [H 2 O 2 ] = 2.48 mM COD = 60 Dye = 90 Kim et al. [2004] Yellow Suncron 3GE-200 dye solution [Fe 2+ ] = 0.41 mM [H 2 O 2 ] = 1.91 mM COD = 48 Dye = 90 Kim et al. [2004] Blue Suncron P-3R dye solution [Fe 2+ ] = 1.61 mM [H 2 O 2 ] = 4.41 mM COD = 80 Dye = 90 Kim et al. [2004] Yellow Suncron E4R-H dye solution [Fe 2+ ] = 0.23 mM [H 2 O 2 ] = 1.15 mM COD = 70 Dye = 90 Kim et al. [2004] Part I 33 Table 2.3 – Studies on the treatment of dye solutions and textile effluents by Fenton’s reaction. (cont.) Dye solution or Effluent type Optimal Operating Conditions Efficiencies (%) Comments Reference Orange II dye pH = 3 T= 29 ºC t = 120 min [H 2 O 2 ] = 10 mM Fe 2+: H 2 O 2 ratio (w/w) = 0.08 Color = 100 Ramirez et al. [2005] Orange II dye pH = 3 T= 50 ºC t = 120 min [H 2 O 2 ] = 13.8 mM Fe 2+: H 2 O 2 ratio (w/w) = 0.05 TOC = 71 Ramirez et al. [2005] Reactive Black 5 pH = 5 t = 120 min [dye] 0 = 1.0x10 -4 M [Fe 2+ ] = 1.5x10 -4 M [H 2 O 2 ] 0 = 7.3x10 -4 M Color = 98 TOC = 22 Lucas and Peres [2006] Synthetic Dyeing effluent containing acid dyes pH = 3 t = 30 min [Fe 2+ ] = 10 mM [H 2 O 2 ] = 30 mM Color = 92 COD = 24 Low toxicity to bacteria from activated sludge Alaton and Teksoy [2007] Remazol Turquoise Blue G-133 dye solution pH = 3 t = 45 min [Fe 2+ ] = 25 mg/L [H 2 O 2 ] = 50 mg/L Color = 99 k = 0,0102 L mg -1 min -1 Bali and Karagozoglu [2007] Acid Yellow 23 dye solution pH = 3 [Fe 2+ ] = 0.1 mmol [H 2 O 2 ] = 500 mg/L Color ~ 100 Modirshahla et al. [2007] Real effluent from polyethylene fibers processing pH = 3 t = 24 h [Fe 2+ ] = 40 mg/L [H 2 O 2 ] = 30 mg/L Color = 72 COD = 45 BOD 5 = 60 TOC = 40 BOD 5 :COD ≤ 0.15 (after treatment) Papadopoulos et al. [2007] Amido Black 10B dye solution pH = 3.5 [dye] 0 = 50 mg/L [Fe 2+ ] 0 = 0.025 mM [H 2 O 2 ] 0 = 0.50 mM Dye = 99 Sun et al. [2007] Chapter 2 – State of the Art 34 Table 2.3 – Studies on the treatment of dye solutions and textile effluents by Fenton’s reaction. (cont.) Dye solution or Effluent type Optimal Operating Conditions Efficiencies (%) Comments Reference Procion Red HEXL gran dye solution pH = 3.5 t = 120 min [dye] = 100 mg/L T= 73.6 ºC [Fe 2+ ] = 0.12 mM [H 2 O 2 ] = 2.9 mM Color = ~100 TOC = 58 Rodrigues [2007] Wastewater from acrylic fiber manufacturing pH = 3 t = 2 h [Fe 2+ ] = 300 mg/L [H 2 O 2 ] = 500 mg/L COD = 66 BOD 5 :COD = 0.5 (after treatment) Li et al. [2012] Real textile effluent pH = 6.6 T = 35 ºC [FeSO 4 ] = 0.75 g/L [H 2 O 2 ] = 15 g/L Color = 98 COD = 39 BOD 5 :COD = 0.45 (after treatment) Wu and Wang [2012] Real dry-spun acrylic fiber effluent pH = 3 T = 30 ºC t = 120 min [Fe 2+ ] = 20 mM [H 2 O 2 ] = 90 mM COD = 47 TOC = 35 BOD 5 :COD = 0.69 (after treatment) Wei et al. [2013] Real dry-spun acrylic fiber effluent pH = 3 T = 50 ºC t = 120 min [Fe 2+ ] = 20 mM [H 2 O 2 ] = 90 mM k = 0.265 min -1 Wei et al. [2013] 2.3.2 Textile Wastewater Treatment by Integration of Homogeneous Fenton’s Oxidation with Sequencing Batch Reactor Treatability studies of textile effluents by Fenton´s oxidation combined with sequencing batch reactor (SBR) are succinctly described in this section. Fongsatitkul et al. [2004] evaluated the integration of Fenton’s reagent with biological oxidation in SBR for treating wastewater generated in the textile industry. Experimental conditions were pH 3, T = 28-30 °C, reaction time about 30 minutes and total dose of reagents between 25 mg/L and 300 mg/L (FeSO 4 .7H 2 O and H 2 O 2 - 1:1 molar ratio). Part I 35 Maximum color and COD removals (~ 70% and ~ 30%, respectively) were achieved for reagent doses of 75 mg/L. To increase the efficiency of organic matter removal, the authors tested the combination Fenton’s oxidation plus SBR. The biological treatment was performed at pH 7, the operating cycle of SBR was 24 hours, distributed as follows: 4 hours feeding, 2 hours anoxic, 4 hours aerobic, 7 hours anoxic, 4 hours aerobic, 1.5 hours sedimentation, 0.5 hours draw and 1 hour sludge removal. The global efficiency was given by: 90% COD removal, ~ 80% maximum color removal, 81 phosphorus removal and 92% KTN removal. Afterwards the treatability of the effluent by the combination of SBR with chemical oxidation was also investigated. The SBR was operated under the same conditions described above and was fed for 50 days. The biological process was able to remove ~ 80% COD, ~50% color, ~ 82% KTN and ~ 58% total phosphorus. Then the biologically treated effluent was subjected to chemical oxidation, after adjusting the pH to 3. The dose of reagent varied in the range 25-200 mg/L. Removals increased with the dose of reagent, reaching 27 and 60% for COD and color, respectively, using 200 mg/L of reagent. The combination SBR plus Fenton’s oxidation led to overall efficiencies of 87% for COD, 68% for color, 91% for KTN and 80% for total phosphorus.The frist combination of processes (Fenton’s oxidation followed by SBR) yielded better results, because the pretreatment increased the biodegradability of the effluent to be subjected to biological treatment. More recently Lodha and Chaudhari [2007] evaluated the treatability of azo dyes (Reactive Black 5 dye - RB5 - Reactive Blue 13 - RB13 - and Acid Orange 7 - AO7) solutions. The Fenton process was optimized by varying the pH (2-7), [H 2 O 2 ] (between 25 and 150 mg/L) and [Fe 2+ ] (from 5 to 50 mg/L) and setting the reaction time within 30 minutes. The conditions that maximized color (>97% for all dyes tested) and COD (63, 89 and 68% for RB5, RB13 and AO7, respectively) removals were pH = 3, [Fe 2+ ] = 15 mg/L and [H 2 O 2 ] = 50 mg/L. For the biological treatment, the biomass was previously acclimatized. Thus, for a period of 20 days, the SBR was fed with 0.5 L of a solution containing 0.4 g of dextrose, alternating the next day with 0.5 L of pretreated effluent. The solids content in the SBR was maintained in 3000 mg MLSS/L. The SBR reached steady state after 40 days (20 days of acclimatization and 20 fed with pre-oxidized effluent), achieving COD removals of 82, 89 and 84% for RB5, RB13 and AO7 dyes, respectively. An integrated process (chemical oxidation with Fenton's reagent followed by biological oxidation) was also performed yielding total decolorization (> 99% for all dyes) and higher COD removals (93, 99 and 95% for RB5, RB13 and AO7, respectively). Chapter 2 – State of the Art 36 More studies can be found in the literature regarding the treatment of textile effluents or dye solutions by the combination of Fenton´s reaction with SBR. Table 2.4 briefly presents the best operating conditions for both processes and the overall efficiencies achieved. Table 2.4 – Studies on the integration Fenton’s reaction with SBR. Dye solution or Effluent type Operatory Conditions in Fenton Operatory Conditions in SBR Overall Eficiencies (%) Comments Reference Reactive Black 5 solution pH = 3 T = 25-30 ºC [Fe 2+ ] = 1.05 mM [H 2 O 2 ] = 72 mM t feed = 20 days HRT = 96 h SRT = 45 days COD = 82 The SBR was previously acclimated by feeding dextrose solution Tanatak and Chaudhari [2007] Reactive Blue 13 solution pH = 3 T = 25-30 ºC [Fe 2+ ] = 1.05 mM [H 2 O 2 ] = 72 mM t feed = 20 days HRT = 96 h SRT = 45 days COD = 86 The SBR was previously acclimated by feeding dextrose solution Tanatak and Chaudhari [2007] Acid Orange 7 solution pH = 3 T = 25-30 ºC [Fe 2+ ] = 1.05 mM [H 2 O 2 ] = 72 mM t feed = 20 days HRT = 96 h SRT = 45 days COD = 78 The SBR was previously acclimated by feeding dextrose solution Tanatak and Chaudhari [2007] Synthetic cotton deying effluent pH = 3.5 T = 73.6 ºC [Fe 2+ ] = 11 mM [H 2 O 2 ] = 305 mM 1.1 h feed 6 h reaction 3.5 h sedimentation 0.9 h supernatant discharge [O 2 ] ~3 mg/L pH ~7 T ~25 ºC [VSS] ~5 g/L BOD 5 = 96 COD = 90 Color = 97 Rodrigues [2007] 2.4 Photo-Fenton Process The photo-Fenton process is based on principles that are common to the dark Fenton one, namely the generation of extremely reactive hydroxyl radicals (that will unselectively Part I 37 attack the organic compounds) by breaking hydrogen peroxide molecules, in acidic medium, making use of a catalyst like ferrous ion (Equation 2.6) [Walling, 1975], but with simultaneous use of ultra-violet/visible radiation. Thus, the photo-Fenton process is faster and enables reducing the consumption of chemicals as the hydroxyl radicals generation occurs by three different mechanisms: i) the decomposition of hydrogen peroxide by the Fe 2+ catalyst (Equation 2.6); ii) the incidence of ultraviolet radiation, with λ<360-365 nm, decomposes the hydrogen peroxide into hydroxyl radicals (Equation 2.7) [Galvez and Rodriguez, 2003]; and iii) by using radiation with wavelengths in the range 290 <λ< 410 nm [Sun and Pignatello, 1993], there is the additional production of HO • radicals upon Fe 2+ regeneration either by Equation 2.8 or by photolysis of iron (III) hydroxides (Equation 2.9); finally, Equation 2.10 still refers to Fe 2+ regeneration by photolysis of complexes formed between the organic compounds or their intermediates with Fe 3+ [Galvez and Rodriguez, 2003; Morais, 2005; Huang et al., 2008]. The regeneration of Fe 2+ species by several reactions is another reason for the faster rate of the photo-Fenton process as compared to the dark one, where catalyst regeneration is commonly rate-limiting. Fe 2+ + H 2 O 2 → Fe 3+ + HO • + OH − (2.6) H 2 O 2 + hν → 2HO • (2.7) Fe 3+ + H 2 O 2 + hν → Fe 2+ + HO • + H + (2.8) Fe(OH) 2+ + hν → Fe 2+ + HO • (2.9) [Fe(RCO 2 )] 2+ + hν → Fe 2+ + CO 2 + R • (R= organic compound) (2.10) The Fe(OH) 2+ complex is predominant under acidic conditions (pH in the range 2-3 [Torrades et al., 2004]), and plays an important role in the photo-Fenton process since it is the compound with greater ability to generate hydroxyl radicals by absorbing UV/visible radiation. The photolysis of hydrogen peroxide (Equation 2.7), which has low absorptivity (19.6 M -1 cm -1 at 254 nm [Engwall et al., 1998]), has a limited contribution towards the formation of radicals when iron complexes are present in solution. The photo-Fenton process is influenced by many variables, such as pH, hydrogen peroxide concentration, ferrous ion concentration and radiation intensity (and nature). At pH > 6 the Fe 3+ forms insoluble oxides [Pérez et al., 2002]. In very acidic pH values the complex Fe(OH) 2+ is present in a reduced amount, and the two more photo reactive Chapter 2 – State of the Art 38 compounds (Fe(OH)(H 2 O) 52+ and Fe(OH) 2 (H 2 O) 4+ ) are present in smaller quantities to generate the radicals and regenerate the catalyst [Morais, 2005; Nogueira, 2007], however the Fe(H 2 O) 63+ species is present in greater amount but it has lower absorptivity, which limits the absortion of radiation [Nogueira et al., 2007]. Moreover, pH < 2.5 allows to occur the scavenging reaction between the hydroxyl radical and H + (Equation 2.11) [Nogueira et al., 2007]: HO • + H + + e - →H 2 O (2.11) For these reasons, optimum pH values in the range 2-3 have been pointed out [Pignatello, 1992; Kim, 1997; Wu et al., 1999; Elmolla and Chaudhuri, 2009]. Actually, in this range increased amounts of photo reactive species (Fe 3+ and Fe(OH) 2+ ) are present in solution. For removal of dyes some authors have suggested pH values of 3-5 [Kang et al., 2000; Liu et al., 2007; Modirshahla et al., 2007]. The amount of catalyst to be used must be determined and optimized, since it depends on the nature of the effluent to be treated. Nonetheless, it is not advisable to use an excess of Fe 2+ because this generates turbidity which hinders the absorption of the radiation and, on the other hand, as in dark Fenton, occurs the scavenging reaction of hydroxyl radicals with the excess Fe 2+ (Equation 2.4). The pollutant removal is related to the amount of hydrogen peroxide, thus it is necessary to determine the optimum dose of reagent considering that: i) when its concentration is low the oxidation degree is low and there is the possible formation of undesirable intermediate compounds, ii) its excess reacts with hydroxyl radicals generating HO 2. radicals with lower oxidative potential and iii) an excess is required to compensate the decomposition into water and oxygen and other parallel /undesirable reactions. The radiation intensity or photonic flux is related to the lamp power i.e. the capacity to emit photons. In general, an increase in the radiation intensity leads to an increase in the reaction rate, hence an increased degradation of organic compounds. According to Malato et al. [2002], the advantages of the photo-Fenton process, compared to other photochemical techniques, are the operation at UV or near UV wavelengths (300400 nm), the sensitivity to light up to wavelengts ≤ 600 nm, which makes possible the use of solar radiation, the light penetration is deeper and the contact between pollutant and oxidizing agent is intimate, because of the homogenous phase. The major disadvantages Part I 39 of this process are associated with the use of low pH (<4) to obtain the maximum efficiency and the generation of chemical sludge containing iron. 2.4.1 Textile Wastewater Treatment by Homogeneous Photo-Fenton Process A lot of studies can be found in the literature using the photo-Fenton process for dyes removal in aqueous solution, as well as in the treatment of effluents from the textile industry. A brief description of some of these studies is presented below. Kang et al. [2000] evaluated the removal of color from a synthetic textile dyeing effluent (containing 100 mg/L of polyvinyl alcohol – PVA – and 100 mg/L of Reactive R94H dye) by the photo-Fenton process. Under optimal conditions (pH = 4, [H 2 O 2 ] = 100 mg/L, [Fe 2+ ] = 20 mg/L, lamp power = 64 W and t = 30 min) the authors obtained 95% color removal. Subsequently, the effect of the PVA concentration was evaluated by varying its concentration (COD between 200 to 620 mg/L) and it was found that the increase of COD showed no effect on color removal. Comparing photo-Fenton at pH of 4 and 7 with Fenton at pH 4 and photolysis at pH 4, it was observed that photo-Fenton process at pH 4 led to a higher removal (93%) for a reaction time of 30 min, followed by photolysis (82% color removal in the same period), then photo-Fenton at pH 7 (73% color removal) and finally dark Fenton at pH 4 (64% color removal). Pérez et al. [2002] studied the treatability of a real textile effluent by the photo-Fenton process. The authors started the study by evaluating the effect of Fe 2+ , H 2 O 2 and combination of the two reagents. Varying the temperature (25-70 °C) higher removals of TOC were achieved at 70 ºC. The effect of ferrous ion (up to 400 mg/ L) and hydrogen peroxide (up to 10 g/L), setting the pH at 3 and temperature at 40 °C, was also analyzed. Maximum TOC removal (70% after 2 hours of reaction) was achieved when using 100 mg/L of Fe 2+ and H 2 O 2 between 2.5 and 5 g/L. At these operating conditions, the effect of the type of radiation (light from luminescent black lamp of 6 W, sunlight and xenon lamp of 250 W) was assessed. For the first 60 min of reaction TOC removal was high when using xenon and solar radiation, but for t>60 min the luminescent black lamp showed better removal efficiency. The authors state that an intense irradiation favors the exhaustion of Chapter 2 – State of the Art 46 (anaerobic/aerobic SBR). The 1 st system operated during 48 h per cycle, comprising several minutes for feeding the wastewater, 20 h-anaerobic reaction, 4h-settle, 20 haerobic reaction, 4 h-settlle/draw. In the 2 nd system the anaerobic and aerobic reaction occurred in separated reactors, and each cycle of 48 h was divided as follows: several minutes for feeding the effluent into the anaerobic reactor, 20 h-anaerobic reaction, 2 hsettle and 2 h to draw the supernatant that fed the aerobic reactor for 2 h, 20 h of reaction and 4 h-settle/draw. The maximum decolorization (80.8% after 36 cycles) was obtained when anaerobic and aerobic reactions occurred separately (2 nd system). Lourenço et al. [2001] also studied the degradation of Remazol Brilliant Violet 5R and Remazol Black B dyes by AA-SBR. For Remazol Brilliant Violet 5R the authors obtained 90% dye removal when operating 24 h per cycle (50 min-fill, 11 h-anaerobic reaction, 10 h-aeration, 60 min-settle, 55 min-draw and 15 min-idle) and 10 days of SRT (sludge retention time), while for Remazol Black B reached 75% of dye removal using 24 h per cycle (53 min-fill, 11 h-anaerobic reaction, 10 h-aeration, 50 min-settle, 65 min-draw and 10 min-idle) and 15 days of SRT. Table 2.6 presents optimal operating conditions and efficiencies attained in other research works concerning the treatment of dye solutions and textile effluents in SBR. Table 2.6 – Studies on the treatability of dye solutions and textile effluents by SBR. Dye solution or Effluent type Optimal Operating Conditions Efficiencies (%) Comments Reference Simulated effluent containing Remazol Red RR dye 5 min fill 12 h anaerobic reaction 11 h reaction 30 min settle 10 min draw [Dye] = 60 mg/L [COD] 0 = 800 mg/L SRT = 15 days Color = 95 COD = 70 Addition of phosphates, sulfates and glucose to the effluent Kapdan and Oztuk [2005] Synthetic wastewater containing Vat Yellow 1 dye 1 h fill (with aeration) 19 h react 3 h settle 0.5 h draw 0.5 h idle (in anoxic conditions) HRT = 3 days [VSS] = 2000 mg MLSS/L Color = 99 COD = 97 BOD 5 = 99 KTN = 93 Addition of urea, glucose, KH 2 PO 4 and other nutrients to the effluent Siriamuntapiboon et al. [2006] Part I 47 Table 2.6 – Studies on the treatability of dye solutions and textile effluents by SBR (cont.). Dye or Effluent type Optimal Operating Conditions Efficiencies (%) Comments Reference Real wastewater plus 0.89 g/L of glucose 1 h fill (with aeration) 19 h react 3 h settle 0.5 h draw 0.5 h idle (in anoxic conditions) Color = 75 COD = 71 BOD 5 = 97 KTN = 63 Siriamuntapiboon et al. [2006] Synthetic wastewater containing Acid Black 210 dye 30 min fill 23 h aeration with recirculation 15 min settle 15 min draw Color = 100 COD = 92 Addition of glucose and nutrients to the wastewater Mohan et al. [2007] Simulated effluent containing Remazol Brilliant Violet 5R dye 3 min fill 12 h anaerobic reaction 11.9 h aerobic reaction 3 min draw Color = 72 COD = 75 Benzene based aromatic amines = 92 Addition of glucose and nutrients to the dye solution Çinar et al. [2008] Synthetic wastewater containing Reactive Red 195 dye [Dye] = 40 mg/L [COD] 0 = 800 mg/L SRT = 50 days 24 h per cycle Color > 90 COD > 90 Addition of nutrients and acetic acid to the wastewater k color in anaerobic reaction = 0.135 h -1 k COD in anaerobic reaction = 0.043 h -1 Farabegoli et al. [2010] Synthetic Wastewater containing Reactive Blue Bezaktiv S-GLD 150 dye 15 min fill 23 h aerobic reaction 30 min settle 15 min draw SRT = 30 days Volumetric dye rate 15 g/(m 3 d) Color = 8897 COD = 9598 Addition of glucose, (NH 4 ) 2 SO 4 and KH 2 PO 4 to the dye solution The inocula were acclimatized during 30 days under aerobic conditions Khouni et al. [2011 b)] Simulated effluent containing Acid Black 10B dye 15 min fill 2820 min aeration reaction with recirculation 30 min settle 15 min decant Color after 18 cycles = 67 COD after 10 cycles = 88 Addition of glucose and nutrients to the effluent Mohan et al. [2012] Other authors [Kapdan and Oztekin, 2006] evaluated the effect of the anaerobic stage time (2-19h) and initial COD concentration (400-1800 mg/L) on the performance of a SBR system treating a simulated wastewater containing Remazol Red RR dye, phosphates, Chapter 2 – State of the Art 48 sulfates and glucose. The color removal, in the anaerobic phase, was completed in the first 4-6 h, achieving 90% decolorization. Operating the aerobic phase for 19-20 h, 80% COD removal was achieved, while 50% was reached in the anaerobic stage. The aerobic stage was efficient even when reducing the period of the anaerobic stage (2-4 h). Finally, Vaigan et al. [2009] evaluated the effect of Brill Blue KN-R dye concentration in the performance of SBR. The reactor operated during 36 cycles (5 for sludge acclimatization and 31 for normal operation) with 24 h per cycle comprising 2 min to fill, 22.5 h for aerated reaction, 1 h settling, 2 min of draw and 25 min for idle. Color removal decreased from 57.0% to 31.0% when the dye concentration increased from 20 to 40 mg/L, however COD removal was practically constant (~97%) for all concentrations. 2.5.2 Textile Wastewater Treatment by Combination of SBR and Other Techniques In this section are presented some studies concerning the treatability of simulated effluents containing dyes or real textile wastewaters by biological oxidation in SBR integrated with other treatment methods. Krull and Hempel [2001] evaluated the color and COD removals and toxicity reduction of dye-house liquor by combining SBR with ozonation. After the chemical treatment the effluent was introduced into the SBR and subjected to aerobic degradation. By integrating the two processes the authors obtained 90 and 98% of COD and color removals, respectively, and toxicity was reduced by 99%, as determined by bioluminescence tests. Other authors [Zuriaga-Agusti et al., 2010] evaluated the treatment of a simulated textile wastewater (containing 20 mg/L of Remazol Yellow RR, Remazol Red RR and Remazol Blue RR, glucose and nutrients) by combining biological oxidation in SBR with nanofiltration. The SBR was operated at 2.5 days of HRT and 20 h per cycle comprising 0.2 h-fill, 9 h-anaerobic react, 8 h-aerobic react, 2 h-settle, 0.3 h-draw and 0.5 h-idle. In the first 55 cycles the SBR was fed with synthetic wastewater and removals of 80 to 90% were achieved for Red and Blue dyes and 70 to 80% for Yellow dye. Afterwards the SBR was fed with three different mixtures: i) 4.0 L of synthetic textile wastewater (STW) and 1.0 L of nanofiltration rejection (NFR), ii) 3.5 L of STW and 1.5 L of NFR and iii) 2.5 L of Part I 49 both effluents. It was found that higher amounts of NFR in the feed stream caused a more marked decay in the efficiency of dye removal, due to conductivity increase. Blanco et al. [2012] studied the applicability of Fenton´s reaction and combination of SBR with Fenton’s reagent for treating a real textile wastewater. In the Fenton process alone, the authors evaluated the effect of H 2 O 2 dose (1650-4950 ppm), Fe 2+ dose (109-540 ppm) and temperature (25-35 ºC) and achieved maximum TOC removal (64%) and Escherichia coli reduction (>99%) in the following conditions: 25 ºC, 3, 1650 mg/L and 216 mg/L for T, pH, [H 2 O 2 ] and [Fe 2+ ], respectively. The treatment in SBR alone was carried out after pH adjustment to 6.5-7.5, addition of nutrients, oxygen at 3 mgO 2 /L and T=25 ºC. 75% TOC removal was reached for HRT=1 day. Finally, using the combination of biological oxidation followed by Fenton process (pH=3, [H 2 O 2 ]=1518 mg/L and [Fe 2+ ]=66.5 mg/L) remarkable removal efficiencies of 92 and 99% for TOC and E. coli, respectively, were achieved, showing the interest in integrating both processes. Additional studies focused on the combination of SBR with adsorption by GAC are reported in the literature and summarized in Table 2.7, where the operating conditions and global removal efficiencies are also presented. Table 2.7 – Studies on the integration of SBR with other processes for treating dye solutions and textile effluents. Dye solution or Effluent type Operating Conditions in SBR Other Process Overall Efficiencies (%) Comments Reference Disperse Red 60 dye 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle HRT = 3 days [dye] = 80 mg/L Granular Activated Carbon BOD 5 = 97 COD = 97 KTN = 90 Siriamunta piboon and Srisornsak [2007] Real wastewater containing Disperse Red 60 and Disperse Blue 60 dyes 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle SRT = 67 days HRT = 5 days Granular Activated Carbon Color = 95 BOD 5 = 94 COD = 94 KTN = 59 Addition of glucose to the wastewater No production of excess sludge Siriamunta piboon and Srisornsak [2007] Chapter 2 – State of the Art 50 Table 2.7 – Studies on the integration of SBR with other processes for treating dye solutions and textile effluents (cont.). Dye solution or Effluent type Operating Conditions in SBR Other Process Overall Efficiencies (%) Comments Reference Direct Red 23 and Direct Blue 201 dyes solutions 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle Granular Activated Carbon BOD 5 , COD and KTN in the order 89-99 Sirianuntap boon et al. [2007] Real wastewater containing Direct Red 23 and Direct Blue 201 dyes 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle Granular Activated Carbon Color = 76 BOD 5 = 84 COD = 86 KTN = 68 Addition of glucose to the wastewater No production of excess sludge Sirianuntap boon et al. [2007] Simulated effluent containing Direct Blue 201 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle HRT = 7.5 days SRT = 22 days [VSS] = 3000 mg MLSS/L Granular Activated Carbon BOD 5 , COD and KTN >93 Addition of urea, glucose and nutrients to the effluent Sirianuntap boon and Sansak [2007] Simulated effluent containing Direct Red 23 dye 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle HRT = 7.5 days SRT = 22 days [VSS] = 3000 mg MLSS/L Granular Activated Carbon BOD 5 , COD and KTN >93 Addition of urea, glucose and nutrients to the effluent Sirianuntap boon and Sansak [2007] Real effluent 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle SRT = 28 days Granular Activated Carbon BOD 5 , COD and KTN >93 Addition of glucose to the effluent Sirianuntap boon and Sansak [2007 Real effluent 1 h fill 19 h reaction 3 h settle 0.5 h draw 0.5 h idle SRT = 28 days Granular Activated Carbon BOD 5 , COD and KTN >93 Addition of rice wastewater to the effluent Sirianuntap boon and Sansak [2007 Part I 51 2.6 References Al-Ani, Y.; Li, Y. 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Notrogen removal and heavy metals in leachate treatament using SBR technology. Journal of Hazardous Materials, 174, 679-686. Chapter 3 Materials and Methods Part II 65 3 Materials and Methods 3.1 Introduction This part of the thesis regards the preparation and characterization of synthetic effluents as well as the characterization of a real cotton dyeing effluent. A brief description of the analytical methods and experimental procedures is also presented. 3.2 Textile Dyeing Wastewaters 3.2.1 Simulated Textile Dyeing Wastewaters Once the treatability of a given effluent depends on the constituents present therein and their respective concentration, this study started by establishing a contact with the textile dyeing company Erfoc – Acabamentos Têxteis S.A. (located in Famalicão) – so as to collect information regarding the amounts of dyes and auxiliary products used in dyebaths of synthetic (polyester and acrylic) and natural (cotton) fibers and the degree of fixation of each chemical on the fibers. This way one could predict the concentration of each individual chemical in the final (and complex) effluent and prepare the corresponding simulated wastewaters. 3.2.1.1 Dyes Two disperse (Dianix Blue K-FBL and Dianix Orange K3G), one basic (Astrazon Blue FGGL 03 300%) and two reactive (Procion Yellow H-EXL gran and Procion Deep Red HEXL gran) dyes were selected for the preparation of the simulated effluents, as they are commonly used for dyeing polyester, acrylic and cotton fibers, respectively. Table 3.1 shows the structures (available from the manufacturer) of the dyes present in each effluent as well as some other characteristics such as the dye class and the experimentally determined wavelength of maximum absorbance in the visible region. The chemical structure and generic name of the Procion deep red H-EXL gran dye is not Chapter 3 – Materials and Methods 66 presented as this dye is a mixture of two dyes (reactive yellow 138:1 and another reactive azo dye). These dyes were kindly provided by DyStar-Anilinas Têxteis Unipessoal Lda. The selection of these dyes also took into account the following aspects: i) the reactive dyes, which are used in large amounts for dyeing fibers in Portugal, deserve special attention because of their low degree of fixation on the fibers, so that considerable quantities are rejected and will be present in the effluent; furthermore, some reactive dyes are not easily removed by conventional processes, such as biological treatment and coagulation/flocculation using inorganic coagulants; ii) the basic dyes exhibit an increase in consumption due to their high tintorial value and increased consumption of acrylic fibers; iii) the consumption of disperse dyes has been rising following the increase in demand for polyester fibers. 3.2.1.2 Auxiliary Chemicals The dyeing auxiliaries were also supplied by DyStar – Anilinas Têxteis Unip. Lda. Table 3.2 presents the auxiliary products used in the preparation of the dyebaths for each fiber considered and their main characteristics. Table 3.1Characteristics of the dyes present in each simulated effluent. Commercial name Generic name Dianix Blue K-FBL Disperse Blue 56 Dianix Orange K3G Disperse Orange 30 Astrazon Blue FGGL 300% 03 Basic Blue 41 Procion Yellow H-EXL gran Reactive Yellow 138:1 Procion Deep Red H-EXL gran n.a. * * not available. Characteristics of the dyes present in each simulated effluent. Generic name Class Molar mass (g/mol) Chemical structure Polyester effluent Disperse Blue 56 Anthraquinone 304.14 Disperse Orange 30 Azo 450.27 Acrylic effluent Basic Blue 41 Azo 482.57 Cotton effluent Reactive Yellow 138:1 Azo n.a. * n.a. Azo n.a. * n.a. Part II 67 Chemical structure λ max (nm) 600 450 610 n.a. * 420 n.a. * 520 Chapter 3 – Materials and Methods 68 Table 3.2 - General characteristics of the auxiliary products used for dyeing polyester, acrylic and cotton fibers. Comercial name Dyeing step Function Chemical characteristic Polyester effluent Adranol NL Fiber preparation Anti-oil - Antibacol R Fiber preparation/Dyeing Anti-crease - Trisodium phosphate Fiber preparation Electrolyte Salt Sera Gal PLP Dyeing Equalizing/dispersant Alkyl polyglycol ether solution Ammonium sulfate Dyeing Electrolyte Salt Acetic acid Dyeing Acid generator Acid Sodium hydroxide 32% (w/v) Washing Alkaline system Base Sodium hydrosulfite Washing Reducer system Reducer Acrylic effluent Sera Con N-VS Dyeing Acid generator Carboxylic acid ester solution Sera Sperse M-IW Dyeing Dispersant Alkyl polyglycol ether solution Sera Tard A-AS Dyeing Retarder N-alkyl-N, Ndimethylbenzylammonium Sodium sulfate Dyeing Electrolyte Salt Sera Lube M-CF Dyeing Anti-crease/lubricant Polymeric amides solution Cotton effluent Mouillant BG/JT Fiber preparation Anti-oil Composition based in aliphatic ethoxylates Anticassure BG/BD Fiber preparation Anti-crease Acryamide aqueous solution Sodium hydroxide 50% (w/v) Fiber preparation Alkaline system Base Hydrogen peroxide 200 vol. Fiber preparation Oxidizing the dye Oxidant reagent Acetic acid Fiber preparation Acid generator Acid Zerox Fiber preparation Hydrogen peroxide neutralizer Catalase Enzyme BG/FB Fiber preparation Bleaching Fungal cellulase Sequion M150 Dyeing Water corrector Composed by phosphanates/carboxylates Sodium chloride Dyeing Electrolyte Electrolyte Sodium carbonate Dyeing Alkalyne system Base Sandozin NRW LIQ ALT C Washing Detergent Polyethylene glycol isotridecyl ether Part II 69 3.2.1.3 Preparation of the Simulated Textile Dyeing Effluents The effluents were prepared taking into account that for every process there are several stages, namely fiber preparation, dyeing and washing (although the fiber preparation stage is not used in acrylic dyeing). Moreover, it is worth mentioning that in each particular case different volumes of water and chemicals are employed along the process, as shown in Table 3.3, and that the ratio between the amount of fiber to be dyed and the water used in the bath was assumed to be 1:10 (kg:L). Finally, the percentage of these products unfixed in the textile fibers (and therefore released into the water) should be also taken into account. This information was provided by a dye-house (Erfoc-Acabamentos Têxteis S.A. - Famalicão, Portugal) and by DyStar Anilinas Têxteis, Unip Ltd (Portugal), and is summarized in Table 3.3 along with the estimated concentration of each reagent in the simulatedl effluents (polyester, acrylic and cotton), which was based in the total volume of water employed in all stages. Figures 3.1 to 3.3 show the temperature profiles of the respective dyeing processes and the moment of addition of each component. Chapter 3 – Materials and Methods 70 Table 3.3 - Estimated concentration of each component in the polyester, acrylic or cotton simulated effluents. Chemical Dyeing stage Dyeing stage Concentration Rejection** Concentration in the final effluent from each step Concentration in the global effluent Polyester effluent Adranol NL Fiber preparation 1 g/L 100% 1 g/L 0.33 g/L Antibacol R Fiber preparation 1 g/L 100% 1 g/L 0.33 g/L Trissodic phosphate Fiber preparation 1 g/L 90% 0.9 g/L 0.30 g/L Sera Gal PLP Dyeing 0.5 g/L 100% 0.5 g/L 0.17 g/L Antibacol R Dyeing 1 g/L 100% 1 g/L 0.33 g/L Ammonium sulfate Dyeing 2 g/L 90% 1.8 g/L 0.60 g/L Acetic acid Dyeing 0.5 g/L 100% 0.5 g/L 0.17 g/L Dianix Blue KFBL Dyeing 0.71%* 5% 0.036 g/L 0.012 g/L Dianix Orange K3G Dyeing 1.2%* 5% 0.06 g/L 0.02 g/L Sodium hydroxide 32% (w/v) Washing 3 g/L 100% 3 g/L 1.0 g/L Sodium hydrosulfite Washing 3 g/L 90% 2.7 g/L 0.90 g/L Acrylic effluent Sera con N-VS Dyeing 0.4 mL/L 100% 0.4 mL/L 0.13 mL/L Sera sperse M-IW Dyeing 0.5 g/L 100% 0.5 g/L 0.17 g/L Sera tard A-AS Dyeing 1 g/L 100% 1 g/L 0.33 g/L Sodium sulfate Dyeing 3 g/L 90% 2.7 g/L 0.90 g/L Sera lube M-CF Dyeing 2 g/L 100% 2 g/L 0.67 g/L Astrazon Blue FGGL 300% 03 Dyeing 1.5%* 5% 0.025 g/L 0.008 g/L Cotton effluent Mouillant BG/JT Fiber preparation 0.7 mL/L 90% 0.21 mL/L 0.09 mL/L Anticassure BG/BD Fiber preparation 0.5 mL/L 90% 0.15 mL/L 0.06 mL/L Part II 71 Table 3.3 - Estimated concentration of each component in the polyester, acrylic or cotton simulated effluents. (cont.) Chemical Dyeing stage Dyeing stage Concentration Rejection** Concentration in the final effluent from each step Concentration in the global effluent Cotton effluent Sodium hydroxide 50% (w/v) Fiber preparation 4 mL/L 100% 1.3 mL/L 0.57 mL/L Hydrogen peroxide 200 vol. Fiber preparation 1.5 mL/L 85% 0.4 mL/L 0.18 mL/L Acetic acid Fiber preparation 0.8 mL/L 100% 0.26 mL/L 0.11 mL/L Zerox Fiber preparation 0.6 mL/L 90% 0.18 mL/L 0.08 mL/L Enzyme BG/FB Fiber preparation 0.4 mL/L 90% 0.12 mL/L 0.05 mL/L Sequion M150 Dyeing 1 mL/L 100% 1 mL/L 0.14 mL/L Sodium chloride Dyeing 9 g/L 90% 8.1 g/L 1.16 g/L Sodium carbonate Dyeing 20 g/L 90% 18 g/L 2.6 g/L Procion Yellow H-EXL gran Dyeing 0.45%* 10% 0.045 g/L 0.006 g/L Procion Deep Red H-EXL gran Dyeing 2.8 %* 10% 0.28 g/L 0.04 g/L Sandozin NRW LIQ ALT C Washing 0.9 mL/L 90% 0.27 mL/L 0.12 mL/L * w dye/w fiber; ** Percentage of dyes and auxiliary products not fixed by the fibers. Chapter 3 – Materials and Methods 78 3.3.4 Chemical Oxygen Demand The determination of the COD was performed according to method 5220 B [APHA, 1998], which quantifies the K 2 Cr 2 O 7 reduction by oxidizable organic and inorganic compounds in an open reflux digester (G.VITTADINI Record/6Test digester), at 150 °C for 2 hours. The remaining dichromate was determined by titration with ammonium iron sulphate. COD was also determined by the closed reflux method (Method 5220 D [APHA, 1998]), at 150 ºC (Thermoreactor TR 300 from Merck) for 2 hours, then measuring the absorbance (Spectroquant Nova 60) corresponding to the reduced chromium. The samples with concentrations of chlorides higher than the maximum permissible by the method (2000 mg/L), such as the simulated cotton effluent, were firstly diluted. 3.3.5 Chlorides, Dissolved Phosphorus, Nitrates and Sulfates Chlorides, nitrates, dissolved phosphorus and sulfates were measured by ion chromatography (Dionex DX 120) using a Dionex Ionpac AS9-HC 4 mm (10-32) column and sodium carbonate 9 mM as eluent – Method 4110 B [APHA, 1998]. 3.3.6 Color The color of the samples was quantified by measuring the absorbance at the wavelength of maximum absorbance (520, 600 and 610 nm for synthetic cotton, real cotton and synthetic acrylic effluents, respectively), using a molecular absorption spectrophotometer (Pye Unicam, model He l ios α). As the absorbance of the wastewaters varies with pH, the pH in the treated effluent was adjusted to the initial value, whenever necessary, before absorbance measurement. To evaluate de compliance with the discharge limit as defined in Ordinance No. 423/97 of 25 June, the samples were diluted 40 times and visually checked the presence or absence of color. Part II 79 3.3.7 Conductivity The conductivity at 20 ºC was determined using a conductivity probe (WTW TetraCon 325) and a conductivity meter (WTW LF538) - Method 2510 B [APHA, 1998]. 3.3.8 Dissolved Iron The dissolved iron was determined by the atomic absorption spectrometry-flame method (AAS GBC model 932 AB Plus) - Method 3111 B [APHA, 1998], after filtration of the samples through cellulose nitrate membranes (Albeit) with pore size of 0.45 µ m. 3.3.9 Dissolved Oxygen Carbon The DOC of the samples was obtained, after filtration through nylon filter membranes with pore diameter of 0.45 µm, by catalytic oxidation at 680 ºC using a 5000 A - Shimadzu Total Carbon analyzer, followed by quantification of the CO 2 formed by infra-red spectrometry as described in Method 5310 D [APHA, 1998]. DOC was calculated as the difference between the total dissolved carbon (TDC) and the inorganic carbon (IC) in the liquid sample. 3.3.10 Hydrogen Peroxide The quantification of the hydrogen peroxide was performed as described by Sellers [1980]. The method is based on the measurement of the intensity of the yellow-orange color resulting from the reaction of hydrogen peroxide with titanium oxalate. The samples were previously filtered through nylon filter membranes with pore diameter of 0.45 µm. 3.3.11 Inhibition of Vibrio Fischeri The inhibition test of bacterium Vibrio fischeri was performed according to the standard DIN/EN/ISO 11348-3 [International Organization for Standardization, 2005]. The samples Chapter 3 – Materials and Methods 80 were added to V. fisheri culture medium at 15 ºC and the bioluminescence was measured after 5, 15 and 30 minutes in a Microtox Model 500 analyzer. The samples were first neutralized to pH ~ 7 with HCl or NaOH 1N. 3.3.12 pH The pH was measured with a combined electrode (Hanna Instruments HI 1230) connected to a pH-meter (Hanna Instruments HI 8424)- Method 4500 H + B [APHA, 1998]. 3.3.13 Total Nitrogen Total nitrogen was quantified by potassium persulfate digestion (Method 4500 N. C [APHA, 1998]), which converts organic nitrogen, ammonia and nitrite into nitrate, with subsequent determination of nitrate by molecular absorption spectrophotometry after reaction with brucine (Method D992-71 of ASTM [1973]). 3.3.14 Total Phosphorus The total phosphorus was quantified by measuring the intensity of blue color resulting from the reaction of orthophosphate with ascorbic acid, after acid digestion with ammonium persulfate to convert all phosphorus into orthophosphate (Method 4500 P. E [APHA, 1998]). 3.3.15 Total Suspended Solids and Volatile Suspended Solids Total suspended solids (TSS) and volatile suspended solids (VSS) were evaluated by gravimetry - Method 2540 B and Method 2540 E [APHA, 1998], respectively. Part II 81 3.3.16 HPLC Analyses For the high performance liquid chromatography (HPLC) analyses (in a VWR chromatograph, Elite Lachrom model) of the intermediates formed during oxidation, a Purospher Star RP-18 (5 µm) column was used, at a temperature of 30 ºC, with a mixture of acetonitrile (A) and water (W) as eluent, flow rate of 1 mL/min in gradient mode (at t=0 min, 30% of A and 70% of W, t=20 min, 63% of A and 37% of W, t=22 min, 63% of A and 37% of W, t=23 min, 30% of A and 70% of W and t=30 min, 30% of A and 70% of W). The peak amplitude was measured with a diode array detector (DAD) (at 254 nm for acrylic effluent and 200 nm for polyester effluent). 3.3.17 Zahn-Wellens Test The Zahn–Wellens test was performed according to method 302B of OECD [1992]. A volume of 250 mL of wastewater was added to an open glass vessel, magnetically stirred (Velp Scientifica model Multi15 Stirrer) and kept in the dark inside a thermostatic refrigerator (PSelecta model HOTCOLD - M) at 25 ºC. Then 0.25 g of activated sludge from the aeration tank of a WWTP treating textile effluents (Rabada, Santo Tirso), previously centrifuged, and mineral nutrients (KH 2 PO 4 , K 2 HPO 4 , Na 2 HPO 4 , NH 4 Cl, CaCl 2 , MgSO 4 and FeCl 3 ) were added to the samples. The control and blank experiments were prepared substituting the effluent by lauryl sulfonate (0.2 g/L) and distilled water, respectively. The percentage of biodegradation (D t ) was determined by Equation 3.1: (3.1) 100 * C - C C - C - 1 D BAA Bt t       = where C A and C BA are the DOC concentrations (mg/L) of the mixture and blank, measured 3 h after the beginning of the experiment, C t and C B are the DOC (mg/L) of the mixture and blank, measured at the sampling time t. Chapter 3 – Materials and Methods 82 3.4 Experimental Procedure 3.4.1 Coagulation/Flocculation The coagulation/flocculation experiments were carried out in a Jar-test apparatus (Isco) (Figure 3.6). A volume of 300-500 mL of effluent was used and the pH adjusted using NaOH (1 or 10 N) or H 2 SO 4 (1 N), depending on the pH required for the coagulation stage and on the effluent natural pH. A high stirring speed (which was varied in the parametric studies in the range 100-200 rpm, corresponding to a velocity gradient, G, between 237 and 669 s -1 ) was then promoted and the coagulant (FeSO 4 .7H 2 O – Merck, 99% of purity – or Fe 3 (SO 4 ) 2 – Rieden Häen, 99% of purity) added. Immediately after this, the pH was readjusted (if necessary) and the agitation was prolonged for the intended time (t coagulation ). After the coagulation, the flocculant was added just before the beginning of the slow stirring stage (20-50 rpm, corresponding to a velocity gradient between 21 and 84 s -1 ). This stage proceeded for a given time (t flocculation = 15-45 minutes) in order to facilitate the flocs aggregation for an easier sedimentation. The experiments were performed at controlled temperature by placing the Jar-test apparatus (VELP P4) inside a thermostatized chamber (Velp Scientifica FOC 225E), the addition of the coagulant being done only after temperature stabilization. Figure 3.6 – Diagram of the Jar-test set-up. Part II 83 3.4.2 Fenton´s Reaction Fenton’s oxidation was carried out in an 1 L-capacity jacketed batch reactor connected to a thermostatic bath (Grant Y6) for water circulation (Figure 3.7), in order to maintain the temperature inside the reactor at the desired value. Figure 3.7 – Diagram of the Fenton’s oxidation set-up. In all runs, 500 mL of raw wastewater or pre-treated effluent was loaded into the reactor and after temperature stabilization, the pH was adjusted to a predefined value with 1 N H 2 SO 4 or 1 or 10 N NaOH. When required, ferrous sulfate heptahydrate was added and the reaction started with the addition of H 2 O 2 , 30% (w/v). All reagents were from Merck, analytical grade. The oxidation reaction proceeded under constant stirring, using a magnetic bar and a stir plate (Falc). Periodically, samples were taken from the reactor and the reaction stopped in the flasks by the addition of large excess sodium sulfite (that reacts instantaneously with remaining hydrogen peroxide) for measuring the dissolved organic carbon (DOC) as described above. As regards other parameters, namely chemical oxygen demand (COD), biochemical oxygen demand after 5 days (BOD 5 ), pH, color, specific oxygen uptake rate (SOUR or k’) and toxicity (inhibition of Vibrio fischeri), the reaction was stopped by eliminating the residual H 2 O 2 and by precipitation of the iron catalyst. For that, the pH of the final effluent was raised to 12.3 by addition of 10 N NaOH, the sample was heated at 80 °C for 10 minutes and finally neutralized (to pH ~7.0) with conc. H 2 SO 4 . The samples for toxicity assessment were neutralized with HCl 1N, instead of H 2 SO 4 , as proposed by Chapter 3 – Materials and Methods 84 the analytical methodology. In this case sodium sulfite was not used because it leads to deactivation of V. fischeri and consequently to a decay in the luminescence. The supernatant resulting from the Fenton´s oxidation was acidified to pH 1 with conc. HNO 3 to ensure that the iron was kept dissolved for the subsequent stage of coagulation/flocculation. The analyses of the effluent were performed immediatley. 3.4.3 Photo-Fenton Oxidation 3.4.3.1 Photo-Fenton with Artificial Radiation The tests took place in a closed cylindrical reactor of 1-liter capacity, which was loaded with 800 ml of effluent to be treated. The reactor was equipped with a UV/visible lamp (150 W high pressure mercury vapor - Heraeus TQ 150, corresponding to 500 W/m 2 - which emits UV/visible radiation at wavelengths from 200 to ~600 nm), located axially inside a dip immersion quartz tube (cf. Figure 3.8). The jacketed quartz tube was connected to a thermostatic bath (GRANT Y6) for temperature control through water recirculation. The reactor was also provided with a magnetic stir plate (Falc). Figure 3.8 – Diagram of the photo-Fenton set-up with mercury lamp TQ 150. Part II 85 In runs using artificial radiation, the reactor was loaded with 800 ml of effluent to be treated. After the effluent reached the desired temperature, the pH was adjusted to the estabilished value with 1N H 2 SO 4 . In the case of direct photolysis experiments, the lamp was then connected, and samples collected at pre-established periods to measure the absorbance and dissolved organic carbon (DOC). In runs where one intended to combine UV/Vis radiation with H 2 O 2 (30% w/v from Merck), the mercury lamp was switched on at the same time that the reagent (H 2 O 2 ) was added. In this case, before analyzing the samples, the remaining hydrogen peroxide was removed by the addition of large excess of sodium sulfite (six times the stoichiometric value corresponding to the amount of hydrogen peroxide added at the beginning of the test). In photo-Fenton experiments, the adopted procedure was basically the same, with one intermediate step for adding ferrous sulfate heptahydrate (Merck) before turning on the lamp and adding hydrogen peroxide. Again, hydrogen peroxide was eliminated from the samples taken throughout the reaction by adding sodium sulfite, before DOC and the absorbance measurement. In the samples collected after 60 minutes of reaction for the subsequent determination of COD and BOD 5 , the reaction was stopped by raising the pH to 12.3 with the addition of 10 M NaOH (from Merck), heating the samples at 80 °C for 10 minutes and neutralizing with concentrated H 2 SO 4 until pH ~ 7.0; this procedure was adopted because sodium sulfite interferes with those analytical determinations. In photo-Fenton tests the light flux that reached the wastewater was varied by circulating, in the jacket of the quartz tube, a solution of dye Solophenyl Green BLE 155% at different concentrations, as described by Silva and Faria [2009]. These concentrations have been previously determined by potassium ferrioxalate actinometry [Kuhn et al., 2004]. Figure 3.9 shows the variation of the radiation intensity (measured with a Kipp & Zonen B.V., model CUV 5 UV radiometer, and a Delta OHM, model D9221 visible radiometer - placed outside the reactor and at mid-height of the dip immersion quartz tube) that reaches the solution to be treated as a function of the dye concentration in the solution circulating in the jacket. Chapter 3 – Materials and Methods 86 Figure 3.9 - Variation of the radiation intensity with the Solophenyl Green BLE 155% concentration circulating in the photo-reactor jacket. 3.4.3.2 Photo-Fenton using Simulated Solar Radiation The photoreactor using simulated solar radiation actually comprises two reactors (Figure 3.10): i) an 1-liter capacity closed cylindrical reactor equipped with a jacket for water recirculation from a thermostatic bath (RW-0525G the Lab Companion) for temperature control and ii) a tubular reactor (volume of ~ 0.78 L, 100% volume irradiated) placed inside the Solarbox (ATLAS, model SUNTEST XLS+). The Solarbox has a Xenon lamp of 1700 W that emits radiation at wavelengths from 300 to 800 nm. In runs with simulated solar radiation the cylindrical reactor was fed with 800 mL of effluent and the pH adjusted to the predefined value with 1 N H 2 SO 4 . The solution was continuously pumped to the tubular reactor and recirculated back into the cylindrical one (with the aid of a peristaltic pump - Ecoline VC-380 II Ismatec), at a flow rate of 0.65 L/min (~ 0.12 min residence time in the tubular reactor). After reaching the desired temperature, heptahydrated ferrous sulfate (Merck) and hydrogen peroxide (30% w/v – Merck) were added to the cylindrical reactor. Then the lamp was switched on. During the reaction the cylindrical reactor contents were stirred by a magnetic bar and stir plate (Velp Scientifica, model ARE). Samples were taken at pre-defined times and the reaction was stopped as described in the previous section for dark Fenton experiments. The radiation intensity in the range 300 0 100 200 300 400 500 0 100 200 300 400 500 Intensity (W/m2) ) ) ) [Dye] (mg/L) Part II 87 - 400 nm was measured in the tubular reactor by an UV radiometer (Kipp & Zonen B.V., model CUV 5). Figure 3.10 – Diagram of the sun-test set-up. 3.4.4 Biological Oxidation in Sequencing Batch Reactor The SBR is a jacketed cylinder (20 cm internal diameter, 45 cm total height and 30º slope conical bottom; effective working volume = 5.0 L) connected to a thermostatic bath (Isco GTR 90, from Italy). Figure 3.11 shows the installation set-up. The biological reactor was operated at constant temperature (25 °C) during 12 hours per cycle (1 h feeding, 6 h reaction, 4 h sedimentation, 0.8 h discharge and 0.2 h idle), up to 10 cycles (i.e., when the parameters analysed in the treated effluent and described below showed nearly contant values from cycle to cyle – pseudo steady-state conditions). In the first cycle the reactor was fed with 2.5 L of wastewater with pH previously adjusted to ~7.0 using 1M H 2 SO 4 and 10 M NaOH, after adding phosphorus (as phosphate buffer) or nitrogen (as urea) whenever necessary to ensure the minimum quantity required for biological treatment Part III 95 4 Coagulation/Flocculation with Fe 2+ as Coagulant 4.1 Introduction The present chapter focuses on determining the best operating conditions for the coagulation/flocculation process using iron (II) as coagulant to treat different types of synthetic textile wastewaters simulating cotton, acrylic and polyester dyeing. It is evaluated the effect of stirring speed, contact time, temperature, pH and doses of coagulant (ferrous sulphate) and flocculants (Magnafloc 155 or Superfloc C-573) in color and dissolved organic carbon (DOC) removal from the wastewaters. The selected flocculants are commonly employed in the treatment of textile dyeing wastewaters. However, the use of an iron salt as coagulant is related to the possibility of integrating the coagulation/flocculation process with a subsequent Fenton-like oxidation treatment in which the soluble remaining iron is used as catalyst, thus decreasing the overall consumption of chemicals. The use of the soluble iron resulting from the coagulation/flocculation in the partial mineralization of organic compounds by such oxidation treatment is addressed in chapters 6-8. 4.2 Materials and Methods 4.2.1 Preparation of Simulated Textile Wastewaters The simulated effluents were prepared as described in section 3.2 of chapter 3 and the main characteristics of the synthetic effluents are reported in Table 3.4 (cf. section 3.2.1). 4.2.2 Coagulation/Flocculation Experiments The experimental procedure concerning the coagulation/flocculation experiments was described in section 3.4.1 – Materials and Methods. The effluent pre-treated by coagulation employing the optimal conditions was then subjected to flocculation experiments. Magnafloc, an anionic polyacrylamide (molecular weight around 5×10 6 , density ~750 kg/m 3 , incolor solid) and Superfloc C-573, a cationic Chapter 4 – Coagulation/Flocculation with Fe 2+ as Coagulant 96 polyamine (molecular weight around 10 4 , density 1.14-1.18 kg/m 3 , yellow liquid), were tested as flocculants, since they have been considered as suitable polymers to treat this kind of wastewaters. The samples of supernatant were collected after 30 minutes of sedimentation and the dissolved organic carbon (DOC) determined immediately (despite DOC values in the supernatant of the same samples analysed after 24 h of sedimentation were identical to those obtained after 30 minutes). The absorbance was, however, read after one day of sedimentation to minimize the number of very small particles of iron hydroxide in suspension. Moreover, the supernatant sample for color measurement was centrifuged (Mini Spin Eppendorf) at 13400 rpm for 2 minutes. 4.2.3 Analytical Methods The experimental methods used in this study were already mentioned in section 3.3 of Chapter 3. The parameters were measured in duplicate and the variation coefficients were less than 2% for DOC, < 1% for absorbance, < 9% for BOD 5 and < 3% for the other parameters. 4.3 Results and Discussion In this chapter are reported experiments carried out to determine the effect of stirring rate and time on the color and DOC removal during the coagulation process. However, these variables were not very effective, as shown below from the results obtained for the polyester and cotton effluents. Further, the effect of other more relevant operating conditions as temperature, pH and ferrous salt concentration on the color and DOC removal efficiency was analyzed for the three effluents. The same approach was adopted for the flocculation stage after being submitted to coagulation at the optimal conditions. Thus, the influence of stirring speed and time is discussed for two effluents, but other more significant variables (flocculant type and concentration) are analyzed in further detail for all effluents. Part III 97 4.3.1 Effect of Stirring Speed and Time on the Coagulation Stage The stirring rate in the coagulation stage should be high and according to previous workers values around 100 rpm were proposed [Satterfield, 2004; Bose, 2010; Poland and Pagano, 2010]. Thus, experiments were performed changing this variable in the range 100 - 200 rpm (G between 237 and 669 s -1 ) for cotton and polyester effluents. Values from 1 minute to 3 minutes [Eckenfelder, 2000; Bose, 2010; Poland and Pagano, 2010] have been proposed for the duration of this initial stage. To study the effect of this variable, the stirring time (t coagulation ) was varied between 1 to 5 minutes. It was found that both variables do not affect the color or the DOC removal for both effluents (cf. Appendix - Figures. A1 and A2). DOC removals were ~27% and ~30% for the polyester and cotton effluents, respectively. Around 74% of color removal was obtained for the cotton effluent whatever the stirring rate and time (the polyester is colorless). These results allow concluding that these variables, stirring rate and time, do not play an important role in the coagulation stage. 4.3.2 Effect of the Temperature on the Coagulation Stage In this study the effect of temperature in the coagulation process was analyzed; although it has not been commonly investigated in the open literature, Edeline [1992] reported the temperature as being a variable to take into account. Thus, the temperature was varied between 15 and 50 ºC while the previous variables were fixed at v coagulation = 150 rpm (G = 435 s -1 ) and t coagulation = 3 min. Figure 4.1 shows that for the polyester wastewater, the DOC removal is almost independent of temperature, remaining nearly constant (~27%) in the studied range; the same applies with the cotton effluent. In the acrylic wastewater a slight increase is noticed in the temperature range from 15 to 22 ºC, then remaining nearly constant. Removal of organic carbon is higher in the cotton and lower in the acrylic compared to the polyester effluent. The effect of temperature on color removal is much more marked, increasing from 11.4% and 4.7% at 15 ºC up to ~74% and ~32% at 22 ºC for cotton and acrylic wastewaters, respectively, but performance is no further improved at 50 ºC (Figure 4.1 b). Thus, subsequent runs were performed at room temperature. The increased performance with temperature may be a consequence of the improved kinetics as occurs in most Chapter 4 – Coagulation/Flocculation with Fe 2+ as Coagulant 98 chemical reactions (Arrhenius dependency). The effect of temperature on coagulation has been analyzed by Duan and Gregory [2003], indicating that at lower temperatures the coagulation with hydrolyzing metals is less efficient. Temperature effects may be due to physical or chemical factors, where physically the temperature affects the viscosity and consequently the transport or collision rates. On the other hand, the chemical influence is on the level of hydrolysis reactions, precipitation and solubility of the metal hydroxide. Figure 4.1 – Variation of DOC (a) and color (b) removals with temperature in the coagulation stage for the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, [Fe 2+ ]=200 mg/L and pH=8.3). 4.3.3 Effect of the pH on the Coagulation Stage One of the most important variables in the coagulation process using inorganic salts is the pH. This occurs because the coagulant (iron salt in this case) is converted into different ionic species as the pH value changes thus, influencing the coagulation. In alkaline pH, depending on the redox potential, some iron (II) precipitates as a hydroxide (green rust) capable of absorbing anions because of the presence of positive electrical charges on its surface. However, for pH<10 the predominant iron species are Fe 2+ (practically the only species for pH<7) and Fe(OH) + . In this work, the pH was changed in the range from 3.5 to 10.4 but in the acrylic effluent experiments a pH above 8.3 was not used because a change of the blue color to light grey was observed. Figure 4.2 shows that there are optimum pH values for the DOC and color removal which changes from one effluent to another. In general, the optimum pH value is the same for 0 10 20 30 40 50 60 15 22 50 DOC removal (%) T(ºC) Acrylic Polyester Cotton a) 0 20 40 60 80 100 15 22 50 Color removal (%) T (ºC) Acrylic Cotton b) Part III 99 either DOC or color removal for each wastewater used. It can be summarized that for the polyester effluent there is no DOC removal at all at pH 3.5 or 5, but an optimum exists at pH 8.3 (27.6% removal). For the cotton effluent, a pH of ca. 9.4 led to the greatest DOC and color removals (40.3% and 90.1%, respectively). As for the acrylic effluent, the DOC removal at a pH of 3.5 and 5 was low and the higher removals were observed at a pH of 7.2 (~10% for DOC and 55.3% for color). It is worth mentioning that the optimal pH follow the order of the effluent's natural pH values; acrylic < polyester < cotton (cf. Table 3.4 in section 3.2.1.3). Figure 4.2 – Influence of pH on DOC (a) and color (b) removals by coagulation applied to the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, [Fe 2+ ]=200 mg/L and T =T ambient =22-23 ºC). The optimum pH values obtained, which will be adopted in the subsequent runs, are close to the values commonly appointed in others studies with the same coagulant for textile effluents, but the optimum pH depends strongly on the nature of the wastewater to be treated. For example, pH values of 5.0 and 6.0 have been reported for white and red wine effluents, respectively [Braz et al., 2010], 7.4 for mechanical pulping effluent coagulation [Stephenson and Duff, 1996], around 8.0 for dairy wastewater [Kushwaha et al., 2010] and cosmetic manufacturing wastewater [Perdigón-Melón et al., 2010], 8.5 for purified teraphthalic acid wastewater [Verma et al., 2010] and 9.4 for effluent from personnel care products manufacturing [El-Gohary et al., 2010] . Other authors fixed the pH at 9.0 [Golob et al., 2005] or 9.5 [Selcuk, 2005] for dye containing wastewaters. 0 10 20 30 40 50 60 3.5 5 7.2 8.3 9.4 10.4 DOC removal (%) pH Acrylic Polyester Cotton a) 0 20 40 60 80 100 3.5 5 7.2 8.3 9.4 10.4 Color removal (%) pH Acrylic Cotton b) Chapter 4 – Coagulation/Flocculation with Fe 2+ as Coagulant 100 4.3.4 Effect of the Coagulant (Fe 2+ ) Concentration The dose of coagulant necessary for the treatment of effluents by coagulation, and particularly those from textile industries, depends on the characteristics of the wastewaters [Eckenfelder, 2000]. Therefore, it is necessary to evaluate the effect of the coagulant dose (Fe 2+ ), which was herein changed in the range of 15 to 1000 mg/L for polyester and cotton effluents and from 200 to 4000 mg/L for acrylic ones. These ranges were enough to find optimum doses, and the others variables that influence the process were fixed at the optimum values obtained before. The results of DOC removal (Figure 4.3 a) permitted concluding that for cotton wastewaters, the optimum Fe 2+ dose is 200 mg/L and higher doses are also not required for reducing the color of such effluents (Figure 4.3 b). For the acrylic, the optimum is shifted towards a much higher coagulant dose; 3000 mg/L for DOC removal while for the color removal it increased up to 500 mg/L and then remained almost unchanged. The higher concentration of Fe 2+ required is probably a consequence of the higher load of organic matter in this effluent (Table 3.4 in section 3.2.1.3). For the polyester, Figure 4.3 a shows that the DOC removal increases with the Fe 2+ concentration up to a dosage of 200 mg/L, and that for higher doses the efficiency remains nearly constant. The optimum dose of Fe 2+ in this case is quite similar to that observed with the cotton effluent, which might be related to the similar organic carbon content of both wastewaters (Table 3.4 of section 3.2.1.3). In the selected conditions, around 90% of color removal was reached for cotton and 65.8% for acrylic, while efficiencies of 40.3%, 17.7% and 27.6% were obtained for DOC removal in cotton, acrylic and polyester effluents, respectively. Other studies report the occurrence of an optimal in coagulant dose for treat wastewaters by chemical coagulation/flocculation [Amokrane et al., 1997 Tatsi et al., 2003]. Part III 101 Figure 4.3 – Variation of DOC (a) and color (b) removals with the concentration of coagulant (Fe 2+ ) for the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =23-25 ºC and pH polyester =8.3, pH cotton =9.4 and pH acrylic =7.2). Georgious et al. [2003] achieved the best results for color and COD elimination from cotton dyeing wastewater using a combination of lime (800 mg/L) and FeSO 4 .7H 2 O (1000 mg/L). On the other hand, Golob et al. [2005] achieved almost full decolourization of dyebath effluents (cotton/poliamide blends) using 20 mg/L of FeSO 4 .7H 2 O but TOC was only reduced by 25%. In spite of using a ferric salt, Joo et al. [2007] concluded that 3000 mg/L was the required dose for maximizing the color removal and 4000 mg/L for maximizing the COD removal of a reactive dye synthetic wastewater. These and other published data show that the coagulant dose is highly variable, depending on the wastewater characteristics, dye concentration and overall organic content, in agreement with our findings. Additionally, it must be emphasized that excess of coagulant can promote the undesirable stabilization of colloids, which has been observed in different studies [Aziz et al., 2007; Liang et al., 2009]. In the present study, for the acrylic dyeing wastewater, a dose around 500 mg/L should be adequate to maximize the color removal but it was increased to maximize DOC removal (in spite of not exceeding 17.7% without flocculant addition). Of course, for practical purposes other criteria should be also taken into account, namely the extra cost of the coagulant dose, and balanced with the benefit in terms of process performance. 0 10 20 30 40 50 60 15 50 100 200 500 1000200030004000 DOC removal (%) [Fe 2+ ] (mg/L) Acrylic Polyester Cotton a) 0 20 40 60 80 100 15 50 100 200 500 1000200030004000 Color removal (%) [Fe 2+ ] (mg/L) Acrylic Cotton b) Chapter 4 – Coagulation/Flocculation with Fe 2+ as Coagulant 102 4.3.5 Influence of the Stirring Speed and Time in the Flocculation Stage Usually the stirring speed in the flocculation stage varies in the range 25-35 rpm [Bose, 2010; Poland and Pagano, 2010] and lasts between 12 and 35 min [Phipps & Bird, 1995; Lafleur, 1997; Eckenfelder, 2000; Bose, 2010; Poland and Pagano, 2010]. For evaluating the effect of stirring speed on the flocculation, this parameter (v flocculation ) was varied in the range 20-50 rpm, i.e., G between 21 and 84 s -1 (at a fixed time of 15 min and a Magnafloc 155 concentration of 2.5 mg/L). Then, further experiments were performed while changing the flocculation time from 15 to 45 min. With these experiments it was concluded that v flocculation and t flocculation do not have any appreciable influence on either color or DOC removal (cf. Figures A.3 and A.4 in Appendix). Therefore, in subsequent experiments these variables were fixed at 20 rpm (G = 39 s -1 ) and 15 min, respectively. 4.3.6 Influence of the Flocculant Type and Dosage Small dosages of a polyelectrolyte (0.5-3 mg/L and 1-5 mg/L) permit the formation of large flocks and accelerate sedimentation [Grau, 1991; Poland and Pagano, 2010]. Two series of experiments were then performed for each synthetic effluent using two flocculants: Magnafloc 155 (dose in the range 0.25 - 5 mg/L) and Superfloc C-573 (from 0.25 to 5 mg/L for cotton and polyester effluents and from 0.1 to 5 mg/L for the acrylic one) in order to study the influence of the flocculant type and dosage on the flocculation stage. Figure 4.4 shows that the optimum doses of Magnafloc 155 are as follows: ca. 1 mg/L for polyester and 0.5 mg/L for both cotton and acrylic effluents. The overall DOC removals using the optimum doses were 33.3, 45.4 and 21.4% for polyester, cotton and acrylic effluents, respectively, while color removals were of 91.4% and 78.9%, respectively for cotton and acrylic effluents. Part III 103 Figure 4.4 - Variation of DOC (a) and color (b) removals with the dose of flocculant (Magnafloc 155) for the different simulated effluents (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =23-25 ºC, pH polyester =8.3, pH cotton =9.4, pH acrylic =7.2, [Fe 2+ ] polyester =[Fe 2+ ] cotton =200 mg/L, [Fe 2+ ] acrylic =3000 mg/L, v flocculation =20 rpm and t flocculation =15 min). Doses of Superfloc C-573 for maximum DOC removals were 0.5 mg/L for cotton and polyester effluents and 0.25 mg/L for the acrylic one, these doses leading to DOC removals of 43.2%, 32.0%, and 28.3%, respectively (Figure 4.5 a). Moreover, Figure 4.5 b shows that color removal in cotton wastewater (~90%) is almost independent of the flocculant dose, but for the acrylic effluent the best overall efficiency for color reduction (93.8%) was obtained using a Superfloc dose of 0.25 mg/L. Similar doses were determined by other authors for dyes containing wastewaters, although different flocculants were used [Bes-Piá et al., 2002; Joo et al., 2007; El-Gohary and Tawfik, 2009]. 0 10 20 30 40 50 60 0 0.25 0.5 1.0 2.5 4.0 5.0 DOC removal (%) [Magnafloc 155] (mg/L) Acrylic Polyester Cotton a) 0 20 40 60 80 100 0 0.25 0.5 1.0 2.5 4.0 5.0 Color removal (%) [Magnafloc 155] (mg/L) Acrylic Cotton b) * This Chapter is based on the publication “Rodrigues C.S.D.; Madeira, L.M.; Boaventura, R.A.R. Synthetic Textile Wastewaters Treatment Using Ferric Salt as Coagulant”. Submitted to Environmental Engineering and Management Journal. Chapter 5 Coagulation/Flocculation with Fe 3+ as Coagulant * Part III 113 5 Coagulation/Flocculation with Fe 3+ as Coagulant 5.1 Introduction The combination of coagulation/flocculation and Fenton oxidation processes has been already applied to wastewaters from the textile industry [Kang et al., 2002; Wang et al., 2008] and other effluents [Martins et al., 2005]. However, when using iron salts as coagulants, the residual soluble iron contributes to a reduction in the operating costs associated with Fenton’s oxidation, often used downstream from coagulation/flocculation, wherein the residual iron is used as catalyst. The purpose of this chapter is to assess the applicability of ferric sulphate as coagulant in combination with an anionic (Magnafloc 155) or cationic (Superfloc C-573) flocculant for the removal of organic matter and color from polyester, cotton and acrylic dyeing synthetic wastewaters. In spite of the recommendations of the manufacturers (Allied Colloids and American Cyanamid Co., respectively), Magnafloc 155 and Superfloc C-573 have not been used so far for textile dyeing wastewater treatment. Optimized conditions for key variables as pH, Fe 3+ and flocculant doses were also determined. This work is the continuation of a previous one (chapter 4) where ferrous sulphate was used as coagulant and therefore it allows comparing the performances of Fe(II) and Fe(III) salts for each synthetic effluent, thus aiming to infer if the same salt could be beneficially used in all cases or not. The main objective of both studies was to take advantage of the dissolved iron present in the effluent resulting from the coagulation process in a downstream ironcatalysed oxidation – the well-known Fenton´s advanced oxidation process, addressed in subsequent chapters. This additional treatment, alone or supplemented by a biological process, is justified by the limited capability of coagulation/flocculation for producing per se an effluent that meets the discharge limits (for pH, COD, BOD 5 and color) imposed by the Portuguese legislation (Ordinance No. 423 of June 25, 1997, for discharge of textile wastewaters). Chapter 5 – Coagulation/Flocculation with Fe 3+ as Coagulant 114 5.2 Materials and Methods 5.2.1 Preparation of Simulated Textile Effluents The simulated effluents used in the work reported in this chapter were prepared as described in section 3.2.1 of chapter 3. 5.2.2 Coagulation/Flocculation Experiments Iron sulfate (Fe 2 (SO 4 ) 3 ; CAS: 10028-22-5) used as coagulant was supplied by Quimitécnica S.A. (Portugal) as a brown solution with pH = 2.0±0.5 and specific gravity = 1.56 ± 0.2 at 20 ºC. The working solution was prepared by diluting the commercial product with distilled water to obtain a solution with 50 g Fe 3+ /L. Magnafloc 155 is an anionic polyacrylamide (molecular weight around 5×10 6 , density ~750 kg/m 3 , whitish-yellow solid) from Allied Colloids (England) and Superfloc C-573 is a cationic polyamine (molecular weight around 10 4 , density 1.14-1.18 kg/m 3 , yellow liquid) from American Cyanamid Co (USA), both used as flocculants in this work. The optimum pH as well as the optimal coagulant and flocculant doses were determined from experiments performed in a Jar-test apparatus according to the description given in section 3.4.1. For either DOC or color analyses the supernatant was previously centrifuged (Mini Spin Eppendorf, Germany) at 13400 rpm for 2 minutes. 5.2.3 Analytical Methods The analytical procedures were performed as described in section 3.3 of chapter 3. Part III 115 5.3 Results and Discussion In a previous work (chapter 4) it was found that some operating conditions, namely the stirring speed and stirring time during the coagulation stage, have almost no effect on either color or DOC reduction from synthetic textile dyeing effluents. So, those parameters were kept constant at 150 rpm and 3 min, respectively, while determining the effect of both pH and Fe 3+ concentration on color and organic matter removal in the coagulation stage. The responses selected in this parametric study were color and DOC reduction because they are faster to assess; besides, they are closely related to legislated parameters (pH, COD, BOD 5 and color), which are nevertheless assessed after optimizing process conditions to see if the final effluent meets legislated standards. 5.3.1 Influence of pH As found previously with a Fe 2+ salt (chapter 4), the pH is one of the most important factors to take into account in the coagulation process. In this work, where a Fe 3+ salt was used as coagulant, the pH was varied from 3.5 to 10.4 for polyester and cotton effluents. For the acrylic effluent no results are presented for pH > 8.3 because it was observed a change in the colour of the effluent (from blue to light grey). The obtained results concerning the effect of the pH are shown in Figure 5.1. They allow concluding that there are optimal pH values for DOC removal (Figure 5.1 a): 9.4 for the polyester effluent (33.4% of DOC reduction) and 5.0 for the cotton effluent (38.7% of DOC reduction). For the acrylic effluent the removal increased with the pH, but at pH 8.3 only a reduction of 13.6% in DOC was obtained. Regarding color removal (Figure 5.1 b), the optimum occurred at pH = 5.0 (32.0% of color reduction) for the cotton effluent and increased with pH, in the range studied, for the acrylic effluent, with maximum color removal of 41.2% at pH = 8.3. At the optimum conditions, and for the cotton effluent, the coagulation occurs most probably by charge neutralization and inclusion in an amorphous hydroxide precipitate (sweep flocculation), because at pH 5.0 the species present in solution are Fe 3+ ions and hydrolysable species (Fe(OH) 2+ and Fe(OH) 3 ) [Duan and Gregory, 2003]. For the acrylic and polyester effluents, with optimum coagulation pH in the alkaline zone, Fe(OH) 3 and Fe(OH) 4are the main species present in solution (Duan and Gregory, 2003), and one can Chapter 5 – Coagulation/Flocculation with Fe 3+ as Coagulant 116 consider that the coagulation principally occurs by incorporation in iron hydroxide precipitates. Figure 5.1 – Influence of pH in DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, [Fe 3+ ] polyester = [Fe 3+ ] cotton = 200 mg/L, [Fe 3+ ] acrylic = 500 mg/L and T=T ambient = 22-23 ºC). The optimum pH values obtained for the cotton and polyester effluents are within the ranges indicated by Edeline (1992) when using Fe 2 (SO 4 ) 3 as coagulant: 3.5-7 and > 9. The best pH for the acrylic effluent was not determined due to the color change for pH > 8.3, as above mentioned. The optimum pH for the cotton effluent (5.0) is also close to that obtained in other studies with the same coagulant, even applied to different wastewaters. For instance, Joo et al. (2007) pointed out an optimum pH between 4 to 7 for the treatment of textile effluents, while Aziz et al. (2007) and Liang et al. (2009) obtained the maximum efficiency at pH 4 in the treatment of landfill leachate and molasses wastewaters. 5.3.2 Influence of the Fe 3+ Concentration The effect of the coagulant dose was assessed by varying the dosage in the range 15 - 1000 mg/L for polyester and cotton effluents and 200 - 4000 mg/L for the acrylic one. The other variables of the process were fixed at the optimal values determined before, namely the pH. 0 10 20 30 40 50 60 3.5 5.0 7.2 8.3 9.4 10.4 DOC removal (%) pH Acrylic Polyester Cotton a) 0 10 20 30 40 50 60 3.5 5.0 7.2 8.3 9.4 10.4 Color removal (%) pH Acrylic Cotton b) Part III 117 The results obtained (Figure 5.2) show a Fe 3+ optimum dose of 500 mg/L for the polyester wastewater, leading to 35.1% DOC removal. For the cotton effluent both the color and DOC removals increase with [Fe 3+ ] up to 200 mg/L, decreasing for higher concentrations. Maximum removals of 38.7 and 32.0% were achieved for DOC and color, respectively. An optimal concentration of 1000 mg/L was found for the acrylic effluent, yielding 44.7% decolorization and a DOC reduction of only 16.5%. The existence of optimum Fe 3+ doses has been also reported in other studies [Kim et al., 2004; Joo et al., 2007; Anouzla et al., 2009] and has been attributed to the fact that when the coagulant dosage is in excess, the restabilization of colloids can occur [Aziz et al., 2007]. Figure 5.2 – Effect of Fe 3+ concentration on DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, T=T ambient = 23-25 ºC and pH polyester = 9.4, pH cotton = 5.0 and pH acrylic = 8.3). In a previous work using a Fe 2+ salt as coagulant (chapter 4) it was observed that for each textile dyeing effluent the highest reductions both in color and DOC were in general obtained for the same pH and coagulant dose. A similar result was obtained in this study using Fe 3+ . The dose of coagulant necessary for the coagulation process is related to the organic load of the effluent. For the acrylic effluent, with higher organic load (cf. Table 3.4, section 3.2.1.3), a higher dosage of ferric salt is needed. However, the coagulant dose also depends on the global wastewater characteristics, as reported by other authors. For instance, Liang et al. (2009) reported an optimum dose of 3 g/L of ferric sulfate for the treatment of a molasses effluent with a COD of 975±25 mg O 2 /L while Joo et al. (2007) 0 10 20 30 40 50 60 15 50 100 200 500 1000200030004000 DOC removal (%) [Fe3+] Acrylic Polyester Cotton a) 0 20 40 60 80 100 15 50 100 200 500 1000 200 30004000 Color removal (%) [Fe 3+ ] Acrylic Cotton b) Chapter 5 – Coagulation/Flocculation with Fe 3+ as Coagulant 118 obtained the optimum at 4 g/L of ferric salt for the treatment of a textile effluent with a much higher COD load (2968 mg O 2 /L). 5.3.3 Influence of the Flocculant Nature and Dose Some operating conditions, namely the stirring speed and stirring time during the flocculation stage, have almost no effect in either color or DOC reduction for the tested effluents (chapter 4). So, after the coagulation stage, the influence of the nature and concentration of flocculant on color and DOC removal was evaluated, in the flocculation stage, but speed and stirring time were kept constant at 20 rpm and 15 min, respectively. The flocculants (Magnafloc 155 and Superfloc C-573) were employed in concentrations varying between 0.25 to 5 mg/L. The flocculation study was performed using effluents pretreated by coagulation at the best operating conditions previously determined (cf. Table 5.1). Figure 5.3 presents the results obtained using Magnafloc 155. As regards the polyester effluent it can be seen that the DOC removal slightly increases with the flocculant concentration up to 2.5 mg/L (39.9% of DOC removal), but higher doses do not improve the process performance. There is also a very slight increase in DOC reduction for the cotton dyeing wastewater when Magnafloc 155 dose is increased from 0.25 to 0.5 mg/L (41.2%), but then remains nearly constant or is somewhat smaller. Color reduction is nearly independent of the flocculant dose (in the range studied) for this effluent (average reduction ~32.5%). DOC and color removal for the acrylic effluent are low compared to those obtained during the coagulation step, which could be due to the existence of an interaction of the flocculant with the flocs formed during the coagulation and, consequently, the organic compounds and dye are redissolved. It is noteworthy that these runs were repeated several times and the same effect on DOC and color removal was always observed. Part III 119 Figure 5.3 – Effect of Magnafloc155 concentration on DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, T=T ambient = 23-26 ºC, pH polyester = 9.4, pH cotton = 5.0, pH acrylic = 8.3, [Fe 3+ ] polyester = 500 mg/L, [Fe 3+ ] cotton = 200 mg/L, [Fe 3+ ] acrylic = 1000 mg/L, v flocculation = 20 rpm and t flocculation = 15 min). In experiments with Superfloc C-573 (Figure 5.4), the reduction of the DOC (and also color) removal is again observed, as compared to the coagulation step, for the acrylic effluent. DOC removal slightly increases up to 1 mg/L (40.2%) for the polyester dyeing effluent and remains constant for higher doses. A very small increase occurs at 0.5 mg/L (maximum DOC removal of 43.0%) for the cotton effluent. Color removal is again constant in the dose range studied (average ~32.5%). Figure 5.4 – Effect of Superfloc C-573 concentration on DOC (a) and color (b) removal from the different effluents (v coagulation = 150 rpm, t coagulation = 3 min, T = T ambien t = 23-26 ºC, pH polyester = 9.4, pH cotton = 5.0, pH acrylic = 8.3, [Fe 3+ ] polyester = 500 mg/L, [Fe 3+ ] cotton = 200 mg/L, [Fe 3+ ] acrylic = 1000 mg/L, v flocculation = 20 rpm and t flocculation = 15 min). 0 10 20 30 40 50 60 0 0.25 0.5 1.0 2.5 4.0 5.0 DOC removal (%) [Magnafloc 155] (mg/L) Acrylic Polyester Cotton a) 0 20 40 60 80 100 0 0.25 0.5 1.0 2.5 4.0 5.0 Color removal (%) [Magnafloc 155] (mg/L) Acrylic Cotton b) 0 10 20 30 40 50 60 0 0.25 0.5 1.0 2.5 4.0 5.0 DOC removal (%) [Superfloc C-573] (mg/L) Acrylic Polyester Cotton a) 0 20 40 60 80 100 0 0.25 0.5 1.0 2.5 4.0 5.0 Color removal (%) [Superfloc C-573] (mg/L) Acrylic Cotton b) Chapter 9 – Simulated Dyeing Textile Effluents Treatment by the Photo - Fenton Process 222 9.3.1.2.2 Effect of Radiation Intensity In order to minimize the energy costs of the photo-Fenton process, it was decided to analyze the effect of the radiation intensity (between 7 and 500 W/m 2 – corresponding to lamp powers between 2.1 to 150 W) with the doses of reagents tested previously that allowed complying with discharge standards. For example, and according with the data of Table 9.1, for the acrylic effluent the light radiation could be less than 500 W/m 2 for H 2 O 2 doses in the range 6.5-20.0 g/L but not for [H 2 O 2 ] = 2.5-5.0 g/L because in the latter conditions COD of the effluent was above the legislated standard of 250 mgO 2 /L. Figure 9.3 shows the removal of DOC and color for the different radiation intensity tested in the assays with 6.5, 10 and 20 g/L of H 2 O 2 for the effluent resulting from dyeing of acrylic fibers. It can be seen that in all tests the color removal is very fast, requiring only 15 minutes of radiation to reach nearly complete descolorization, and is almost independent of the radiation flux reaching the solution. Regarding the removal of DOC, it can be seen that, in general, and whatever the radiation flux and peroxide dose, it is very fast in the first 15 minutes, then slightly decreases till 60 minutes of reaction, after which DOC remains approximately constant. However, the removal of organic compounds increases with increasing radiation intensity for all hydrogen peroxide concentrations, in agreement with other studies [Kang et al., 2000; Muruganandhan and Swaninanthan, 2004; Modirshahla et al., 2007]. For the maximum radiation used of 500 W/m 2 73, 83 and 96.7% of DOC removal was reached for H 2 O 2 doses of 6.5, 10 and 20 g/L, respectively. Similar experiments were performed for the other effluents, and the conclusions reached are quite similar, of course with different performances. Results obtained are shown in Figures A.5 and A.6 of the Appendix for the cotton and polyester wastewaters, respectively. Part III 223 a) b) c) Figure 9.3 – Effect of radiation intensity on DOC and color removal of the acrylic effluent during the photo-Fenton process for different dosages of hydrogen peroxide: 6.5 g/L (a), 10.0 g/L (b) or 20.0 g/L (c) (T=50 ºC, Fe 2+ :H 2 O 2 =1:57 and pH=3.5). 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 253 W/m2 500 W/m2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 7 W/m2 107 W/m2 220 W/m2 253 W/m2 500 W/m2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 7 W/m2 107 W/m2 253 W/m2 500 W/m2 Chapter 9 – Simulated Dyeing Textile Effluents Treatment by the Photo - Fenton Process 224 Again, in all assays performed in this section the final effluent was characterized in terms of legislated parameters. As illustrated in Table 9.1, in all tests the color was not visible in the effluents after the required dilution. Besides, for every effluent and oxidant dose, it is noticed that the lower the radiation intensity, the lower are the performances reached in terms of COD removal, so that final values of this parameter after 60 min of irradiation are higher; for BOD 5 this not always observed (the small variations observed in this parameter are associated with uncertainties in its determination), but the values reached are always below the legislated standard of 100 mgO 2 /L. This means that for each dose of hydrogen peroxide, for a given type of effluent, there is aa radiation intensity threshold bellow which effluent’s characteristics do not comply with legislated standards. For instance, and taking into the account the values tested, for the acrylic one these values are 500 W/m 2 for [H 2 O 2 ] = 6.5 g/L, 220 W/m 2 for [H 2 O 2 ] = 10.0 g/L and 7 W/m 2 for [H 2 O 2 ] = 20.0 g/L. Of course, the higher the oxidant concentration, the lower is the radiation intensity required to reach COD values below 250 mgO 2 /L. The question remaining is which set of values is more advantageous for industrial implementation; the answer can be given by comparing associated costs, as detailed in the following section. 9.3.1.3 Operating Costs The overall costs of the treatment process are represented by the sum of the capital, operating and maintenance costs. For a full-scale system these costs depend on the flow rate of the effluent, the nature of wastewater, as well as the configuration of the reactors, among other issues. In this study we considered only the costs with the chemicals, i.e., the costs of reagents, and the costs of energy. The first were obtained from Quimitécnica S.A., the average values considered being as follows: H 2 O 2 (49.5% w/v, density at 25 ºC = 1.2 g/cm 3 ) - 365 €/ton; FeSO 4 .7H 2 O (93 % of purity) – 233.7 €/ton, while the latter is about 0.10 €/(kWh). The prices of acid (H 2 SO 4 ) and base (NaOH) were not considered, because the quantities consumed are insignificant. The operating cost was calculated by the sum of costs of hydrogen peroxide, ferrous sulfate and energy consumption, as shown by Equation 9.1. The partial costs were calculated according to Equations. 9.2 - 9.4. Part III 225 Operating Cost = Cost H 2 O 2 + Cost F e 2 + + Cost energy ( 9 . 1 ) Cost H 2 O 2 =Price H 2 O 2 ൬ € ton൰ሾH 2 O 2 ሿ∗ 10 −3 ቀton m 3 ቁ ∗ ρ H 2 O 2 (kg L) % H 2 O 2 100 (kg L) (9.2) Cost Fe 2+ =Price FeSO 4 .7H 2 O ൬ € ton൰ሾFe 2+ ሿ∗ 10 −6 ቀton m 3 ቁ ∗ MM FeSO 4 .7H 2 O MM Fe 2+ % of purity 100 ( 9.3 ) Cost energy = Power of lamp∗ 10 −3 (kW)∗ Price energy ൬ € kWh൰ ∗ time reaction (h) Volume treated effluent ( m 3 ) ( 9 . 4 ) Figure 9.4 shows the effect of hydrogen peroxide dose and the radiation intensity in the total operating costs for treating the acrylic (a), cotton (b) and polyester (c) effluents; in each case, the H 2 O 2 :Fe 2+ ratio was kept constant, so that changing the oxidant dose implies also a change in the catalyst concentration. As expected, the cost increases with increasing doses of chemicals and power applied. The overall cost is higher for the treatment of acrylic effluent, followed by cotton and the polyester, which is related to the amount of hydrogen peroxide used (the acrylic requires a higher concentration of this reagent and the polyester a lower dose). For this reason, the weight of the chemicals in the overall cost also varies from effluent to effluent, being very relevant in the acrylic one, while in the polyester the radiation intensity is preponderant. Chapter 9 – Simulated Dyeing Textile Effluents Treatment by the Photo - Fenton Process 226 a) b) c) Figure 9.4 – Effect of hydrogen peroxide doses and radiation intensity on the total operating cost associated with the photo-Fenton process with TQ 150 lamp for treating acrylic (a), cotton (b) and polyester (c) wastewaters. 0 10 20 0 10 20 30 40 0167 333 500 Operating Cost (€/m 3 ) Light flux (W/m 2 ) 30-40 20-30 10-20 0-10 0 5 10 0 10 20 30 40 0167 333 500 Operating Cost (€/m 3 ) Light flux (W/m 2 ) 30-40 20-30 10-20 0-10 0 1.25 2.5 0 10 20 30 40 0167 333 500 Operating Cost (€/m 3 ) Light flux (W/m 2 ) 30-40 20-30 10-20 0-10 Part III 227 The main purpose of this analysis was to find which set of conditions described in the previous section and that allow reaching a final effluent complying with legislated standards provide a smaller cost. Values obtained for such costs are included in Table 9.1. It can be seen that the conditions providing smaller costs for each effluent but still complying with legislation are the following: i) acrylic – [H 2 O 2 ] = 10.0 g/L, intensity = 220 W/m 2 , cost = 17.4 €/m 3 ; ii) cotton – [H 2 O 2 ] = 10.0 g/L, intensity = 7 W/m 2 , cost = 9.6 €/m 3 ; iii) polyester – [H 2 O 2 ] = 2.5 g/L, intensity = 7 W/m 2 , cost = 2.9 €/m 3 . For all effluents, but particularly for the acrylic and cotton ones, the treatment costs are quite high. Therefore, with the purpose of minimizing the costs, namely in terms of energy, the work proceeded by testing the photo-Fenton process with simulated solar radiation (for which energy costs are null). 9.3.2 Photoreactor with Simulated Solar Radiation Tests were carried out as when using lamp TQ 150 with the purpose of not exceeding the maximum allowable values for the treated effluents, with the exception that with the Solarbox it was not possible to decrease the radiation intensity bellow 253 W/m 2 (lamp power = 76 W ). On the other hand, values above 500 W/m 2 (lamp power = 150 W) were also not tested. First, to compare with data obtained with TQ lamp, but also to keep at reasonable levels the power corresponding to the radiation intensity close to real conditions (150 W correspond to ~ 60 W/m 2 at wavelengths in the range 300-400 nm, which is only slightly above the typical maximum radiation intensity in the north of Portugal – 50 W/m 2 ). 9.3.2.1 Effect of Hydrogen Peroxide Concentration Results of color and DOC removals obtained for runs with the Solarbox employing a radiation intensity of 253 W/m 2 at different dosages of oxidant are shown in Figure 9.5. For both the acrylic and cotton dyeing wastewaters the color removal is very rapid (only 12 minutes are required for complete decolorization at all doses tested). However, for DOC removal it is necessary more time, and again after ~60 minutes the maximum performance is reached, which is not further improved. Better performances are reached Chapter 9 – Simulated Dyeing Textile Effluents Treatment by the Photo - Fenton Process 228 for higher H 2 O 2 doses: 82.4% for 20 g/L of H 2 O 2 in the acrylic; 54.6% for 10 g/L in the cotton, and 66.3% for 2.5 g/L for the polyester. a) b) c) Figure 9.5 – Effect of H 2 O 2 dose on DOC and color removal with simulated solar radiation at intensity of 253 W/m 2 for acrylic (a), cotton (b) and polyester (c) wastewaters (T=50 ºC, Fe 2+ :H 2 O 2 acrylic =1:57, Fe 2+ :H 2 O 2 cotton =1:33 Fe 2+ :H 2 O 2 polyester =1:7, pH=3.5). 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 10 g/L H2O2 20 g/L H2O2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 5 g/L H2O2 10 g/L H2O2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 1.25 g/L H2O2 2.5 g/L H2O2 Part III 229 Again, the final COD, BOD 5 and visible color (after dilution of 1:40) after 60 minutes of reaction were measured for each effluent (see Table 9.2). It is worth noting that in all tests with radiation intensity of 253 W/m 2 the effluents does not exhibit visible color, and the values of the other two parameters are smaller than the maximum allowable values. So, it is possible to decrease the oxidant dose in each case, possibly requiring however a higher radiation intensity. This does not imply however higher costs, once we are now using solar radiation (although simulated). Table 9.2 – Values of COD, BOD 5 and visible color (1:40 dilution) after 60 minutes of oxidation for different doses of H 2 O 2 and radiation intensityes using simulated solar irradiation (in bold: conditions that allow meeting the discharge limits at the minimum cost). [H 2 O 2 ] (g/L) Radiation intensity (W/m 2 ) COD (mgO 2 /L) BOD 5 (mgO 2 /L) Visible color after dilution 1:40 Total Costs (€/m 3 ) Acrylic 6.5 500 232.1 32.4 not visible 5.8 10.0 253 242.0 44.6 not visible 9.2 500 143.2 33.1 not visible 9.2 20.0 253 150.6 40.8 not visible 18.3 500 101.2 55.8 not visible Cotton 3.75 500 244.5 76.3 not visible 3.5 5.0 253 207.8 75.0 not visible 4.7 500 183.4 80.9 not visible 4.7 10.0 253 158.9 79.3 not visible 9.3 500 134.5 83.5 not visible 9.3 Polyester 0.938 150 231.0 66.4 not visible 1.0 1.25 76 221.1 74.3 not visible 1.3 150 206.4 61.4 not visible 1.3 2.5 76 179.4 60.8 not visible 2.7 150 167.1 57.6 not visible 2.7 Chapter 9 – Simulated Dyeing Textile Effluents Treatment by the Photo - Fenton Process 230 The trends reached with the maximum solar radiation intensity of 500 w/m 2 for different hydrogen peroxide doses are nearly the same as before (cf. Figure A.7 in Appendix): color removal is very quick, requiring only 1 to 5 minutes of exposure to radiation to reach values > 99%; removal of DOC is again very fast mainly in the first 15 minutes, and nearly stabilizes after 60 minutes of irradiation; higher performances are reached for increased amount of reagents used. Mineralization achieved was 91.7% for the acrylic effluent using 20 g/L of H 2 O 2 ; ~64% for the cotton one with 10 g H 2 O 2 /L and 71.2% at a dose of 2.5 g H 2 O 2 /L for the polyester one. As expected, DOC removals are higher at 500 W/m 2 vs. 253 W/m 2 , for the same doses of reagents. For all effluents and after exposure to irradiation during 60 minutes, the remaining loads of COD, BOD 5 and visible color visible are shown in Table 9.2. Again, in all tests the effluents are colorless, and the values of the other two parameters are still smaller than the legislated standards (100 mgO 2 /L for BOD 5 and 250 mgO 2 /L for COD). Finally, it is worth mentioning that performances reached (in terms of COD, BOD 5 , DOC and color removal) in the all tests performed with the simulated solar radiation are very close to those obtained with the TQ150 lamp (of course data must be compared for identical conditions, i.e., doses of chemicals and radiation intensity, for every effluent). 9.3.2.2 Operating Costs In the treatment of the wastewaters by photo-Fenton oxidation with simulated solar radiation, as stated earlier, for the calculation of the total cost of operation only the consumption of reagents was taken into account (Equations. 9.2 and 9.3), while the energy costs (Equation 9.4) were assumed to be null. Figure 9.6 shows the effect of hydrogen peroxide and ferrous ion concentrations in the wastewaters treatment cost. Both reactants increase total costs, however this is far more influenced by the H 2 O 2 dose. Obviously, for the acrylic higher costs are reached, while the smaller are for the polyester, because of the different ranges of hydrogen peroxide concentrations employed. It is also noteworthy that the costs are much smaller than in the photo-Fenton using the TQ 150 lamp (Figure 9.5), where energy costs were also taken into account. Part III 231 a) b) c) Figure 9.6 – Effect of H 2 O 2 and Fe 2+ doses on the total operating cost associated with the photoFenton with simulated solar radiation for treating acrylic (a), cotton (b) and polyester (c) wastewaters. 0 10 20 0 5 10 15 20 0175 350 Operating Cost (€/m 3 ) [Fe 2+ ] (mg/L) 15-20 10-15 5-10 0-5 0 5 10 0 3 5 8 10 0150 300 Operating Cost (€/m 3 ) [Fe 2+ ] (mg/L) 8-10 5-8 3-5 0-3 0 1.25 2.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0175 350 Operating Cost (€/m 3 ) [Fe 2+ ] (mg/L) 2.5-3.0 2.0-2.5 1.5-2.0 1.0-1.5 0.5-1.0 0.0-0.5 Chapter 10 – Simulated Textile Dyeing Effluents Treatment by SBR alone and Combined with Fenton’s Oxidation 238 10.2.3 Analytical Methods The analytical methods used for the determination of the various parameters are described in section 3.3 of chapter 3. All determinations were performed in duplicate and the coefficients of variation were less than to 2% for DOC, 8% for BOD 5 , 4% for COD and SOUR, 3% for inhibition of V. fisheri and 5% for the other parameters. 10.3 Results and Discussion The more relevant characteristics of the synthetic acrylic, cotton and polyester dyeing wastewaters used in this study are reported in Table 3.4. Cotton and acrylic wastewaters are colored even at 1:40 dilution but polyester effluent is practically colorless. The organic load (expressed as COD or DOC) is moderate for all wastewaters but the biodegradability is low as indicated by the BOD 5 :COD ratio and the values of SOUR; actually, the acrylic wastewater can be classified as non biodegradable and the other wastewaters can be considered as only slightly biodegradable. Acrylic and polyester effluents strongly inhibit V. fisheri activity, which proves their toxicity. Taking into account the low biodegradability and the high toxicity (except for the cotton wastewater), a biological treatment of these wastewaters does not probably allow meeting the discharge limits, as established by the Portuguese legislation (cf. Table 3.4). Even so, the feasibility of using a biological process (SBR) alone or downstream from a chemical oxidation process (Fenton’s reaction) to achieve the discharge limits was investigated in this study. The results obtained when applying this strategy for treating the three different kinds of textile dyeing wastewaters are shown in the next sections. 10.3.1 Biological Treatment The biological degradation was only applied to raw polyester and cotton effluents because the acrylic one presents very low biodegradability (BOD 5 /COD ratio <0.0012 and SOUR Part III 239 <0.2 – Table 3.4), also confirmed by the Zhan Wellens test (see Figure 10.1), which indicated that the degradation obtained after 28 days does not exceed 15%. Figure 10.1 – Evolution of percentage of COD degradation along time in Zahn-Wellens test for acrylic wastewater. Figure 10.2 shows the COD, BOD 5 , DOC, total nitrogen and color removals obtained in 10 successive cycles of SBR treatment of polyester and cotton effluents; no further cycles were applied because nearly steady-state conditions were reached in all cases, i.e., stable performances in consecutive cycles. The polyester effluent exhibits a considerable increase of COD, BOD 5 , DOC and total nitrogen removal during the first 5 cycles that continue to increase, albeit more slowly, up to the 7th cycle, and then remain almost constant with average values of 24.2, 39.4, 39.7 and 16.4% for COD, BOD 5 , DOC and nitrogen, respectively. For the cotton effluent the removals also increase during the first 5 cycles and then the removal rate decreases or maintains constant leading to average final values of 19.9, 19.6, 19.9 and 20.5% for COD, BOD 5 , DOC and nitrogen, respectively. The low efficiencies achieved can be explained by the presence in the effluents of a significant proportion of refractory or only slightly biodegradable compounds, as could be inferred from the low BOD 5 /COD ratios and SOUR values, particularly for the cotton one (cf. Table 3.4). As regards color removal, in the cotton wastewater the values of absorbance at 520 nm decreased in the first 4 cycles and kept constant in the subsequently cycles, achieving an average value of 50.6% of decolorization. The removal may be the result of some biological degradation of the textile dyes present in the effluent 0 20 40 60 80 100 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Dt (%) t (days) Control Substance Wastewater Chapter 10 – Simulated Textile Dyeing Effluents Treatment by SBR alone and Combined with Fenton’s Oxidation 240 but the adsorption onto the biomass flocs probably also contributes for color elimination [Waters, 1995]. The color removal obtained for cotton wastewater is similar to that reported by Vaigan et al. [2009]. These authors achieved color removals of 31-57% when treating 20 to 40 mg/L of reactive Blue B-16, respectively, in an SBR. Figure 10.2 - Variation of COD (a), BOD 5 (b), DOC (c), total nitrogen (d) and color (e) removals along 10 cycles of SBR operation for polyester and cotton wastewaters. 0 20 40 60 0 1 2 3 4 5 6 7 8 9 10 COD removal (%) Number of Cycles a) 0 20 40 60 0 1 2 3 4 5 6 7 8 9 10 BOD 5 removal (%) Number of Cycles b) 0 20 40 60 0 1 2 3 4 5 6 7 8 9 10 DOC removal (%) Number of Cycles c) 0 20 40 60 012345678910 Ntotal removal (%) Number of Cycles d) 0 20 40 60 012345678910 Color removal (%) Number of Cycles e) Polyester Cotton Part III 241 With regard to other monitored parameters, whose values are not presented in Figure 10.2, it was noted that during all SBR cycles the concentrations in the treated effluents were in the range 2.4 - 2.9 mg P/L, 22 – 29 mg TSS/L and 2530-2970 mg VSS/L for the polyester effluent and 5.7 - 5.9 mg P/L, 27 - 32 mg TSS/L and 2350-2680 mg VSS/L for the cotton one. The pseudo-steady state was reached after ca. 7 cycles for both cotton and polyester effluents. Table 10.1 presents the average values of different parameters after reaching the pseudo-steady state. It can be concluded that the effluents resulting from biological treatment do not meet the discharge limits, since the values of COD (392.4 and 280.4 mg/L for polyester and cotton, respectively) are above 250 mg/L and the color of the cotton effluent is visible after 1:40 dilution. So, a pre-treatment or subsequent treatment is required. We choose to apply the chemical oxidation by Fenton’s reagent as pre-treatment to enhance the biodegradability and remove color and, then, subject the wastewater to biological treatment. The results obtained from the combined process are presented in the following section. Chapter 10 – Simulated Textile Dyeing Effluents Treatment by SBR alone and Combined with Fenton’s Oxidation 242 Table 10.1 – Characteristics of the simulated dyeing raw wastewaters and after SBR treatment and respective removal efficiencies. Parameter Acrylic Polyester Cotton Maximum Allowable Value* Raw Wastewater Raw Wastewater After SBR Removal (%) Raw Wastewater After SBR Removal (%) pH 6.8 8.3 7.10 --- 11.4 7.15 --- 5.5-9.0 Conductivity at 20 ºC (mS/cm) 1503.0 2.9 n.d. --- 23.2 n.d. --- Total suspended solids (mg/L) 16.0 21.7 25.1 67.0 28.3 Total nitrogen (mg N/L) 16.4 15.9 13.3 16.4 3.9 3.1 20.5 Nitrates (mg NO 3- /L) 15.7 7.5 n.d. --- 4.25 n.d. --- Total phosphorus (mg P/L) 0.2 3.0 2.4 20.0 5.9 5.7 3.4 Dissolved phosphorus (mg P/L) < 0.06 2.7 n.d. --- 0.1 n.d. --- COD – Chemical oxygen demand (mg O 2 /L) 828.1 517.9 392.4 24.2 350.0 280.4 19.9 250 BOD 5 – Biochemical oxygen demand (mg O 2 /L) < 1.0 130.7 79.1 39.4 77.5 62.3 19.6 100 DOC – Dissolved organic carbon (mg C/L) 334.1 143.1 86.3 39.7 117.5 94.1 19.9 Sulfates (mg/L) 598.0 885.8 n.d. --- 41.0 n.d. --- Chlorides (mg Cl - /L) 44.1 17.3 n.d. --- 7981.8 n.d. --- Alkalinity (mg CaCO 3 /L) 51.8 774.4 n.d. --- 4425.0 n.d. --- SOUR – Specific oxygen uptake rate (mg O 2 /(g VSS .h)) < 0.2 27.0 n.d. --- 5.6 n.d. --- BOD 5 :COD ratio < 0.0012 0.26 0.20 --- 0.22 0.22 --- Maximum absorbance wavelength, λ max (nm) 610 --- n.d. --- 520 n.d. Absorbance at λ max (a.u.) 1.592 --- n.d. --- 0.437 0.179 50.6** Visible color after dilution 1:40 Visible not visible not visible --- Visible visible --- not visible Vibrio fischeri Inhibition 5 min (%) 94.0 74.5 n.d. --- 0.0 n.d. --- Vibrio fischeri Inhibition 15 min (%) 96.0 82.5 n.d. --- 0.0 n.d. --- Vibrio fischeri Inhibition 30 min (%) 97.0 84.5 n.d. --- 0.0 n.d. --- n.d. – not determined * Portuguese legislation for discharge of textile wastewaters (Ordinance No. 423/97 of 25 June ). ** calculated from the absorbance of raw wastewater at pH 7.0 (0.3617 abs. units) Part I II 243 10.3.2 Integration of Fenton’s Reagent Followed by Biological Treatment As the oxidation process allows increasing the biodegradability of the acrylic and cotton effluents while reducing the toxicity of the acrylic and polyester effluents, as shown below (cf. Tables 10.2-10.4), the combination of Fenton reaction with the biological oxidation in SBR was studied. Aiming reducing the doses of chemicals, and inherently the operating costs (described in the following section), three experiments were performed, i.e., the preliminary Fenton reaction stage was performed with different doses of reagents. The 1st run was performed at the best conditions for maximizing color and DOC removals and improving biodegradability already determined in previous studies (chapters 6-8): [H 2 O 2 ]=20 g/L and [Fe 2+ ]=350 mg/L for acrylic, [H 2 O 2 ]=10 g/L and [Fe 2+ ]=300 mg/L for cotton and [H 2 O 2 ]=2.5 g/L and [Fe 2+ ]=350 mg/L for polyester wastewaters, all at pH 3.5 and 50 ºC. In runs #2 and #3 the doses of hydrogen peroxide and ferrous iron were reduced to 3/4 and 1/2 for acrylic and 1/2 and 1/4 for polyester and cotton effluents, respectively, with the aim of decreasing the treatment cost (associated with the consumption of chemicals in the Fenton’s process) while obtaining a final effluent that should meet the discharge limits imposed by the national legislation for the textile industry. Results obtained during Fenton’s oxidation have been reported previously (in the works mentioned above) and only overall performances reached are described herein – run #1 in Tables 10.2, 10.3 and 10.4 for the acrylic, cotton and polyester effluents, respectively. Chapter 10 – Simulated Textile Dyeing Effluents Treatment by SBR alone and Combined with Fenton’s Oxidation 244 Table 10.2 – Characteristics of the synthetic acrylic dyeing wastewaters after Fenton reaction and SBR and respective removal efficiencies (within brackets) and global removals. Runs#1 to #3 represent experiments with decreasing doses of chemicals in the Fenton’s stage. Parameter Run #1 – Optimal dose of chemicals Run #2 – 0.75 of optimal dose of chemicals Run #3 – 0.5 of optimal dose of chemicals Maximum Allowable Value* Fenton (removal (%)) SBR (removal (%)) Global Removal (%) Fenton (removal (%)) SBR (removal (%)) Global Removal (%) Fenton (removal (%)) SBR (removal (%)) Global Removal (%) pH 7.10 7.15 --- 7.06 7.09 --- 7.01 6.98 --- 5.5-9.0 Total nitrogen (mg N/L) 16.0 (2.4) 8.8 (45.0) 46.3 16.1 (2.4) 9.3 (41.9) 43.3 16.3 (2.4) 12.4 (22.5) 24.4 Total phosphorus (mg P/L) 0.2 (0.0) 0.61 (47.9**) 47.9 0.2 (0.0) 0.20 (74.7**) 74.7 0.2 (0.0) 0.16 (68.0**) 68.0 COD (mg O 2 /L) 289.0 (65.1) 14.6 (94.9) 98.2 294.5 (64.4) 104.3 (64.6) 87.4 349.7 (57.7) 273.7 (21.8) 66.9 250 BOD 5 (mg O 2 /L) 116.5 6.4 (94.5) 94.5 78.8 12.0 (84.8) 84.8 46.8 14.5 (69.0) 69.0 100 DOC (mg C/L) 112.0 (66.5) 5.4 (95.2) 98.4 124.7 (62.7) 34.5 (72.3) 89.7 132.3 (60.4) 109.3 (17.4) 67.3 SOUR – Specific oxygen uptake rate (mg O 2 /(g VSS .h)) 17.9 n.d. --- 10.2 n.d. --- 2.7 n.d. --- BOD 5 :COD ratio 0.40 0.46 --- 0.27 0.12 --- 0.13 0.05 --- Absorbance at λ max (a.u.) 0.0079 (99.5***) 0.0025 (68.4****) 99.8 0.0080 (99.5***) 0.0025 (68.8****) 99.8 0.0089 (99.4***) 0.0025(71.9** **) 99.8 Visible color after dilution 1:40 not visible not visible --- not visible not visible --- not visible not visible --- not visible Vibrio fischeri Inhibition 5 min (%) 29 n.d. --- 38 n.d. --- 77 n.d. --- Vibrio fischeri Inhibition 15 min (%) 27 n.d. --- 41 n.d. --- 81 n.d. --- Vibrio fischeri Inhibition 30 min (%) 29 n.d. --- 41 n.d. --- 82 n.d. --- n.d. – not determined. * Portuguese legislation for discharge of textile wastewaters (Ordinance No. 423/97 of 25 June). ** calculated from total phosphorus in effluent after Fenton reaction after adding phosphate buffer (1.17, 0.79, 0.5 mg P/L in run #1, #2, #3, respectively). *** calculated from the absorbance at 610 nm of raw wastewater at pH 3.5 (1.624 abs. units). **** calculated from the absorbance at 610 nm of wastewater after Fenton at pH 7.0 (0.0079, 0.0080 and 0.0089 abs. units in run #1, #2 and #3, respectively). Part III 245 Table 10.3 – Characteristics of the synthetic cotton dyeing wastewater after Fenton reaction and SBR and respective removal efficiencies (within brackets) and global removals. Runs#1 to #3 represent experiments with decreasing doses of chemicals in the Fenton’s stage. Parameter Run #1– Optimal dose of chemicals Run #2 – 0.5 of optimal dose of chemicals Run #3 – 0.25 of optimal dose of chemicals Maximum Allowable Value* Fenton (removal (%)) SBR (removal (%)) Global Removal (%) Fenton (removal (%)) SBR (removal (%)) Global Removal (%) Fenton (removal (%)) SBR (removal (%)) Global Removal (%) pH 6.99 7.05 --- 7.04 7.10 --- 7.09 7.03 --- 5.5-9.0 Total nitrogen (mg N/L) 3.9 (0.0) 1.2 (82.4) 82.4 3.9 (0.0) 2.1 (62.5) 62.5 3.8 (2.6) 3.7 (15.9) 18.1 Total phosphorus (mg P/L) 5.9 (0.0) 4.8 (18.6) 18.6 5.9 (0.0) 5.2 (11.9) 11.9 5.8 (1.7) 5.6 (3.4) 5.1 COD (mg O 2 /L) 262.1 (25.1) 43.2 (83.5) 87.7 281.9 (19.5) 113.2 (59.8) 67.7 318.6 (9.0) 261.8 (17.8) 25.2 250 BOD 5 (mg O 2 /L) 135.7 (0.0) 22.8 (83.2) 83.2 112.9 (0.0) 45.1 (60.1) 60.1 88.0 (0.0) 72.3 (17.8) 17.8 100 DOC (mg C/L) 60.2 (48.8) 9.95 (83.5) 91.5 94.1 (19.9) 37.6 (60.0) 68.0 100.3 (14.6) 82.0 (18.2) 30.2 SOUR – Specific oxygen uptake rate (mg O 2 /(g VSS .h)) 15.51 n.d. --- 8.11 n.d. --- 2.54 n.d. --- BOD 5 :COD ratio 0.52 0.53 --- 0.40 0.40 --- 0.33 0.28 --- Absorbance at λ max (a.u.) 0.0331 (89.9***) 0.0037 (86.6****) 98.6 0.0310 (90.5***) 0.0053 (81.9****) 98.3 0.0349 (89.3***) 0.0126 (65.8****) 96.3 Visible color after dilution 1:40 not visible not visible --- not visible not visible --- not visible not visible --- not visible Vibrio fischeri Inhibition 5 min (%) 0.0 n.d. --- 0.0 n.d. --- 0.0 n.d. --- Vibrio fischeri Inhibition 15 min (%) 0.0 n.d. --- 0.0 n.d. --- 0.0 n.d. --- Vibrio fischeri Inhibition 30 min (%) 0.0 n.d. --- 0.0 n.d. --- 0.0 n.d. --- n.d. – not determined. * Portuguese legislation for discharge of textile wastewaters (Ordinance No. 423/97 of 25 June). ** calculated from total phosphorus in effluent after Fenton reaction after adding urea ( 6.8, 5.6, 4.4 mg N/L in run #1, #2, #3, respectively). *** calculated from the absorbance at 520 nm of raw wastewater at pH 3.5 (0.3615 abs. units). **** calculated from the absorbance at 520 nm of wastewater after Fenton at pH 7.0 ( 0.0276, 0.0293 and 0.0368 abs. units in run #1, #2 and #3, respectively). Chapter 10 – Simulated Textile Dyeing Effluents Treatment by SBR alone and Combined with Fenton’s Oxidation 246 Table 10.4 – Characteristics of the synthetic polyester dyeing wastewaters after Fenton reaction and SBR and respective removal efficiencies (within brackets), and global removals. Runs#1 to #3 represent experiments with decreasing doses of chemicals in the Fenton’s stage. Parameter Run #1 – Optimal dose of chemicals Run #2 – 0.5 of optimal dose of chemicals Run #3– 0.25 of optimal dose of chemicals Maximum Allowable Value* Fenton (removal (%)) SBR (removal (%)) Global Removal (%) Fenton (removal (%)) SBR (removal (%)) Global Removal (%) Fenton (removal (%)) SBR (removal (%)) Global Removal (%) pH 7.05 7.10 --- 7.11 7.08 --- 7.15 7.10 --- 5.5-9.0 Total nitrogen (mg N/L) 15.1 (5.0) 12.3 (18.5) 22.6 15.3 (3.8) 12.4 (19.0) 22.0 15.9 (0.0) 13.3 (16.4) 16.4 Total phosphorus (mg P/L) 2.8 (6.7) 2.2 (20.0) 25.3 2.9 (3.3) 2.2 (22.8) 25.3 3.0 (0.0) 2.4 (20.3) 20.3 COD (mg O 2 /L) 221.1 (57.3) 44.4 (79.9) 91.4 291.7 (43.7) 104.3 (64.2) 79.9 389.7 (24.7) 267.7 (31.3) 48.3 250 BOD 5 (mg O 2 /L) 62.8 (52.0) 11.4 (81.8) 91.3 80.2 (38.6) 29.4 (63.4) 77.5 103.8 (20.6) 54.3 (47.7) 58.5 100 DOC (mg C/L) 63.4 (55.7) 12.6 (80.1) 91.2 80.6 (43.7) 27.7 (65.6) 80.6 106.9 (25.3) 58.1 (45.7) 59.4 SOUR – Specific oxygen uptake rate (mg O 2 /(g VSS .h)) 30.0 n.d. --- 29.0 n.d. --- 28.1 n.d. --- BOD 5 :COD ratio 0.28 0.26 --- 0.28 0.28 --- 0.27 0.20 --- Visible color after dilution 1:40 not visible not visible --- not visible not visible --- not visible not visible --- not visible Vibrio fischeri Inhibition 5 min (%) 0.0 n.d. --- 10.4 n.d. --- 43.3 n.d. --- Vibrio fischeri Inhibition 15 min (%) 0.0 n.d. --- 15.0 n.d. --- 55.8 n.d. --- Vibrio fischeri Inhibition 30 min (%) 0.0 n.d. --- 17.6 n.d. --- 59.4 n.d. --- n.d. – not determined. * Portuguese legislation for discharge of textile wastewaters (Ordinance No. 423/97 of 25 June). Part III 247 Regarding the results obtained in the SBR, Figure 10.3 shows the removal performances achieved, in terms of COD, BOD 5 , DOC, total nitrogen and color, for the acrylic wastewater. It can be observed that removals increased during the first 4 cycles, although the improvement is more notorious in the 1 st and 2 nd runs; therefore, we can say that the pseudo-steady state was reached at end of 4-5 cycles. After reaching the pseudo-steady sate, the average removals achieved in the SBR for the parameters analyzed are higher in run #1 (94.9, 94.5, 95.2, 45.0 and 68.4% for COD, BOD 5 , DOC, total nitrogen and color, respectively), followed by run #2 (64.6, 84.8, 72.3, 41.9 and 68.8% for COD, BOD 5 , DOC, total nitrogen and color, respectively) and then by run #3 (21.8, 69.0, 17.4, 22.5 and 71.9% for COD, BOD 5 , DOC, total nitrogen and color, respectively). The reason is that from run #1 to run #3 less chemicals were used in the Fenton’s stage, so that the effluent fed to the SBR is less biodegradable (cf. Table 10.2). In runs #1 and #2 it was possible to reach, after the integrated treatment, an effluent that is ready for discharge into water bodies – see Table 10.2. On the other hand, although in run #3 less chemicals were employed in the Fenton’s stage as compared to run #2, it was not possible to fulfill the limits imposed by the national legislation for the discharge of textile effluents, namely in terms of COD (cf. Table 10.2). The removals obtained during 10 cycles of SBR for the cotton effluent previously treated by Fenton’s oxidation are shown in Figure 10.3. During the first 6 cycles an increase was observed for all runs, and then the removals remain nearly constant, which means that the pseudo-steady state was reached. In runs #1 and #2 the average values of COD, BOD 5 and visible color (after dilution of 1:40) at the outlet of the SBR, during the last 4 cycles of operation, are smaller than the maximum allowable discharge values (see Table 10.3). This is however not the case of run #3, in which very low doses of chemicals were used in the Fenton’s oxidation (25% of those employed in run #1); thus, final effluent shows COD values not complying with the legislated standard. Part IV Real Cotton Dyeing Wastewater * This Chapter is based on the publication “Rodrigues C.S.D.; Madeira, L.M.; Boaventura, R.A.R. Decontamination of an industrial cotton dyeing wastewater by chemical and biological processes”. Submitted to Industrial & Engineering Chemistry Research. Chapter 11 Cotton Dyeing Wastewater Treatment * Part IV 259 11 Cotton Dyeing Wastewater Treatment 11.1 Introduction This work aimed at evaluating four approaches for treating a real cotton dyeing wastewater (see Figure 11.1). In Approach 1 coagulation/flocculation was combined with Fenton’s reaction (as coagulation/flocculation per se is not effective to comply with legislated discharge standards for textile wastewater under study, as detailed below). In Approach 2 only Fenton’s oxidation was applied and in Approaches 3 and 4 the wastewater was pre-treated by Fenton’s oxidation and then treated by coagulation/flocculation and a biological process (SBR), respectively. In all situations it was intended to obtain the lowest operating cost and an effluent that meets the discharge limits imposed by the national legislation for textile effluents. Therefore, to reduce costs, part of the catalyst used in the Fenton’s reaction of Approach 1 was the residual dissolved iron resulting from coagulation/flocculation (this methodology has been already applied to industrial wastewaters other than textile dyeing ones) [Peres et al., 2004; Xing and Sun, 2009; Perdigon-Melon et al., 2010]. In the same way, in Approach 3 the coagulant used was the residual iron resulting from the Fenton’s reaction; however, in this case the final effluent clearly complied with legislated standards, and so the Fenton’s stage was also performed with doses of chemicals reduced to 3/4 and 1/2 of the optimum value found in Approach 2 (this methodology has not yet been described in the literature). In Approach 4 the doses of reagents used in the Fenton’s oxidation were also reduced, as described above, and the resulting effluent was subjected to a biological process. It has been reported in literature [Oller et al., 2011] the need of using oxidative processes as a pretreatment step of industrial textile wastewaters with the aim of generating a biodegradable effluent without extensive testing the behavior of the biological process. Recent works already integrated both processes, particularly combining Fenton’s oxidation and biological degradation in SBR [Rodrigues et al., 2009 a); Blanco et al., 2012; Elmolla and Chaudhuri, 2012; Sanchis et al., 2013; Wu et al., 2013]. The ultimate choice of the technology to adopt should take also into account economic indicators, and so a cost analysis was performed for each treatment strategy, as detailed in the next section. Chapter 11 – Cotton Dyeing Wastewater Treatment 260 Approach 1: Coagulation/flocculation followed by Fenton’s reaction Approach 2: Fenton’s oxidation alone Approach 3: Fenton’s oxidation followed by coagulation/flocculation Approach 4: Integration of Fenton’s oxidation plus SBR Figure 11.1 - Schematic diagram of all process configurations adopted. Run #1: 18.8 mg/L Fe 2+ and 0.625 mg/L H 2 O 2 in Fenton’s oxidation Run #2: 28.2 mg/L Fe 2+ and 0.938 mg/L H 2 O 2 in Fenton’s oxidation Run #3: 37.5 mg/L Fe 2+ and 1.25 mg/L H 2 O 2 in Fenton’s oxidation Approaches 3 and 4 Fenton Fenton Coagulation /Flocculatio 200 mg/L Fe 2+ 98.3 mg/L Fe 2+ 37.5 or 300 mg/L Fe 2+ 0.938 - 10 g/L H 2 O 2 Effluent Real Dyeing Effluent Real Dyeing Fe 2+ H 2 O 2 SBR Fenton Coagulation/ Flocculation Fenton 2.5 mg/L Magnafloc 155 Effluent Real Dyeing Fe 2+ H 2 O 2 Effluent Real Dyeing Part IV 261 11.2 Operating Costs To select the better integration of stages for wastewater treatment, but ensuring that the generated effluent meets the discharge standards, the operating costs associated to the consumption of chemicals and energy were also assessed. For the latter it was considered the energy consumed in agitation (power required = 0.61 W) and air insufflated (power = 4.5 W) in the SBR stage. The costs of acids and base were not considered as they are almost negligible compared to the other chemicals. In the economic analysis the costs of reagents were those given by Quimitécnica S.A. and Rivaz Química S.A.: H 2 O 2 (49.5% (w/v), density at 25 ºC = 1.2 g/cm 3 ) – 365 €/ton; FeSO 4 .7H 2 O (93 wt.% of purity) – 233.7 €/ton; and Magnafloc 155 – 3850 €/ton. For energy it was considered the average value of 0.10 €/(kW h)). The operating cost for the coagulation/flocculation step is the sum of costs of Fe 2+ (Equation 11.1) and Magnafloc 155 (Equation 11.2), while for Fenton’s reaction is the sum of costs of Fe 2+ (Equation 11.1) and H 2 O 2 (Equation11.3) consumption; finally, for SBR is the cost of energy (Equation 11.4) only. (11.4) ) 3 (m effluent treated Volume (h) aeration time * h) (kW energy Price * (kW) 310* ) agitation required Power dinsufflate air (Power energy Cost (11.3) (kg/L) 100 2 O 2 H % ) L kg ( 2 O 2 H ρ * ) 3 m ton ( 3 10* 2 O 2 H * ) ton € ( 2 O 2 H Price 2 O 2 H Cost (11.2) ) 3 m ton ( 6 10*155Magnafloc * ) ton € ( 155Magnafloc Price 155Magnafloc Cost (11.1) 100 purity of % 2 Fe MM O 2 7H 4 FeSO MM * ) 3 m ton ( 6 10* 2 Fe * ) ton € ( O 2 7H 4 FeSO Price 2 Fe Cost + = − = − = + −+ = +                                                     Chapter 11 – Cotton Dyeing Wastewater Treatment 262 In the previous Equations, [i] represents the concentration of species i (in g/L for H 2 O 2 and mg/L for Fe 2+ and Magnafloc 155), MM i stands for molar mass (in g/mol) and the power required for agitation is expressed in W. The total operating costs for the integrated processes are calculated by the sum of costs associated with each process involved. 11.3 Materials and Methods 11.3.1 Experimental Procedure The coagulation/flocculation, Fenton’s reaction and SBR experiments were performed as detailed in sections 3.4.1, 3.4.2 and 3.4.4, respectively. The supernatant resulting from coagulation/flocculation was collected and acidified with HNO 3 (68%, from Merck, Germany) to pH < 4 to keep the iron dissolved (to be later used as catalyst in the Fenton’s reaction), when treating the effluent by the combination of coagulation/flocculation plus Fenton’s reaction. When applying Fenton’s oxidation followed by coagulation/flocculation, the effluent from the oxidation stage was acidified to pH ≈ 1 to keep the iron dissolved for the coagulation/flocculation study, while simultaneously slowing down or inhibiting the Fenton’s reaction. The analyses of the effluent were performed immediately. All coagulation/flocculation experiments were conducted at room temperature (22-24 ºC). All operating conditions were set taking into account previous results achieved with a similar simulated effluent (chapter 7). 11.3.2 Analytical Methods All analytical parameters were determined as described in section 3.3 of chapter 3. The analytical determinations were performed in duplicate, and the coefficients of variation were less than 2% for DOC, 6% for BOD 5 , 4% for COD and k’, and 5% for the other parameters. Part IV 263 11.4 Results and Discussion 11.4.1 Textile Deying Wastewater The industrial cotton deying watewater was provided by Têxtil Luis Simões S.A. and its main characteristics are reported in Table 3.5 (section 3.2.2). 11.4.2 Coagulation/Flocculation plus Fenton’s Reaction (Approach 1) This study started with the application of coagulation/flocculation to the raw wastewater, using ferrous sulfate and Maganafloc 155 as coagulant and flocculant, respectively. The operating conditions used were the optimal ones determined in a prior study on the treatment of a synthetic cotton wastewater (chapter 4): V coagulation =150 rpm, t coagulation = 3 min, [Fe 2+ ]= 200 mg/L, pH= 9.4, V flocculation =20 rpm, t flocculation = 15 min, [Magnafloc 155] = 0.5 mg/L. The characteristics of the wastewater after treatment are presented in Table 11.1. One can conclude that coagulation/flocculation is very efficient as regards color removal (95.1% - percent removal efficiencies are within brackets in the table), leads to a considerable removal of organic matter (36.9% and 39.4% respectively for COD and DOC) and phosphorus (47.2%), but it is quite inefficient concerning the removal of BOD 5 (17.2%) and nitrogen (1.9%). Moreover, the values of COD and BOD 5 in the final effluent are above the discharge standards imposed by the Portuguese legislation, which makes necessary an additional treatment. So, for increasing the efficiency of organic matter removal, the effluent from the coagulation/flocculation stage was subjected to Fenton’s oxidation, applying the operating conditions already optimized when treating a synthetic effluent by the same integrated process (chapter 7): T= 50 ºC, pH= 3.5, t= 60 min, [H 2 O 2 ]= 500 mg/L and [Fe 2+ ] added = 98.3 mg/L (total iron concentration = 100 mg/L, taking into account that 1.7 mg Fe/L remained from the coagulation/flocculation step). Results included in Table 11.1 point out that Fenton’s oxidation applied to the pre-treated effluent allowed obtaining COD, BOD 5 and DOC removals of 53.7, 36.7 and 44.1%, respectively, color reduction of 89.3% and smaller decreases in total phosphorus and total nitrogen concentrations (29.7 and 2.7%, respectively). Chapter 11 – Cotton Dyeing Wastewater Treatment 270 #1 to #3). The COD, DOC and color removals reached in Fenton’s reaction are in all strategies higher than in the coagulation/flocculation stage, but BOD 5 shows an opposite behavior. As expected, much better treatment efficiencies are reached in run #3, where doses of chemicals in the Fenton’s stage are higher (69.2, 60.4, 72.4, and 96.6% for COD, BOD 5 , DOC and color, respectively). Final COD values below the discharge standards were only reached in runs#2 and #3, where greater H 2 O 2 (and Fe 2+ ) doses were used. However, despite the slightly lower organic matter removal efficiency, the chemical dosages used in run #2 were selected because they originate smaller operating costs (0.87 €/m 3 ), comparatively to run #3 (1.2 €/m 3 ), which is associated with the lower H 2 O 2 and Fe 2+ concentration employed, without compromising compliance with the legislated discharge standards. The use of dissolved iron resulting from Fenton process as coagulant in the subsequently stage of coagulation/flocculation represents an economic advantage, since the operating cost is reduced by 27.5% comparatively to Fenton’s oxidation alone. Part IV 271 Table 11.3 - Characteristics of the cotton dyeing wastewater after Fenton’s oxidation and coagulation/flocculation (Approach 3) and global removal for the combined process (runs #1 to #3 correspond to different dosages of hydrogen peroxide in the Fenton’s stage; percent removal efficiencies are given within brackets for each isolated process). Parameter Run #1 – 0.625 g H 2 O 2 /L Run #2 – 0.938 g H 2 O 2 /L Run #3 – 1.25 g H 2 O 2 /L Fenton’s oxidation Coagulation & flocculation Global removal (%) Fenton’s oxidation Coagulation & flocculation Global removal (%) Fenton’s oxidation Coagulation & flocculation Global removal (%) Discharge limit*** pH 1.20 7.0 - 1.25 7.02 - 1.10 7.03 - 5.5-9.0 Chemical oxygen demand (mg O 2 /L) 347.5 (29.8) 270.0 (22.3) 45.5 292.5 (40.9) 185.0 (36.8) 62.6 260.0 (47.5) 152.5 (41.3) 69.2 250 Biochemical oxygen demand (mg O 2 /L) 116.3 (8.8) 91.8 (21.1) 28.0 106.4 (16.5) 66.9 (37.1) 47.5 85.3 (33.1) 50.5 (40.8) 60.4 100 Dissolved organic carbon (mg C/L) 124.9 (28.5) 94.9 (24.0) 45.7 98.4 (43.7) 62.2 (36.8) 64.4 82.4 (52.8) 48.3 (41.4) 72.4 - BOD 5 :COD ratio 0.33 0.34 - 0.36 0.36 - 0.33 0.33 - - Absorbance at λ max (abs. units) 0.0407 (94.0*) 0.0234 (43.2**) 96.6 0.0392 (94.2*) 0.0230 (41.6**) 96.6 0.0387 (94.3*) 0.0233 (40.4**) 96.6 - Visible color after dilution 1:40 not visible not visible - not visible not visible - not visible not visible - not visible * calculated from the absorbance of wastewater at pH 3.5 (0.6805 abs. units). ** calculated from the absorbance after Fenton at pH 5.0 (0.0412, 0.0394 and 0.0391 abs. units for run #1, #2 and #3, respectively). *** Portuguese legislation for discharge of textile wastewaters (Ordinance No. 423/97 of 25 June). Chapter 11 – Cotton Dyeing Wastewater Treatment 272 11.4.5 Combination of Fenton´s Reaction and SBR (Approach 4) As the biodegradability of the raw wastewater (in terms of BOD 5 :COD ratio and k') slightly increased after Fenton’s oxidation (from 0.26 and 8.85 mg O 2 /(g vss h) to 0.36 and 9.5 mg O 2 /(g vss h), respectively), and there was also a reduction in Vibro fischeri inhibition, as shown in Tables 11.1 and 11.2, the alternative integrated process consisting of Fenton’s reaction followed by SBR was studied. Three experiments were performed using different doses of chemicals in Fenton’s oxidation stage. One experiment (run #3) was performed under the optimal conditions determined in Approach 2 (37.5 mg/L Fe 2+ and 1.25 g/L H 2 O 2 ); in the other runs the doses of H 2 O 2 and Fe 2+ were reduced to 3/4 and 1/2, respectively, with the objective of reducing the operating costs (runs #2 and #1, respectively) (see Figure 11.1). Figure 11.4 shows the COD, DOC, BOD 5 , color, total nitrogen and total phosphorus removals during 10 cycles of SBR operation for the 3 runs; one can conclude that the removals for all parameters analyzed remained practically constant after 6 cycles in all runs/strategies tested, which means that a pseudo-steady state was reached. The efficiencies increased with the doses of chemicals used in the Fenton’s reaction (run #3 > run #2 > run #1), simultaneously with a significant decay of toxicity and a slight increase of biodegradability (see also Table 11.4). Particularly the inhibition of Vibrio fischeri decreased from 44.5-49.2% in run # 1 to 0.0 (non-inhibition) in run # 3. The average removals achieved in the last 4 cycles are presented in Table 11.4. BOD 5 removal was greater in SBR probably due to the breakdown of the more recalcitrant compounds by chemical oxidation. As regards decolorization, about 94% of the absorbance of raw wastewater was removed by the Fenton’s reaction and only 38-40% of the residual absorbance was removed in the SBR. Part IV 273 Figure 11.4 - Variation of COD (a), DOC (b), BOD 5 (c), color (d) total nitrogen (e) and total phosphorus (f) removals along 10 cycles of SBR operation, after treatment by Fenton’s oxidation. Runs #3 to #1 refer to Fenton’s stage with progressively decreasing doses of chemicals. 0 20 40 60 80 100 0 1 2 3 4 5 6 7 8 9 10 COD removal (%) Number of Cycles Run # 1 Run # 2 Run # 3 a) 0 20 40 60 80 100 0 1 2 3 4 5 6 7 8 9 10 DOC removal (%) Number of Cycles Run # 1 Run # 2 Run # 3 b) 0 20 40 60 80 100 0 1 2 3 4 5 6 7 8 9 10 BOD 5 removal (%) Number of Cycles Run # 1 Run # 2 Run # 3 c) 0 20 40 60 80 100 0 1 2 3 4 5 6 7 8 9 10 Color removal (%) Number of Cycles Run # 1 Run # 2 Run # 3 d) 0 5 10 15 0 1 2 3 4 5 6 7 8 9 10 Total Nitrogen removal (%) Number of Cycles Run # 1 Run # 2 Run # 3 e) 0 5 10 15 20 0 1 2 3 4 5 6 7 8 9 10 Total Phosphorus removal (%) Number of Cycles Run # 1 Run # 2 Run # 3 f) Chapter 11 – Cotton Dyeing Wastewater Treatment 274 Table 11.4 – Characteristics of the cotton dyeing wastewater after Fenton´s reaction and SBR (Approach 4) and average (last four cycles for SBR) and global removals (respective removal efficiencies are given within brackets for each processes). Parameter Run #1 – 0.625 g H 2 O 2 /L Run #2 – 0.938 g H 2 O 2 /L Run #3 – 1.25 g H 2 O 2 /L Discharge limit*** Fenton SBR Global Removal (%) Fenton SBR Global Removal (%) Fenton SBR Global Removal (%) pH 7.12 7.17 --- 7.05 7.15 --- 7.09 7.17 --- 5.5-9.0 Total nitrogen (mg N/L) 1021.8 (4.0) 1005.4 (1.6) 5.5 1021.8 (4.0) 929.1 (9.1) 12.7 1021.8 (4.0) 905.5 (11.4) 14.9 Total phosphorus (mg P/L) 4.2 (1.2) 3.8 (8.4) 9.5 4.2 (1.7) 3.7 (10.4) 11.9 4.2 (1.2) 3.6 (13.3) 14.3 COD (mg O 2 /L) 346.5 (30.0) 281.8 (18.7) 43.1 294.1 (40.6) 183.3 (37.7) 63.0 232.8 (53.0) 79.2 (66.0) 84.0 250 BOD 5 (mg O 2 /L) 114.2 (10.4) 93.4 (18.2) 26.7 103.4 (18.9) 64.4 (37.7) 49.5 84.7 (32.6) 28.6 (66.2) 77.6 100 DOC (mg C/L) 124.7 (28.5) 103.3 (17.2) 40.8 98.0 (43.8) 61.7 (37.0) 64.6 82.5 (52.7) 28.1 (65.9) 83.9 SOUR – Specific oxygen uptake rate (k’) (mg O 2 /(g VSS .h)) 8.9 n.d. --- 9.1 n.d. --- 9.5 n.d. --- BOD 5 :COD ratio 0.33 0.33 --- 0.35 0.35 --- 0.36 0.36 --- Absorbance at λ max (a.u.) 0.0410 (94.0*) 0.0257 (38.1**) 96.3 0.0393 (94.2*) 0.0240 (39.5**) 96.5 0.0386 (94.3*) 0.0234 (40.0**) 96.6 Visible color after dilution 1:40 not visible not visible --- not visible not visible --- not visible not visible --- not visible Vibrio fischeri Inhibition 5 min (%) 44.5 n.d. --- 11.0 n.d. --- 0.0 n.d. --- Vibrio fischeri Inhibition 15 min (%) 46.7 n.d. --- 23.1 n.d. --- 0.0 n.d. --- Vibrio fischeri Inhibition 30 min (%) 49.2 n.d. --- 26.7 n.d. --- 0.0 n.d. --- n.d. – not determined. * calculated from the absorbance at 520 nm of raw wastewater at pH 3.5 (0.6805 abs. units). ** calculated from the absorbance at 520 nm of wastewater after Fenton at pH 7.0 ( 0.0415, 0.0397 and 0.0390 abs. units in run #1, #2 and #3, respectively). *** . Ordinance No. 423/97 of 25 June. Part IV 275 As shown in Figure 11.5, the operating costs associated with the consumption of chemicals and energy increase with the amount of chemicals used in the chemical treatment, i.e, run #3 (2.4 €/m 3 ) > run #2 (2.1 €/m 3 ) > run #1 (1.8 €/m 3 ). However, only runs #2 and #3 allowed obtaining effluents that meet the discharge standards, namely in terms of COD (see Table 4). As the costs are slightly smaller, conditions used in run #2 are proposed for practical applications. The overall efficiencies achieved by the combination of Fenton’s oxidation and biological degradation in SBR under such conditions are 63.0, 49.5, 64.6, 12.7, 11.9 and 96.5% for COD, BOD 5 , DOC, total nitrogen, total phosphorus and color, respectively. It is noteworthy that such integrated process is more expensive than Fenton’s oxidation per se (cf. Figure 11.5), which is due to energy consumption in the SBR, although doses of chemicals were minimized in the chemical oxidation stage. Figure 11.5 - Operating costs of Fenton alone and Fenton plus SBR for treatment of a real cotton dyeing wastewater. 11.5 Conclusions A combination of coagulation/flocculation and Fenton’s oxidation, Fenton’s oxidation alone, and integrated processes of Fenton´s oxidation with coagulation/flocculation or biological degradation in SBR was applied to a real cotton dyeing wastewater aiming at 0 1 2 3 Fenton Run #1 Run #2 Run #3 Operating Cost (€/m3) Fenton plus SBR Chapter 11 – Cotton Dyeing Wastewater Treatment 276 organic matter mineralization, color removal and toxicity reduction while obtaining an effluent that meets the legislated discharge limits at the lower operating cost. All the treatment processes tested allowed obtaining an effluent that comply with the discharge limits, but the cheapest alternatives are the application of coagulation/flocculation followed by Fenton’s oxidation or, inversely, the combination of Fenton’s oxidation with subsequent coagulation/flocculation process. The operating costs associated to the consumption of chemicals are 0.83 and 0.87 €/m 3 , respectively. This is in part explained by initially using a cheaper treatment that permits a reduction of the amounts of chemicals employed in the second process, then decreasing the total costs (Approach 1) and by taking advantage of dissolved iron resulting from Fenton’s reaction, as coagulant in the coagulation/flocculation step (Approach 3). Global removal efficiencies of 99.5, 70.8, 66.1, 47.6% and 96.6, 62.6, 64.4 and 47.5 % were obtained for color, COD, DOC and BOD 5 , respectively, in the first and second integrated treatment processes (Approaches 1 and 3). 11.6 References Alaton, I.A.; Teksoy, S. (2007). Acid Dyebath Effluent Pretreatment Using Fenton’s Reagent: Process Optimization, Reaction Kinetics and Effects on Acute Toxicity. Dyes Pigments, 73, 31-39. Azbar, N.; Yonar, T.; Kestioglu, K. (2004). Comparison of various advanced oxidation processes and chemical treatment methods for COD and color removal from a polyester and acetate fiber dyeing effluent. Chemosphere, 55, 35-43. Bali, U.; Karagözoglu, B. (2007). Performance comparison of Fenton process, ferric coagulation and H2O2/pyridine/Cu (II) system for decolourization os Remazol Turquoise Blue G-133. Dyes Pigments, 74, 73-80. Blanco, J.; Torrades, F.; Varga, M. de la; García-Montaño, J. (2012). Fenton and biological-Fenton coupled processes for textile wastewater treatament and reuse. Desalination, 286, 394-399. Elmolla, E.S.; Chaudhuri, M. (2012). The feasibility of using combined Fenton-SBR for antibiotic wastewater treatment. Desalination, 285, 14-21. Li, J.; Luan, Z.; Yu, L.; Ji, Z. (2012). Pretreatment of acrylic fiber manufacturing wastewater by the Fenton process. Desalination, 284, 62-65. Meriç, S.; Selçuk, H.; Belgiorno, V. (2005). Acute toxicity removal in textile finishing wastewater by Fenton’s oxidation, ozone and coagulation-flocculation processes. Water Research, 39 (6), 11471153. Part IV 277 Oller, I.; Malato, S.; Sánchez-Pérez, J.A. (2011). Combination of advanced oxidation process and biological treatments for wastewater decontamination – A review. Science of the Total Environmental, 409, 4141-4156. Papadopoulos, A.E.; Fatta, D.; Loizidou, M. (2007). Development and optimization of dark Fenton oxidation for treatment of textile wastewaers with high organic load. Journal of Hazardous Material, 146, 558-563. Perdigon-Melon, J.A.; Carbajo, J.B.; Petre, A.L.; Rosal, R.; Garcia-Calvo, E. (2010). CoagulationFenton coupled treatment for ecotoxicity reduction in highly polluted industrial wastewater. Journal of Hazardous Materials, 181, 127-132. Peres, J.A.; Heredia, J.B. de; Domínguez, J.R. (2004). Integrated Fenton’s reagent – coagulation/flocculation process for the treatment of cork processing wastewaters. Journal of Hazardous Materials, 107 (3), 15-121. Ramirez, J.H.; Costa, C.A.; Madeira, L.M. (2005). Experimental design to optimize the degradation of the synthetic dye orange II using Fenton’s reagent. Catalysis Today, 107-108, 68-76. Rodrigues, C.S.D.; Madeira, L.M.; Boaventura, R.A.R. (2009 a)). Treatment of textile effluent by chemical (Fenton’s Reagent) and biological (Sequencing batch reactor) oxidation. Journal of Hazardous Materials, 172, 1551-1559. Rodrigues, C.S.D.; Madeira, L.M.; Boaventura, R.A.R. (2009 b)). Optimization of the azo dye Procion Red H-EXL degradation by Fenton’s reagent using experimental design. Journal of Hazardous Materials, 164, 987-994. Sanchis, S.; Polo, A.M.; Tobaja, M.; Rodriguez, J.J.; Mohedano, A.F. (2013). Degradation of clorophenoxy herbicides by coupled Fenton and biological oxidation. Chemosphere, in press. DOI:10.1016/j.chemosphere.2013.04.097. Wu, D.-L.; Wang, W.; Guo, Q.-W.; Shen, Y.-H. (2013). Combined Fenton-SBR process for bamboo industry wastewater treatment. Chemical Engineering Journal, 214, 278-284. Wu, H.; Wang, S. (2012). Impacts of operating parameters on oxidation-reduction potential and pretreatment efficacy in the pretreatment of printing and dyeing wastewater by Fenton process. Journal of Hazardous Materials, 243, 86-94. Xing, Z.-P.; Sun, D.-Z. (2009). Treatment of antibiotic fermentation wastewater by combined polyferric sulfate coagulation, Fenton and sedimentation process. Journal of Hazardous Materials, 168, 1264-1268. Part V Conclusions and Suggestions for Future Work Chapter 12 – Concluding Remarks and Forthcoming Work 286 Table 12.1 – Treatment approaches tested, analysis of compliance with maximum allowable values and operating costs for each simulated effluent and real wastewater tested. In bold are highlighted the cheapest strategies for each effluent that complie with legal limits for discharge. Treatment Approach * Simulated Effluents Real Wastewater Acrylic Dyeing Cotton Dyeing Polyester Dyeing Cotton Dyeing Compliance with Discharge Standards ** Operating Cost (€/m 3 ) Compliance with Discharge Standards ** Operating Cost (€/m 3 ) Compliance with Discharge Standards ** Operating Cost (€/m 3 ) Compliance with Discharge Standards ** Operating Cost (€/m 3 ) C/F No 3.7 No 0.25 No 2.0 No 0.25 C/F + FR Yes 7.0 Yes 0.83 Yes 3.1 Yes 0.83 FR No 18.1 No 9.2 Yes 2.7 Yes 1.2 FR + C/F Yes 9.1 Yes 4.6 Yes 1.3 Yes 0.87 PhFR Yes 5.8 Yes 3.5 Yes 1.0 --- --- SBR --- --- No 1.2 No 1.2 --- --- FR + SBR Yes 14.8 Yes 5.8 Yes 2.6 Yes 2.1 * C/F – coagulation/flocculation; FR – Fenton’s reaction: PhFR – photo-Fenton’s reaction with solar radiation; SBR – sequencing batch reactor. ** According to Portuguese legislation – Ordinance No. 423/97 of 25 June. Part V 287 12.2 Forthcoming Work For future work it is suggested to study the possibility of recycling the iron sludge resulting from the Fenton process as catalyst in the same oxidation process or as coagulant, thus decreasing the treatment costs and avoiding the sludge deposition. Such approach could also be tested in reactors operating in continuous rather than discontinuous mode. When applying the combination of Fenton’s oxidation plus coagulation/flocculation or SBR it was possible to reduce the doses of chemicals in the oxidation stage while maintaining the compliance with the discharge limits. Such approach could also be tested in reactors operating in continuous rather than discontinuous mode. With respect to the biological process it wouldl be interesting to investigate the influence of the duration of each cycle and the duration of each phase of the cycle, as well as the effect of the temperature and other conditions on the efficiency of the biological degradation. The treatment of industrial textile dyeing wastewaters by the photo-Fenton process using natural sunlight instead of simulated sunlight should be further studied and optimized. The treatability study of the real cotton (and other) dyeing wastewater could include the optimization of each process or combination of processes, namely by using multivariate statistical tools. Given the high treatment efficiency resulting from the application of the integrated process of coagulation/flocculation followed by Fenton’s reaction and vice versa, and particularly to the real cotton dyeing wastewater, allowing obtaining an effluent that meets the discharge standards at low operating cost, the study should proceed in continuous mode operation for similar and other types of effluents. Finally, this study could be extended by applying the electro-Fenton or electro-photoFenton processes to real textile dyeing effluents. Appendix Supporting Information Appendix 291 A.1 Supporting Information for Chapter 4 This appendix shows the experimental results obtained in the evaluation of the effect of the stirring speed and time of coagulation (Figures A.1 and A.2) and flocculation (Figures A.3 and A.4) on the synthetic cotton and polyester wastewaters treatment by coagulation/flocculation using Fe 2+ as coagulant and Magnafloc 155 as flocculant. Figure A.1 – Influence of the stirring rate on the coagulation stage for DOC (a) and color (b) removal from polyester and cotton simulated effluents (t coagulation =3 min, T=T ambient =23-25 ºC, [Fe 2+ ]=200 mg/L and pH=8.3). Figure A.2 – Effect of the coagulation time on DOC (a) and color (b) removal from polyester and cotton simulated effluents (v coagulation =150 rpm, T=T ambient =22-24 ºC, [Fe 2+ ]=200 mg/L and pH=8.3). 0 10 20 30 40 50 60 100 150 200 DOC removal (%) v coagulation (rpm) Polyester Cotton a) 0 20 40 60 80 100 100 150 200 Color removal (%) v coagulation (rpm) Cotton b) 0 10 20 30 40 50 60 1 2 3 5 DOC removal (%) t coagulation (min) Polyester Cotton a) 0 20 40 60 80 100 1 2 3 5 Color removal (%) t coagulation (min) Cotton b) 292 Figure A.3 - Variation of DOC (a) and color (b) removal with the stirring speed in the flocculation stage for polyester and cotton simulated effluents (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =22-28 ºC, pH polyester =8.3, pH cotton =9.4, [Fe 2+ ] polyester =[Fe 2+ ] cotton =200 mg/L, t flocculation =15 min and [Magnafloc 155]=2.5 mg/L). Figure A.4 – Influence of the flocculation time on DOC (a) and color (b) removal from polyester and cotton simulated effluents (v coagulation =150 rpm, t coagulation =3 min, T=T ambient =22-28 ºC, pH polyester =8.3, pH cotton =9.4, [Fe 2+ ] polyester =[Fe 2+ ] cotton =200 mg/L, v flocculation =20 rpm and [Magnafloc 155]=2.5 mg/L). 0 10 20 30 40 50 60 20 30 50 DOC removal (%) v flocculation (rpm) Polyester Cotton a) 0 20 40 60 80 100 20 30 50 Color removal (%) v flocculation (rpm) Cotton b) 0 10 20 30 40 50 60 15 30 45 DOC removal (%) tflocculation (min) Polyester Cotton a) 0 20 40 60 80 100 15 30 45 Color removal (%) t flocculation (min) Cotton b) Appendix 293 A.2 Supporting Information for Chapter 9 Some experimental results obtained in the treatment of the simulated effluents by the photo-Fenton process are presented below. a) b) c) Figure A.5 – Effect of radiation intensity on DOC and color removal from the cotton effluent during the photo-Fenton process with artificial radiation for 3.75 g/L (a), 5 g/L (b) and 10 g/L (c) of hydrogen peroxide (T=50 ºC, Fe 2+ :H 2 O 2 =1:33 and pH=3.5). 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 253 W/m2 500 W/m2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 7 W/m2 107 W/m2 220 W/m2 253 W/m2 500 W/m2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 7 W/m2 107 W/m2 253 W/m2 500 W/m2 294 a) b) c) Figure A.6 – Effect of the radiation intensity on DOC removal from the polyester effluent during the photo-Fenton process for 0.938 g/L (a), 1.25 g/L (b) and 2.5 g/L (c) of hydrogen peroxide (T=50 ºC, Fe 2+ :H 2 O 2 =1:7 and pH=3.5). 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 253 W/m2 500 W/m2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 7 W/m2 107 W/m2 220 W/m2 253W/m2 500 W/m2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 7 W/m2 107 W/m2 253 W/m2 500 W/m2 Appendix 295 a) b) c) Figure A.7 – Effect of H 2 O 2 dose on DOC and color removal from the acrylic (a), cotton (b) and polyester (c) effluents using photo-Fenton’s oxidation with simulated sunlight (radiation intensity = 500 W/m 2 , T=50 ºC, Fe 2+ :H 2 O 2 acrylic =1:57, Fe 2+ :H 2 O 2 cotton =1:33 Fe 2+ :H 2 O 2 polyester =1:7, pH=3.5). 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 6.5 g/L H2O2 10 g/L H2O2 20 g/L H2O2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0 20 40 60 80 100 0 20 40 60 80 100 120 Color removal (%) Irradiation time (min) 3.75 g/L H2O2 5 g/L H2O2 10 g/L H2O2 0 20 40 60 80 100 0 20 40 60 80 100 120 DOC removal (%) Irradiation time (min) 0.938 g/L H2O2 1.25 g/L H2O2 2.5g/L H2O2