Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles

ABATEMENT OF CHLORINATED PESTICIDES (HEXACHLOROCYCLOHEXANES) BY ZERO VALENT IRON MICROPARTICLES JOANA MARIA PARCHÃO OLIVEIRA DISSERTAÇÃO DE MESTRADO APRESENTADA À FACULDADE DE ENGENHARIA DA UNIVERSIDADE DO PORTO EM ENGENHARIA QUÍMICA M 2016 Integrated Masters in Chemical Engineering Abatement of Chlorinated Pesticides (Hexachlorocyclohexanes) by Zero Valent Iron Microparticles Master Thesis of Joana Maria Parchão Oliveira Developed in the scope of the curricular unit Dissertation Accomplished in Universidad Complutense Madrid Orientation in UCM: Dr. Aurora Santos López Dr. Sergio Rodriguez Vega Department of Chemical Engineering July of 2016 Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Acknowledgments The realization of this thesis was performed in the INPROQUIMA group directed by Dr. Arturo Romero Salvador whom I thank for accepting me and for giving me the opportunity to work in such an academically supporting environment leading to an exciting experience abroad. I would like to express my sincere gratitude to my thesis coordinator Dr. Aurora Santos López who not only was also responsible for my acceptance at INPROQUIMA, but included me into the group and spared no means into all the material and support necessary. Thank you for all the support shown, concern, knowledge sharing and for providing guidance over this internship. I would like to thank my thesis coordinator Dr. Sergio Rodriguez Vega who was always ready to answer any question and facilitate their time to me whenever I needed to discuss something or needed help. I am particularly grateful for the assistance of Dr. Carmen Domínguez Torre for the tireless support she provided. I am very grateful for her partnership in the past few months and I would like to thank her for all the concern, good advice, patience and motivation. To all members of INPROQUIMA group and to my colleague, Eva, a huge thank you for all the help and companionship provided, creating a great work environment inside the laboratory. To all my professors and colleagues at FEUP who were responsible for bringing me to this point in my studies. I would like to particularly mention Prof. Luís Miguel Madeira who encourages students to seek an academic experience abroad. He was responsible for most of my mobility process, being always available to answer my questions and concerned with the evolution of the project. To all my friends who accompanied me along the last years and were always present when I needed to exchange ideas or talk about frustrations related to work. Thank you so much for all the support in my personal and academic life. Finally, for the unconditionally support emotionally and financially, thank you to my family, specially my mother who is always present in any decision I make and my grandparents, Irene and António Parchão, who have always guided me closely and motivated academically, regardless the barriers imposed by age. I can never repay you enough for everything you have done for me. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Abstract Nowadays, society is liable for the consequences associated with the excesses in the past. The treatment and management of contaminated sites arising from the uncontrolled and unregulated release of toxic waste is a matter of great global impact. Hexachlorocyclohexane was one of the mostly used pesticides since World War II until the 1990s. This compound, constituted by different isomers, is considered a persistent organic pollutant. Consequently, their treatment is now regulated upon detection in industrial waste and contaminated soil or water. Therefore, there are several research projects promoting its degradation, among which is highlighted the reductive dechlorination using zero valent iron microparticles. This dissertation was carried out to study the , ,  and hexachlorocyclohexane isomers dechlorination reaction using zero valent iron microparticles. Their reactivity order was defined, as well as the possible interference of four isomers coexisting in the same solution on its degradation. A stability test was carried out in order to determine whether these microparticles keep stable throughout its use, using the same iron particles in three consecutive reaction cycles, for each isomer separately. According to each isomer behaviour, -hexachlorocyclohexane was selected to study the influence of operating conditions in the dechlorination reaction. Thereby, it was elaborated an analysis of the initial pollutant concentration effect on the reaction (0.5, 3 and 6 mg/L), followed by the influence study of using different iron concentrations (1, 5 and 10 g/L). In addition, the temperature influence was analysed (10, 20 and 30 °C). Afterwards, it was determined a kinetic model based on the study of the operating conditions influence in order to better understand the - hexachlorocyclohexane degradation process. In an attempt to simulate a more realistic situation, a small study was developed based on the possible effect of the addition of anions (HCO3-, SO42and Cl-) and cations (Ca2+, Mg2+ and Na+) in the degradation of -hexachlorocyclohexane. As in reality this treatment implementation is performed in continuous mode, it was designed a column where reactions occurred, attaining a degradation degree of this compound similarly to when comparing with the results obtained in batch mode. In addition, the microparticles stability and the effect of coexistence of isomers were also tested. In general, the experiments have yielded consistent results in both operating modes, resulting in the presentation of an estimated dechlorination reaction pathway for - hexachlorocyclohexane. Keywords: Hexachlorocyclohexane, Dechlorination, Reduction, ZVI Microparticles Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles iv Figure 20: Effect of anions on the lindane dechlorination reaction in terms of X  -HCH and Cl-/Clmax at T=20 ºC, CFe=5 g/L and Clindane0 = 6 mg/L (R15, R24-R26 and R30-R35). ....................................... 32 Figure 21: Lindane concentration evaluation in terms of 1-X and Cl-/Clmax (T=20°C, Clindane0 = 6 mg/L and pH0=7) for Batch and Column (R15 and RC1). ................................................................. 34 Figure 22: Lindane degradation reaction in column (T=20°C, Clindane0 = 6 mg/L and pH0=7) for different W/Ql values during 10 days (RC2). ................................................................................... 35 Figure 23: Degradation of different concentrations of HCH isomers in Batch and Column in terms of Cl- /Clmax at 20 °C (R13, RC3 and RC4). ................................................................................. 36 Figure 24: Concentration evolution for different compounds involved in the dechlorination of lindane (T = 20 ºC, Clindane0 = 6 mg/L, CFe = 5 g/L and pH0 = 7) in column (RC1). ....................................... 37 Figure 25: Evolution for different compounds involved in the dechlorination of lindane (T = 20 ºC, Clindane0 = 6 mg/L, CFe = 5 g/L and pH0 = 7) in terms of X, Cl-/Clmax, B/Bmax (RC1). .......................... 37 Figure 26: Proposed reaction pathway for degradation of lindane in the presence of zero valent iron microparticles. ........................................................................................................... 38 List of Figures - Annex I Figure A I 1: Chromatogram obtained by GC -MS for all HCH isomers and calibration curves. ........... 47 Figure A I 2: Chlorides calibration curve. ........................................................................... 48 Figure A I 3: Calibration curve for low concentration of chlorides. ........................................... 48 Figure A I 4: Calibration curve for high concentration of chlorides. .......................................... 49 Figure A I 5: Benzene calibration curve. ............................................................................ 49 Figure A I 6: Calibration curve for low concentration of benzene. ............................................ 50 List of Figures – Annex II Figure A II 1: Degradation of 0.5 mg/L of  -HCH in terms of 1-X at different temperatures. ............ 51 Figure A II 2: Degradation of 0.5 mg/L of  -HCH in terms of 1-X for longer reaction time. .............. 52 Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles v List of Tables Table 1: Isomeric conformation and average composition of technical HCH. ..................................2 Table 2: Comparison between mZVI and nZVI. .......................................................................8 Table 3: Properties of Zero Valent Iron microparticles used in the project. ................................ 10 Table 4: Chemicals used during experimentation. ................................................................ 12 Table 5: Objective and experimental conditions of reaction runs carried out in batch mode............ 14 Table 6: Objective and experimental conditions of the reaction runs carried out in continuous mode 15 Table 7: Experimental conditions of reaction runs carried out in Batch in order to study the presence of different ions. ........................................................................................................ 29 Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles vi Notation and Glossary B Benzene C Concentration mg/L Eq Equation k Rate Constant h-1 nd Not Defined T Temperature °C t Time h w Rotation per minute rpm r Radius S Superficial Area X Conversion Greek Letters  alpha HCH isomer  beta HCH isomer Ø Diameter  Porosity  delta HCH isomer  gamma HCH isomer  Density Indexes 0 Initial value app Apparent f Final value max Maximum value possible to obtain p Pore Listo of Acronyms AOP Advanced Oxidation Process ARP Advanced Reduction Process ATSDR Agency for Toxic Substances and Disease Registry DNAPL Dense Non-Aqueous Phase Liquids EFSA European Food Safety Authority Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles vii EPA US Environmental Protection Agency FAO Food and Agriculture Organization GC-MS Gas Chromatography – Mass Spectrometry HCH Hexachlorocyclohexane HPLC High Performance Liquid Chromatography IC Ion Chromatography ISCO In Situ Chemical Oxidation ISCR In Situ Chemical Reduction ITRC Interstate Technology & Regulatory Council mZVI Micro-scale Zero Valent Iron particles MW Molecular Weight nZVI Nano-scale Zero Valent Iron Particles POP Persistent Organic Pollutant PRB Permeable Reactive Barrier SPME Solid Phase Micro Extraction TOS Time on Stream UV Ultraviolet Radiation UNEP United Nations Environment Programme WHO World Health Organization ZVI Zero Valent Iron Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Introduction 1 1 Introduction 1.1 Project’s motivation and relevance In our society, for a long time, it has been normal to resort to the use of pesticides to control insect pests. Ever since society began to develop industrially and scientifically this use has become a global environmental and human health concern, leading to the need for regulatory agencies to control the overuse of pesticides [1]. The Food and Agriculture Organization (FAO) defined pesticide as a substance or mixture of substances meant for preventing, destroying or controlling any pest [2]. It can be a chemical or biological agent and despite their benefits, there are a few drawbacks such as potential toxicity to humans and other species. The risk of a pesticide depends on two things: exposure and toxicity. The exposure relates to the amount that gets on the human/animal body, or the amount that is released into the environment and the toxicity is a measure of how poisonous it is [3]. In 2006 and 2007, the world used approximately 2.4 megatons of pesticides, with herbicides constituting the biggest part of the world pesticide use at 40%, followed by insecticides (17%) and fungicides (10%) [4]. Of all types of pesticides, insecticides are the ones with the largest potential to change the environment where they are introduced in. These are classified based on their structure and mode of action, being one of the most well-known types the organochlorines. These, as is implicit, consist in chlorinated hydrocarbons [5]. Hexachlorocyclohexanes (HCH) were one of the most extensively used organochlorine pesticides worldwide, produced mostly after the Second World War until the 1990s. This pesticide, has been used both as technical HCH (a mixture of all its isomers) or as Lindane (isomer -HCH) [6]. HCHs were first prepared by Michael Faraday in 1825 by adding chlorine to benzene in the presence of UV resulting in an isomeric mixture consisting of five major stable isomers [7]. Depending on the orientation of the chlorine atoms, whether being axial (a) or equatorial (e), these isomers are named α-, β-, γ-, δand ε−HCH. The average composition of technical HCH along with the conformation of the different isomers is presented in Table 1 [8]. Due to its different conformations, each isomer has slightly different physical and chemical properties, excluding solubility that is very low for all of them in water [9]. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Introduction 2 Table 1: Isomeric conformation and average composition of technical HCH. Isomer Conformation Percentage -HCH aaeeee 65 - 70 -HCH eeeeee 7 - 10 -HCH aeeeee 6 - 10 -HCH aeeaee 1 - 2 -HCH aaaeee 14 - 15 Of all the HCHs isomers, -HCH presents the highest insecticidal properties. Therefore, in the 1950s some companies began to isolate this active ingredient until they achieved a purity of 99% for commercial purposes, identifying it as Lindane [10]. The purification process of this isomer from the technical mixture evolves multiple steps thereby increasing its production cost. Either companies choose to use the concentrated -HCH or the technical HCH mixture, about 85% of the product obtained throughout the process represents other isomers without insecticide activity that can be considered as by-products of Lindane production [11]. Normally these by-products became hazardous waste, which is very concerning since for each tonne of Lindane produced it is generated about 8 – 12 tonnes of other isomers [6]. Is estimated that between 4 and 7 million tonnes of wastes of toxic, persistent and bioaccumulative residues (largely consisting of  and -HCH) have been produced and discarded around the globe during the 60 years of Lindane production. These residues tend to accumulate in both soils, contaminating plants and consequently entering the animal feed chain, and water. They also contaminate the air, which is a concerning aspect as it serves as means of transport for the contaminants from stockpiles of waste to other places [10]. The peak production of Lindane occurred in the 1960s and the early 1970s and, although its use had stopped in several European countries by the 1970s, the largest share of its use and production was within Europe (representing approximately 63% of the total global, Figure 1) [6]. Most nations have banned the use of this pesticide over the years, except India that continued producing it until 2010 under the pretext of using Lindane for pharmaceutical purposes to control malaria [11]. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Introduction 3 Figure 1: Estimate of the quantity of HCH isomers deposited or stored as waste in different countries, based on a questionnaire process [6]. Lindane and other isomers, especially the - and -HCH, have carcinogenic, persistent, bioaccumulative and endocrine disrupting properties [12, 13]. Due to this and to its excessive use over several years, Lindane has become a heavily studied substance and has been highlighted for regulatory intervention in the early 2000s, leading to a proposal to frame it and its major isomers in the Stockholm Convention Persistent Organic Pollutant (POPs) list [13]. In 2009 Lindane, - and -HCH were accepted in the 4th meeting of the Conference for inclusion in the Stockholm Convention POPs list [14, 15], creating a global obligation to find ways to control and eliminate these contaminants. 1.2 Presentation of the Institucion INPROQUIMA group is integrated in the Chemical Engineering Department of Universidad Complutense of Madrid and focuses its activities towards sustainable development research. The researching lines addressed by this group are related to industrial and environmental processes, in order to improve the quality of products, the energy balance, the process safety and environmental concerns. 1.3 Labor Contributions One of the group's researching line is the treatment of waters containing organic contaminants, and currently new strategies are being developed for the treatment of water contaminated by HCHs. The work in this thesis was inserted in the ongoing investigation, Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Introduction 4 helped in its progress and in the preparation of a scientific paper. The behaviour of the different isomers of this contaminant had been studied, as well as the stability of the iron particles preselected for the reaction. In addition, the experiments were updated from batch to column bringing the study to more realistic situations. It was also developed a kinetic model and estimated the reaction route. 1.4 Thesis Layout This thesis is divided into five distinct chapters beginning with this introductory chapter, where a general perspective of the motivation and research questions underlying this work are presented. It is presented the pesticide in study and is explained the importance of finding an effective procedure to eradicate it. The following chapter presents the state of the art, containing the fundamentals required to understand the methods most commonly used to treat this type of contaminant as well as its applications to real situations. The developed project is contextualized in the work carried out by the research group and the assumptions made that led to choosing the techniques and materials used are explained. The third part of this document presents the technical description in which the used reagents and materials are discriminated. All the procedures performed throughout the project and analytical methods applied are described. In Chapter 4 all results obtained, by applying the methods described in the previous chapter, are presented and discussed. Initially is approached the study of the dechlorination reaction of HCHs, followed by an analysis of the effect of changing some operating parameters. It is determined the kinetic model for the study conducted previously and then examined the effect of the presence of salts in solution. The conducted study is also applied to a fixed bed reaction column to approximate the existing conditions to real environments. Finally, based on the elaborated work it is estimated the route of HCHs degradation reaction. In the final chapter, the main conclusions, along with comments on the limitations of this work and suggestions for future work are presented. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles State of the Art 5 2 State of the Art 2.1 Water and Soil Treatments The composition of HCH isomers around the world is variable, however its higher concentrations were detected in the northern hemisphere as expected since the major producers of HCH are located there [16]. Although HCHs have been deposited in stockpiles, their relatively high volatility has led to global transport even into outlying locations such as the Artic. This explains why HCHs can be detected in all environmental compartments such as water, soil, air or animals, and why it is important to study ways to eradicate these contaminants from both water and soil (where they mostly tend to deposit) [10]. Wastewaters can be composed of a very diverse mixture of compounds, largely dependent on what type of industry is creating the waste stream. Its treatment should begin at the source, keeping the contaminant’s level to its minimum and avoiding the discharge of harsh chemicals to the environment. Regardless whatever treatment steps a wastewater undertakes, a significant amount of wastewater treatment systems will have as a final step the discharge of effluent to a soil absorption system [17]. This is the reason why is important to comprehend how both soil and water treatments work, since these contaminants used to be released without any treatment [6]. Generally, both soil and water treatment methods include technologies associated with physical, chemical, biological and thermal processes [18, 19]. Soil remediation is necessary to clean and preserve high quality standards of soil and water and embraces various processes intended to remove contaminants such as hydrocarbons, pesticides and volatiles of soil. This processes can be divided in four main types of techniques: i) bioremediation that uses aerobic or anaerobic bacteria to consume or abolish the contaminants [7, 11]; ii) thermal remediation that intends to evaporate impurities; iii) air injections projected to force organic vapours outwards the soil; iv) encapsulation of contaminants [19]. The purpose of wastewater treatments is to allow the release of human and industrial effluents on the natural environment without polluting it. Commonly these consist of a combination of processes, each one with different purposes. Firstly, the effluent goes through a preliminary treatment to separate the largest materials often found in raw wastewaters and then is exposed to a primary treatment, intended for the removal of other solid particles by sedimentation. Then the effluent goes to a secondary treatment where suspended solids and residual organics are removed by processes like activated sludge, biofilters, oxidation Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 12 Table 4: Chemicals used during experimentation. Substance Chemical Formula MW (g/mol) Purity (%) Supply Company Application Acetone C3H6O 58.1 99.8 SigmaAldrich HCHs’ solvent Acetonitrile CH3CN 41.1 99.9 Scharlau HPLC mobile phase Benzene C6H6 78.1 99.9 SigmaAldrich HPLC identification and calibration Calcium Sulfate CaSO4 136.1 >99.0 Riser Ions effect Cyclohexanone C6H10O 98.1 >99.0 SigmaAldrich Internal Standard  - HCH C6H6Cl6 291 99.9 Fluka Pollutant  - HCH C6H6Cl6 291 99.8 Fluka Pollutant  - HCH C6H6Cl6 291 98.5 Fluka Pollutant  - HCH C6H6Cl6 291 99.4 Fluka Pollutant mZVI Fe0 55.8 99.0 Höganäs Reducing Agent Magnesium Sulfate MgSO4·7H2O 246.5 >99.0 Probus Ions effect Sodium Bicarbonate NaHCO3 84.0 99.7 Panreac IC analysis, Ions effect Sodium Carbonate Na2CO3 106.0 99.8 Panreac IC analysis Sodium Chloride NaCl 58.4 99.0 SigmaAldrich IC analysis, Ions effect Sodium Sulfate Na2SO4 142.0 99.0 SigmaAldrich Ions effect Sulfuric Acid H2SO4 98.1 95.0 Fisher Chemical HPLC mobile phase Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 13 3.2 Experimental Procedure The experiments carried out during the project can be separated into two parts: reactions in discontinuous (batch) and continuous (column). 3.2.1 Batch Reactions The dechlorination experiments were performed following the experimental procedure described in Figure 4. For each reaction, several glass bottles (26 mL) containing 20 mL of synthetic wastewater were placed simultaneously on an orbital thermostatic bath at an equivalent stirring velocity of 100 rpm. In order to analyze the evolution of reaction, reactors were removed from the bath at specific times. The liquid phase extracted was separated from mZVI using a magnet – to attract the majority of the iron - and a syringe with a 0.45 m Nylon filter to ensure that there’s no iron in the water to be examined. Then samples were immediately analyzed in High Performance Liquid Chromatography (HPLC), Gas Chromatography – Mass Spectrometry (GC-MS) and Ion Chromatography (IC). Regarding the experiments involving the study of iron stability, iron microparticles were recovered by filtration using a conical flask with vacuum assistance and a cellulose nitrate membrane (Øp = 1.20 m). These microparticles were dried at 60 ˚C for approximately 24 h and then used again in a new reaction cycle. Figure 4: Scheme of the experimental procedure followed in batch experiments. In Table 5 are summarized the dechlorination reaction runs carried in batch experiments, as well as the operating conditions studied. 5watch Glass 6incubator 1 2 3 4 5 6 1thermostatic bath 2syringe and filter 3sample containers 4conical flask Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 14 Table 5: Objective and experimental conditions of reaction runs carried out in batch mode. 3.2.2 Fixed Bed Column Reactions The dechlorination experiments in continuous mode were carried out using the experimental system represented on Figure 5. The “home-made” column was designed in order to present the same characteristics existing in batch reactions, such as the amount of Fe used (5 g/L) and the samples’ extracting method. This column consists of a Teflon pipe of Objective Reaction C (mg/L) C (mg/L) C (mg/L) C (mg/L) CFe (mg/L) Use of Fe T (˚C) HCH’s dechlorination reaction R1 0.5 - - - 5 1º 20 R2 0.5 - - - 2º R3 0.5 - - - 3º R4 - 0.5 - - 5 1º 20 R5 - 0.5 - - 2º R6 - 0.5 - - 3º R7 - - 0.5 - 5 1º 20 R8 - - 0.5 - 2º R9 - - 0.5 - 3º R10 - - - 0.5 5 1º 20 R11 - - - 0.5 2º R12 - - - 0.5 3º Dechlorination study, isomer's behaviour R13 0.5 0.5 0.5 0.5 5 1º 20 Influence of wastewater composition R1 0.5 - - - 5 1º 20 R14 3 - - - R15 6 - - - Temperature effect R16 6 - - - 5 1º 10 R15 6 - - - 20 R17 6 - - - 30 Iron concentration effect R18 6 - - - 1 1º 20 R15 6 - - - 5 R19 6 - - - 10 Ions presence effect R20-R38* 6 - - - 5 1º 20 * Described in detail in Table 7 of Section 4.4. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 15 10 cm length and 0.2 cm diameter. With the aim of supporting the iron microparticles, glass wool was placed below and above the fixed bed. Moreover, filters consisting on a combination of nylon between metallic mesh were placed between pipes connections and before the peristaltic pump. The solution containing HCH isomers was conducted upwards through the column by action of a peristaltic pump and directed to the waste container or to a needle for sampling, using a three-way valve. Figure 5: Scheme of the experimental procedure used in column experiments. The studied variables in column reactions are presented in Table 6 containing details of each performed reaction. Table 6: Objective and experimental conditions of the reaction runs carried out in continuous mode Objective Reaction C (mg/L) C (mg/L) C (mg/L) C (mg/L) W/QL (g*h/L) Comparison Batch / Column RC1 6 - - - 10 - 2778 Stability RC2 6 - - - 167 and 2778 HCHs mixture behaviour RC3 10 3 1.5 10 14 - 2778 HCHs mixture behaviour RC4 5 1.5 0.5 5 42 - 2778 2 1 3 4 5 6 7 8 9 10 4 11 12 7residue container 8needle 9sample containers 4glass wool 5mZVI 6three-way valve 1wastwater container 2peristaltic pump 3stand 10platform 11metallic mesh 12nylon filter Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 16 3.3 Analytical Methods The progress of the dechlorination reactions was studied analysing liquid samples at different reaction times. To evaluate the efficiency of the process four analytical techniques were used. 3.3.1 Gas Chromatography – Mass Spectrometry (GC-MS) To identify and quantify the HCH isomers over reaction time, a HP6890 Gas Chromatograph coupled with a HP5973 Mass Spectrometric Detector using a CTC CombyPAL (GC samples 80) was used. The extraction of the organic compounds was performed by solid phase microextraction (SPME) using polyacrylate coating fiber. The method used for this extraction had been previously optimized and consists in 3600 s at 38 ºC followed by the desorption process conducted in the injector at 270 ºC in splitless mode for 180 s. The separation of all compounds takes place on a SPB-624 fused-silica-capillary column (30 m x 0.25 mm ID and 1.40 µm thickness). Helium was used as carrier gas in a constant flow-rate of 1 mL/min. For each analysis the GC column was maintained at 45 ºC for 10 minutes, ramped at a rate of 12 ºC/min until 190 ºC and held at this temperature for 4 minutes. After this, a second ramp starts with a 3 ºC/min rate until it attains a temperature of 240 ºC which is then retained for 20min. The process ends with a post run of 240 ºC during 10 minutes. In all experiments 4-methylcyclohexanone was used as an internal standard (ISTD) with the aim of minimizing experimental errors. The calibration curves used to quantify HCH concentration are displayed in Anex I. All samples corresponding to the dechlorination reaction’s ending were measured in duplicate to confirm the results. This confirmation was achieved by comparing the chromatographic areas obtained with the ISTD areas. 3.3.2 Ion Chromatography (IC) The dechlorination degree was determined in based on the amount of chlorine ions released to the liquid phase. In order to quantify these ions, it was used an IC (Metrohm 761 Compact IC) with anionic chemical suppression using a conductivity detector. As stationary phase a Metrosep ASUPP5 column (5 cm length x 4 mm diameter) was used and as mobile phase, an aqueous solution of 3.2 mM Na2CO3 along with 1 mM of NaHCO3 flowing at 1 mL/min. To quantify chlorine concentration some calibrations were made as described in Anex I. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 17 3.3.3 High Performance Liquid Chromatography (HPLC) Benzene was identified and quantified by HPLC (Agilend, model 1100) with an Agilent poroshell 120 SB-C18 column as the stationary phase. The method used consisted on a mobile phase composed by a mixture of 4 mM H2SO4 aqueous solution and acetonitrile with a 40 and 60% ration, respectively, at a 0.5 mL/min flow. The analysis was performed with a diode array detector (G1315A) at a 210 nm wavelength. From each sample were extracted 20 µL which were then placed on the column which was maintained at 20 ºC and 84,6 bar for the 30 min needed to obtain the spectrum and chromatogram. The calibration curve used to quantify the benzene’s concentration is described in Anex I. 3.3.4 pH To ensure that the pH of each sample was maintained as intended and to observe if there were variations along with the reaction’s time these measurements were performed using a Basic 20-CRISON pH electrode. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 18 4 Results and Discussion 4.1 HCH’s dechlorination reaction 4.1.1 Reactivity of HCH isomers Solutions containing 0.5 mg/L of each HCH isomer were treated in discontinuous mode at room temperature and for a mZVI concentration of 5 g/L. The results obtained at 72 h reaction time, in terms of HCH conversion, are shown in Figure 6. The reactivity order found for HCHs isomers were γ-HCH > α-HCH > δHCH > β-HCH, which is consistent with the expected attending to their chlorines position. Isomers with the largest ratio of axial to equatorial chlorines are expected to be more reactive towards iron microparticles dechlorination. Thus, obtaining a variation range from 93 % for γ-HCH to less than 50 % regarding to -HCH. Figure 6: Reactivity order for HCHs isomers at 72 h reaction time (T=20°C, CFe= 5 g/L, CHCH0= 0.5 mg/L, pH0=7; R1, R4, R7 and R10). As previously seen, -HCH shows the most refractory behaviour. Besides that, due to the presence of all chlorine atoms in equatorial position (showed in Table 1 of Section 1.1) this isomer presents a reduced susceptibility to bio-chemical transformation [11] leading to a high bioaccumulation. Hence, some strategies were tested for its improvement. It was found that an increase temperature reaction from 20 to 30ºC did not lead to a significantly higher conversion. However, an increase in reaction time was more effective. A depletion of 85% of -HCH was achieved at 312 h reaction time, working at room temperature. It is observed an increase of 38 % in -HCH conversion comparatively with the 0 0.2 0.4 0.6 0.8 1     X HCH Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 19 one obtained for 96 h of reaction previously performed. All the graphs presenting the obtained results in both attempts, in terms of 1-X-HCH, can be found in Annex II. 4.1.2 Iron Microparticles Stability An extremely important aspect both for the economy and the applicability of this technology is the stability of the iron microparticles. It is intended that iron microparticles maintain the activity over a long period of time to be able to implement in the soil and ensure that they continue to react with the pollutant, in a stable manner. In order to determine whether these microparticles keep stable throughout its use, three consecutive reaction cycles were performed for the treatment of each isomer, separately. After the first use, iron microparticles were recovered as previously explained in Section 3.2.1 and then used again in the next reaction without further treatment. The stability results are presented in Figure 7. Figure 7: Degradation of HCH isomers in three successive runs (T=20°, CFe= 5 g/L CHCH0= 0.5 mg/L, pH0=7; R1-R12). 0.0 0.2 0.4 0.6 0.8 1.0 050 100 1-X -HCH Time (h) Use 1 Use 2 Use 3 a) 0.0 0.2 0.4 0.6 0.8 1.0 050 100 1-X -HCH Time (h) Use 1 Use 2 Use 3 b) 0.0 0.2 0.4 0.6 0.8 1.0 050 100 1-X -HCH Time (h) Use 1 Use 2 Use 3 d) 0.0 0.2 0.4 0.6 0.8 1.0 050 100 1-X -HCH Time (h) Use 1 Use 2 Use 3 c) Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 20 It is observed that the reactivity of iron microparticles, in the degradation of all isomers, is maintained in the three cycles tested. This is a great result, since it presents an important advantage over the nanoparticles, currently presented as a better approach to this subject. Although microparticles activity is lower, they can reach the same results with a longer reaction time and have greater durability. Furthermore, microparticles do not require pre-treatments to their use or possess a protective layer that may initially obstruct the contact between the reactive, unlike nanoparticles [54]. 4.1.3 Influence of wastewater composition The HCH isomers are not truly isolated, in reality these four isomers are mixed. Furthermore, with the goal of being more realistic, a solution containing the four isomers (0.5 mg/L of each) was treated with mZVI. The results, compared to those obtained for the isolated isomers, are presented in Figure 8. It was observed that all isomers in the presence of mZVI behave in the same way, either in the mixture or isolated, maintaining the reactivity order previously shown (Figure 6 of Section 4.1.1). However, the final conversion in the mixture for each isomer is slightly higher than when they are isolated. This fact can be related to a possible instability of the iron surface, for short reaction times, that goes unnoticed when a bigger concentration of pollutant is used (2 mg/L in the mixture vs 0.5 mg/L when isolated). Therefore, the presence of the other isomers doesn’t interfere with the degradation of each one, which is an interesting point since it is a more realistic approach. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 27 Figure 14: Apparent kinetic constants for different Temperatures with constant CFe and Clindane0 (reactions R15-R17). Using the obtained rate constants and considering Equation 6, the activation energy and pre-exponential factor were determined converting Equation 10 to its linear form, resulting in Equation 11. Then, the fitting of Ln(k) versus 1/T yields a straight line throughout the temperature range (R2 = 1), as shown in Figure 15. ln(𝑘)= −𝐸𝑎 𝑅𝑇 +ln(𝐴) Eq.11 Figure 15: Representation of Arrhenius Plot. The slope of the straight line gives an Ea of 55.44 kJ/mol, and the pre-exponential factor was calculated as 6.17x107 from the intercept of the line. Based on the results attained, the rate equation can be expressed as shown in Equation 12 by replacing the parameters determined and the values of each reaction. y = -0.0147x - 0.0392 R² = 0.9927 y = -0.0332x - 0.0252 R² = 0.9986 y = -0.0705x - 0.0742 R² = 0.9942 -6 -5 -4 -3 -2 -1 0 020 40 60 80 100 Ln(CLindane/CLindane0) Time (h) T = 10 ˚C T = 20 ˚C T = 30 ˚C y = -6729x + 17.937 R² = 1 -7 -6 -5 -4 -3 -2 -1 0 0.0032 0.0033 0.0034 0.0035 0.0036 Ln(k) 1/T (K-1) Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 28 −𝑟𝑙𝑖𝑛𝑑𝑎𝑛𝑒 = 6.17 ×107∙ 𝑒−55.44 𝑅·𝑇 · 𝐶𝐹𝑒 · 𝐶𝑙𝑖𝑛𝑑𝑎𝑛𝑒 Eq.12 This expression shows the dependence of the lindane dechlorination rate (mg/L·h) on t reaction temperature, mZVI concentration and initial lindane concentration. Furthermore, it allows the prediction of lindane reduction under different conditions, which is presented in Figure 16 with a comparison between experimental and simulated data characterized by an acceptable deviation (R2=0.989). Figure 16: Comparison between the data predicted by the model and the measured data for lindane concentration at the different operation conditions tested. 4.4 Effects of different ions on lindane degradation Common anions and cations normally present in soil and water/groundwater might affect the dechlorination reaction of HCHs. In this regard, it is an important subject of study when planning to apply these technologies in real situations. In order to comprehend the influence of different ions (and their concentration) in the degradation of -HCH, some reactions were performed. For this purpose, an initial -HCH concentration of 6 mg/L and mZVI dose of 5 g/L were selected. Additionally, the concentration range for each salt was selected based on the typical values founded in this type of contaminated waters. All reactions were carried out at room temperature and the final reaction time elected was 48 h, corresponding to a conversion of around 76 %. These reactions are described in Table 7. 0 1 2 3 4 5 6 0123456 Clindane, simulated (mg/L) Clindane, measured (mg/L) Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 29 Table 7: Experimental conditions of reaction runs carried out in Batch in order to study the presence of different ions. Objective Reaction Salt CSalt (mM) Anions effect 20 NaHCO3 2.0 21 10.0 22 20.0 24 Na2SO4 0.1 25 0.5 26 2.0 27 NaCl 5.0 28 15.0 29 50.0 Cations effect 30 CaSO4 1.0 31 5.0 32 10.0 33 MgSO4 0.1 34 1.0 35 5.0 24 Na2SO4 0.1 25 0.5 26 2.0 A very important factor to take into account during these reactions is the value of pH, which had been around neutral values and kept stable in reactions when no additional components were added to the reaction’s medium. In addition HCH dechlorination reactions are favoured when the solution pH is between 4 and 7 [43]. When its value decreases to this minimum, the reaction efficiency increases because of a better solubility of Fe(II) and Fe(III). However, if it goes bellow that value an intensive corrosion of iron occurs due to extremely acidic conditions. At pH higher than 8, Fe(II) and Fe(III) formed in the mZVI surface and OH− ions in the alkaline solution can react and form precipitate iron oxides/hydroxides. These precipitates most likely will settle on the mZVI surface occupying the reactive sites blocking their access to HCHs, thus reducing its degradation [43]. Thereby, pH was measured before and after the dechlorination reaction in the presence of mZVI particles. These values have been compared with those obtained in a reaction performed without salts addition, as shown in Figure 17. As the pH value was preserved since the beginning of the dechlorination reaction until its end when no ions were added to the process, only one representing line was used in the graph of Figure 17. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 30 Figure 17: Effect of ions presence on initial and final pH in the lindane dechlorination reaction at T=20 ºC, CFe=5 g/L and Clindane0 = 6 mg/L (R15, R20-R38). No significant changes on the initial pH were observed comparatively with the reaction without ions addition, except for the bicarbonates presence. In this case, the pH of the solutions increased greatly. Hence, these reactions took place in alkaline solutions with a pH range from 8.7 to 9.2, depending on the concentration of sodium bicarbonate used. Analysing the pH evolution for the reaction it is possible to say that is maintained constant except for calcium, that greatly increases, and for sulphate and sodium which slightly increase. As already mentioned, from the beginning bicarbonates tend to increase the pH of the solution. However, no changes were observed along the reaction. 4.4.1 Effects of anions presence As described in Table 7, all anions were added in the form of sodium salts to maintain constant the possible influence of the cation. All reactions were performed in a 48 h reaction time, as so the conversion expected would be around 76%. The results presented in Figure 18, in terms of X-HCH and Cl-/Clmax, are compared with reference values from a reaction with the same synthetic water but without ions (R15). In order to unify the ion addition analysis, it has been stablished an error range of 0.03 in lindane conversion represented in all graphs. When the studied anion was Clit was not possible to measure chlorides since a high amount would saturate the IC column. Consequently, there is not a correspondent value for Cl-/Clmax in this reaction study. 4 5 6 7 8 9 10 pH pH initial with salt pH final with salt no salt addition Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 31 Figure 18: Effect of anions presence on the lindane dechlorinarion reaction in terms of X  - HCH and Cl-/Clmax at T=20 ºC, CFe=5 g/L and Clindane0 = 6 mg/L (R15, R20-R29). It is notable that the presence of different anions does not interfere significantly on lindane degradation and on the dechlorination’s degree achieved. Analysing Figure 18a, it seems that an addition of bicarbonates to the reaction medium enhances the dechlorination reaction. As a result, the degradation efficiency attained was nearly 100%. Correspondingly, it is also observed a proportional increase in -HCH degradation along with the formation of Clin solution. It is possible to conclude that the reaction pathway is conserved regarding the addition of this salt and the results obtained were the same independently the amount of salt added. When sodium sulphate is added (Figure 18b) is possible to observe a slightly decrease for a high salt concentration. However, this variation is not significant in terms of lindane conversion. Regarding to chloride formation, the data does not show a clear tendency as the obtained differences were associated possible measurement errors. 0.0 0.5 1.0 HCO32mM HCO310mM HCO320mM X -HCH, Cl-/Clmax X Cl-/Clmax X no salts Cl/Clmax no salts 0.0 0.5 1.0 SO4 20.1 mM SO4 20.5 mM SO4 22 mM X -HCH, Cl-/Clmax X Cl-/Clmax X no salts Cl/Clmax no salts 0.0 0.5 1.0 Cl5mM Cl15mM Cl50mM X -HCH X X no salts a) b) c) Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 32 As shown in Figure 18c, the presence of chloride ions is associated with an increase in the conversion of -HCH. This increase seems to be independent of the salt concentration as the conversion obtained was similar regardless the concentration of salt. This minor variation is certainly related with the GC-MS sensitivity measurements since it had been reported by others that the addition of chloride is associated with an improvement in dechlorination reactions [55]. 4.4.2 Effects of cations presence In order to study the influence of cations presence in the lindane dechlorination reaction, different cations were added in the form of sulphate salts. The experiments were performed under the same conditions as was previously described for studying the anions presence effect (Section 4.1.4). The attained results are shown in Figure 19. Figure 19: Effect of anions on the lindane dechlorination reaction in terms of X  -HCH and Cl- /Clmax at T=20 ºC, CFe=5 g/L and Clindane0 = 6 mg/L (R15, R24-R26 and R30-R35). In the presence of magnesium sulphate is outstanding the difference between the conversion of -HCH and the formation of Cl-, noticeable in Figure 19a. The -HCH conversion seems to be increased by the addition of magnesium ions however the degree of 0.0 0.5 1.0 Mg 2+ 0.1mM Mg 2+ 1mM Mg 2+ 5mM X -HCH, Cl-/Clmax X Cl-/Clmax X no salts Cl/Clmax no salts 0.0 0.5 1.0 Ca 2+ 1mM Ca 2+ 5mM Ca 2+ 10mM X -HCH, Cl-/Clmax X Cl/Clmax X no salts Cl/Clmax no salts 0.0 0.5 1.0 Na 2+ 0.1 mM Na 2+ 0.5 mM Na 2+ 2 mM X -HCH, Cl-/Clmax X Cl-/Clmax X no salts Cl/Clmax no salts a) b) c) Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 33 dechlorination attained is much lower than expected. This could be explained by a possible precipitation of -HCH, which solubility is already low in pure water [56]. Additionally, could as well occur the precipitation of intermediate chlorinated compounds or chlorides formed. Moreover, the addition of calcium in the solution led to a slight increase in the -HCH conversion, as shown in Figure 19b. This increase seems to become more significant as the amount of CaSO4 used increases and it is followed by a rise in the concentration of chloride in solution, as expected. Concerning the sodium addition (Figure 19c), as it was tested with sulphate, it has already been commented in Section 4.4.1. 4.5 Application to Fixed Bed Reaction Column The implementation of HCH reduction by mZVI on a real situation (in situ treatment) would be performed in a similar way to reactive barriers, inserting these microparticles into the soil. Then, to bring the study to a more realistic situation, the experiments of HCH dechlorination were carried out using a tubular reactor (column). 4.5.1 Comparison between Batch and Column: Lindane degradation In order to understand whether the column works properly, it was initially tested a reaction with the same operation conditions as the R15 Batch reaction. This way it is possible to compare the results in continuous and discontinuous mode, both using 6 mg/L of -HCH. The previously Equation 5 presented in Section 4.3, which represents the mass balance for a discontinuous reactor, can be manipulated into Equation 13. The mass balance for a continuous reactor is demonstrated in Equation 14. In this equation the amount of Fe0 used is normalized by the flow that goes through the column, by increasing or decreasing the contact time of the effluent with the mZVI. −𝑑𝐶𝑙𝑖𝑛𝑑𝑎𝑛𝑒 𝐶𝐹𝑒𝑑𝑡 = 𝑘 × 𝐶𝑙𝑖𝑛𝑑𝑎𝑛𝑒 Eq.13 −𝑑𝐶𝑙𝑖𝑛𝑑𝑎𝑛𝑒 𝑑(𝑊 𝑄𝑙 ⁄)= 𝑘 × 𝐶𝑙𝑖𝑛𝑑𝑎𝑛𝑒 Eq.14 Moreover, associating these two expressions yields the relation expressed in Equation 15. This expression represents a means to compare results obtained in continuous with results from discontinuous mode. 𝐶𝐹𝑒 𝑑𝑡 = 𝑑 𝑊 𝑄𝑙 ⁄ ↔ 𝐶𝐹𝑒 × 𝑡 = 𝑊 𝑄𝑙 ⁄ Eq.15 Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 34 Afterwards, knowing that in batch mode were used 5 g/L of mZVI and the maximum reaction time was 96 h, the value of Ql was estimated to be 0.17 ml/min. With this value it is possible to attain total conversion using the same quantity of reducing agent. After the column bed stabilization, a solution of 6 mg/L of lindane was treated at different values of W/Ql, and the results are presented in Figure 20. Figure 20: Lindane concentration evaluation in terms of 1-X and Cl-/Clmax (T=20°C, Clindane0 = 6 mg/L and pH0=7) for Batch and Column (R15 and RC1). It can be noted that total conversion of lindane was obtained for shorter values of W/Ql in column reactions, similarly to the chloride formation. This fact can be related to a better contact between the lindane solution and the microparticles. Even so, in both ways total conversion is attained and the resulting profile follows the same tendency. Subsequently, is verified that the results obtained batchwise can be extrapolated to a continuous mode. 4.5.2 Long-term Stability Study A very important aspect for the economy of these processes is the stability of iron microparticles with reaction time. In order to attest the mZVI stability, long-term experiments were performed in continuous mode with a time on stream of 10 days. For this purpose, two values of W/Ql were selected. The lowest value corresponding to a flow of 0.5 ml/min (W/Ql of 167 g*h/L) and the higher one to 0.05 ml/min (W/Ql of 2778 g*h/L). The subsequent results are presented in Figure 21 where is notable that lindane conversion remains constant during 10 days of reaction. Accordingly, it is concluded that mZVI show a high stability. 0.0 0.2 0.4 0.6 0.8 1.0 0 200 400 600 800 1000 1-X-HCH, Cl-/Clmax CFe*t, W/Ql (g*h/L) 1-X HCH Batch Cl/Clmax Batch 1-X HCH Column Cl/Clmax Column Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 35 Figure 21: Lindane degradation reaction in column (T=20°C, Clindane0 = 6 mg/L and pH0=7) for different W/Ql values during 10 days (RC2). 4.5.3 Mixture of , , ,  – HCH isomers in Column In order to know if the dechlorination results obtained for lindane in continuous experiments also can be extrapolated to the rest of HCH isomers and to approximate the study to real operation conditions, synthetic wastewaters containing the four isomers were treated. Therefore, solutions with different concentration of HCH isomers were prepared depending on its water solubility as described in Table 5 of Section 3.2.2. The experiments were performed in a fixed-bed reactor column for a W/Ql range between 14-2778 g*h/L, correspondent to 6 and 0.03 ml/min, respectively. Additionally, the results for this two experiments were compared with reaction R13 performed in batch (initial solution with 0.5 mg/L of each isomer), as showed in Figure 22. Notably, the chloride mass balance was not closed for these reactions. Regarding the mixtures that reacted in column, it was not expected achieving total Cl-/Clmax, since for these concentrations it is not possible to attain total conversion of HCH for the W/Ql used. Nevertheless, the main reason for this low degradation degree is associated with the refractoriness of some HCH isomers, mostly -HCH as mentioned in Section 4.1.1. 0 0.2 0.4 0.6 0.8 1 0246810 X-HCH TOS (days) W/Ql=167 g*h/L W/Ql=2778 g*h/L Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Results and Discussion 36 Figure 22: Degradation of different concentrations of HCH isomers in Batch and Column in terms of Cl-/Clmax at 20 °C (R13, RC3 and RC4). 4.6 Reaction Pathway It is known that Lindane degradation can occur by dechlorination (loss of 2 Clowing to the electron exchange between HCH molecule and zero-valent iron) or dehydrohalogenation (loss of HCl) [27, 29]. After analysing all reactions performed during the experiments, a reaction with 6 mg/L of -HCH (RC1) was elected to study the reaction pathway. In Figure 23, it is possible to observe the evolution of concentration of the different species identified and quantified during lindane dechlorination experiments. It is notable that lindane abatement is accompanied by an increase in concentration of Cland benzene. Moreover, 3,4,5,6-Tetrachlorocyclohexene was detected in trace amounts by GC-MS, for short reaction times. However, it was not possible to quantify this intermediate due to its high instability [57]. 0.0 0.2 0.4 0.6 0.8 1.0 0 1000 2000 3000 Cl-/Clmax CFe*t, W/Ql (g*h/L) 12 mg/L Column 24 mg/L Column 2 mg/L Batch Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles References 42 References 1. Unsworth, J. (2010). History of Pesticide Use. Retrieved 21/04/2016, from http://agrochemicals.iupac.org/index.php?option=com_sobi2&sobi2Task=sobi2Details &catid=3&sobi2Id=31. 2. WHO and FAO, The International Code of Conduct on Pesticide Management. 2014. 3. 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Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles References 45 57. Chang, C., F. Lian, and L. Zhu, Simultaneous adsorption and degradation of γ-HCH by nZVI/Cu bimetallic nanoparticles with activated carbon support. Environmental Pollution, 2011. 159(10): p. 2507-2514. 58. ATSDR (2011). Toxic Substances Portal. Retrieved 25/06/2016, from http://www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=14. Annex I. Calibrations 46 Annex I. Calibrations In the course of the experimental work accomplished three calibrations were necessary to obtain the results shown previously. The results showed concerning the efficiency of the dechlorination process by degradation of HCH, release of chlorines and the formation of benzene were correlated with the integration area of the peaks obtain from GC-MS, IC and HPLC, respectively. The eligible characteristics for a good peak are clear separation between the different peaks, absence of tails and some narrowness. An ideal analysis comprehends these features and an accurate calibration curve correlating areas with concentrations in order to optimize the results. Therefore, were tested different calibration curves and selected those with the higher R2 for each analysis. The treatment of results was executed measuring the areas of each peak available on the analysis software and writing them in an excel sheet. Following are the results of the calibrations used to analyse the experimental results and the respective concentration window that they can be used with desirable and trustworthy results. HCHs The calibration method used to identify different HCH’s isomers had been prepared previously and applied to the data processing program. The calibration curves associated with each isomer are presented in Figure A I 1 along with the specific peaks for each one. The chromatogram present in this image compares reaction R1 at time zero and at the end (96h). It is easy to observe the decrease on the concentration of each isomer and the difference in the efficiency of their removal. Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Annex I Calibrations 47 Figure A I 1: Chromatogram obtained by GC -MS for all HCH isomers and calibration curves. Chloride A main solution with 1 g/L concentration in a 500 mL volumetric flask was prepared to obtain samples with different concentrations of chloride ions. A determined amount of NaCl was dissolved in ultrapure water considering a purity of 99.0% and that chlorine has a molar mass of 35 g/mol. From this solution, a designated volume was taken to attain a new solution with 20 mg/L concentration from which three other solutions were prepared in order to obtain 10, 5 and 1 mg/L. The curve obtained is showed in Figure A I 2 and it’s easy to understand that a linear regression should be drawn separately for low and high concentrations. Then, as showed in Figure A I 3 and Figure A I 4 linear regressions were obtained, one for concentrations under 2.5 mg/L and another for higher ones. -HCH y = 30.3390 x – 0.087 R2 = 0.995 -HCH y = 32.9817 x – 0.011 R2 = 0.982 -HCH y = 33.6865 x – 0.062 R2 = 0.999 -HCH y = 6.4849 x – 0.053 R2 = 0.991 Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Annex I Calibrations 48 Figure A I 2: Chlorides calibration curve. Figure A I 3: Calibration curve for low concentration of chlorides. y = 0.0073x + 0.4307 R² = 0.9954 0 5 10 15 20 25 0 1000 2000 3000 CChloride (mg/L) Area (µS/cm.sec) y = 0.0101x + 0.0275 R² = 0.9993 0.0 0.1 0.1 0.2 0.2 0.3 0 100 200 300 CChloride (mg/L) Area (µS/cm.sec) Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Annex I Calibrations 49 Figure A I 4: Calibration curve for high concentration of chlorides. Benzene A 1 L solution with a 100 mg/L concentration was prepared knowing that benzene has a molar mass of 78 g/mol and a density of 876,5 g/L. From this main solution designated volumes were taken in order to obtain 10, 5, 2.5, 1, 0.5, 0.25 mg/L. As showed in Figure A I 5 and Figure A I 6, the polynomial curve has a better R2 but the range of concentrations used to analyse the results includes the lowest concentrations. Therefore, a new linear regression focused on low concentrations was estimated in Figure I 6, defining an intercept on the origin. Figure A I 5: Benzene calibration curve. y = 0.007x + 1.1422 R² = 0.998 0.0 0.5 1.0 1.5 2.0 2.5 0 1000 2000 3000 CChloride (mg/L) Area (µS/cm.sec) y = 2E-07x2+ 0.0005x + 0.2976 R² = 1 0 20 40 60 80 100 0 10000 20000 30000 CBenzene (mg/L) Area (mUA) Abatement of Chlorinated Pesticides (Hexachlorocyclohexane) by Zero Valent Iron Microparticles Annex I Calibrations 50 Figure A I 6: Calibration curve for low concentration of benzene. y = 0.0011x R² = 0.9865 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0 500 1000 CBenzene (mg/L) Area (mUA)