Towards Sustainable Solid Waste Management in Nigeria: Integrating Analytic Hierarchy Process and System Dynamics for Policy and Practice

387 Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 p ISSN: 2635-3342; e ISSN: 2635-3350 Original Research Article Towards Sustainable Solid Waste Management in Nigeria: Integrating Analytic Hierarchy Process and System Dynamics for Policy and Practice *Oluwanimifise, M.K. and Anyaeche, C.O. Department of Industrial and Production Engineering, Faculty of Technology, University of Ibadan, PMB 5070, Ibadan, Nigeria. *[email protected]; osita.anyaeche@ ui.edu.ng http://doi.org/10.5281/zenodo.18061350 ARTICLE INFORMATION ABSTRACT Article history: Received 17 Aug. 2025 Revised 01 Nov. 2025 Accepted 09 Nov. 2025 Available online 30 Dec. 2025 The difference in the nature, volume, and types of waste, coupled with the inherent peculiarity of each environment, has necessitated the need for a sustainable integrated solid waste management (SISWM) framework that fits a particular locality with its inherent and current realities. This study aims to appraise the present state of Solid Waste Management (SWM) practices and present a feasible framework using both qualitative and quantitative techniques. Data collected from Ibadan, south-west Nigeria, using structured questionnaires and interviews were processed using Analytic Hierarchy Process (AHP) and system dynamics modelling and simulation. The result of the Analytic Hierarchy Process shows the major problems in their hierarchy, ranging from inadequate waste collection (0.647), inadequate budget (0.62), inconsistent waste legislation (0.531), inadequate awareness and education for the citizens (0.496), among others. The system dynamics model shows the feasibility of the proposed SISWM system, demonstrating its ability to hold down the waste generation below the waste collection capability of the system. Within the planning horizon. The model also serves as a metric for decision-making in solid waste management, future policy formulation, and practice. © 2025 RJEES. All rights reserved. Keywords: Sustainability Analytic Hierarchy Process System dynamics Integrated solid waste management Ibadan South-West Nigeria 1. INTRODUCTION The management of waste is basically the duty of the closest tier of government to the people in every city of the world (Mihai, 2017; Kaza et al., 2018). The urban cities of the developing world are witnessing an increasing trend of urbanization, leading to a rise in population, resulting in to rise in waste generation and waste management problems (Falola and Salm, 2004; Edomah, 2020; Kanojia and Visvanathan, 2021). Waste management activities and technology. There is little or no attention given to the issue of waste management practice in rural areas, especially in Africa, even with the geometric increase in population (Antwi et al., 2022; Bosompem et al., 2024; Nkululeko Zondi et al., 2023; 388 M.K. Oluwanimifise and C.O. Anyaeche / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 Schenck et al., 2022). This, coupled with a lack of other infrastructures and social amenities, is the reason for migration from the rural to urban slums, perpetuating their usual lifestyle of indiscriminate waste disposal and open defecation (Iyamu et.al., 2020; Shabani et.al., 2023). Some researchers (Hadidi et.al., 2020; Farooq et.al., 2021; He et.al., 2022) had earlier work on solid waste management systems and the increasing challenges it poses, proposing different frameworks. Cayumil et.al. (2021) examined the solid waste management in Chile and proposed a sustainable structure based on the inherent peculiarity of the environment. The waste management researchers have employed various tools to solve the continual problem of waste management. Some of these tools are: decision support system, internet of things (IoT), multicriteria decision making, system dynamics, to mention a few (Mohd Ijlal et.al., 2022; Saaty and Vargas, 2012; Gutierrez-Lopez, 2023). The lack of adequate planning of the ancient city of Ibadan and the slums in every nook and cranny was decried by UNDP. This was reported as a major impediment to adequate SWM in the pace-setter city. (UNDP, 2016, 2017). Shuster (1994) and Ogbe (2014) presented an engineering approach to the solid waste collection system. Fuss et.al. (2018) examined the obstacles and prospects in the solid waste management of the emerging economy countries of the world with the required synergy between the public and private agencies involved in solid waste management. Batista et.al. (2021), Abdel-Kader and Qutb (2023), Awino and Apitz (2023), opined that only an integrated solid waste management system (ISWM) is the possible solution to the waste management problem in populous and mixed societies of the developing world. Benefit (2014) emphasized the inevitability of social capital. That is, hearty and committed participation of all the stakeholders, as well as the need for a community-based Urban solid waste management (SWM). Numerous approaches, techniques, and tools have been used by the researcher to address the problems of waste management in the past. Some of these are scenario development and analysis (SD, SA), Expert systems (ES), Environmental impact Assessment (EIA), multicriteria decision making (MCDM), life cycle analysis (LCA), and decision support systems (Pires et al., 2011) Different tools like mixed integer programming, forecasting, dynamic programming, linear programming, and others have also been applied. Systems dynamics is a dynamic programming methodology that is used to analyse situations that change over time. Systems dynamics has proven to be effective in the modelling of complex systems with feedback. And loops (Forrester, 1961, 1969, 1971, 1980). Systems thinking and systems dynamics have been used extensively in the dumpsite selection problem as well as in other aspects of waste management (Forrester, 1992, 1994, 2015). Previous works have identified the areas of major challenges like: non-availability of adequate data for reliable appraisal, poor cost-recovery, no clear– cut strategy to measure the performance of SWM, inadequate capacity of some of the local waste contractors, no enforcement on the existing SWM legal structures, among others (Patil et.al.,2018; Rena et.al., 2022). These are used in this work to engage the waste management stakeholders in structured interviews. This study aims to determine the main problems in waste management in the study areas as well as their severity using a qualitative technique, Analytic Hierarchy Process, proffer feasible and sustainable solutions using a quantitative methodsystems dynamics. 2. MATERIALS AND METHODS 2.1. The Study Area The proposed SISWMS was calibrated using the data collected from Ibadan North Local Government Area in Ibadan, a populous sub-Saharan African city in south-western Nigeria. Ibadan North local government is chosen due to its centrality, coupled with the fact that it has the features that represent the entire Ibadan Metropolis. The Map of Ibadan North Local Government (LGA) inside Oyo state, showing the twelve wards, is presented in Figure 1. 389 M.K. Oluwanimifise and C.O. Anyaeche / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 Figure 1: The map of Ibadan North LGA (Source: UI Cartography Lab.) 2.2. Data Collection This study used respondents among the populace, waste management board, and public servants in the Ministry of Environment, Oyo Waste Management Agency (OYOWMA), private waste management companies, the researchers, and other stakeholders in the waste management business. A purposive sampling method was adopted to select the respondents based on their expertise, position, and experience in the waste management issues and management. Data collection was in the form of interviews to find out the waste management problems peculiar to the areas of study. The qualitative data from interviews were used to prepare the questionnaires and were later converted to quantitative data through the Analytic Hierarchy Process (AHP) method and then solved using spreadsheet modelling. Data were collected from the waste management handler, OYOWMA, as well as the people in the community about waste collection technique in operation, frequency of collection, and the kind of equipment in use, among others. 2.3. The Analytic Hierarchical Process (AHP) The hierarchical arrangement comprises two levels, namely: the goal, the main criteria, with their respective sub-criteria. The aspects considered are in line with previous works, which are based on a system approach to solving the waste management problems. Components comprise the human or social aspect, the policy and regulation aspect, the financial or economic aspect, and the technical or operational aspect. The social aspect addresses the extent of people's awareness, participation, training, and commitment to the waste management activities in their environment. The financial address the adequacy of the budget, separation of planning and execution documents, and determination of the priorities in the waste management (WM) activities. The policy and waste legislation aspect examines the sanctions and their implementation on waste management offenders, including the extent of deterrence in such sanctions. The operational aspect examines the adequacy of the waste equipment, waste haulers, and the activities. It examines the road access to some unplanned residential areas. The AHP structure for the SISWMS is presented in Figure 2. 2.4. The System Dynamics Model for the SISWMS The model is based on Forester’s synthesis approach, comprising the three models: waste generation, waste collection, and population model, dynamically linked together (Forrester, 1992, 2015). The overall waste target is the combination of the targets for each strategy. The waste collection method involves the use of a compactor, a hook loader, a refuse truck, direct labour, and a bulldozer, each having a distinct budget and effectiveness factor allocated to it. The important elements of the system are: waste generation, rate of waste generation, population, total waste stuck, waste collection, waste management cost, and waste management budget. Each equipment: refuse truck, compactor, hook loader, bulldozer, and direct labour is used to formulate strategies together with the target, budget, effectiveness, and funding attached to each of them. 390 M.K. Oluwanimifise and C.O. Anyaeche / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 Figure 2: The AHP structure for the SISWMS The specifications of the quantities and their respective unit are presented in Table 1: Table 1: The quantities of the system dynamics model and their units S/N Quantity description Dimension 1 Waste Management System (WMS), Budget Naira, N 2 Planned budget for each strategy Naira, N 3 Proportion of WMS budget actually used on each strategy Dimensionless 4 Planned or actual Budget Naira, N 5 Funding or Prop. of actual budget used Dimensionless 6 Waste collection (WC) Tons/Year 7 Waste generation (WG) Tons/Year 8 Waste generation rate Tons/person 9 Waste collection goal Tons 10 Generated waste Tons 11 The collection target of each strategy Tons 12 Effectiveness of each strategy Tons/naira 13 Frequency of waste collection 1/year 14 Waste generated factor 1/year 15 People concern Dimensionless 16 Population persons 17 Births persons 18 Birth factor Dimensionless 19 Deaths persons 20 Death factor Dimensionless 2.4.1. The causa loop diagram (CLD) for the SISWMS The elements of the model are presented using the causal loop diagram, which states and describes the major elements and their effects in the system. It shows the generation of waste and the collection process, as well as the influence of each element on one another in the WMS. The causal-loop diagram of the proposed SISWMS is presented in Figure 3: 391 M.K. Oluwanimifise and C.O. Anyaeche / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 Figure 3: The causal loop diagram for the SISWMS 2.4.2. The Stock and flow diagram (SFD) for the waste management system Consequent to the description of quantities in the system or having developed the Causal Loop Diagram (CLD), the stock and flow diagram (SFD) showing the interdependency and relationship of the quantities in the system is developed. The task attributes of the WMS are presented and quantified using the SFD presented in Figure 4. Figure 4: The Stock and flow diagram for the proposed SISWMS 3. RESULTS AND DISCUSSION This section presents the result of the overall values of AHP weighting, starting from the pairwise comparison of the main criteria and the sub-criteria. The values are within the acceptable level of critical ratio, which ranges from 0.01 to 0.09, to enhance consistency in the decision-making process. The values are presented in Figure 5: The sub-criteria are arranged in a hierarchy under every criterion. On top of the list in every aspect are: inadequate waste collection (0.647), inadequate budget (0.62), inconsistent waste legislation (0.531), and inadequate awareness and education for the citizen (0.496). The population and waste generation increase at a higher rate than the rate of increase in the budget for waste management. It reflects the reality on the ground, showing the need to increase the funding for WM activities, especially the waste collection aspect. The care-free attitude of the people with respect to waste management activities, as shown, requires a serious enlightenment campaign to correct the menace. The laxity in the legal and policy aspects of waste management practices worsens the case. Indiscriminate dumping of waste persists, as allowed by the stakeholders in that aspect. The existing waste legislation should be adequately enforced with commensurate deterrents to enhance adherence to the rules. freq.of gen waste generation generated waste waste collection freq of col. waste collection goal population Deaths Births + + ++ + + + -- + Budget for WMS Budget of each WM techniques Prop. of WM budget used on each techniques Target of WMS Effectiveness of WMS - + + + Budget Planned planned budget prop - + + - + DL Target DL budget DL effectiveness budget prop on DL WMS Budget planned WMS budget Actual WMS budget Over all Target Hook loader Budget Bulldozer budget Compactor budget Refuse Truck budget Hook loader target Prop of WMS on Hookloader Hook loader effectiveness Bulldozer budget prop Bull dozer target Bulldozer Effectiveness Target for compactor Compactor effectivenes Prop of WMS budget on Compactor Target for Refuse Truck Effectiveness of Refuse Truck Refuse Truck budget prop. waste stock waste generation collection of waste waste gen factor freq of waste collection population Births Deaths Birth factor death factor people concernwaste generation rate 392 M.K. Oluwanimifise and C.O. Anyaeche / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 Figure 5: The analytic hierarchy process results The waste collection aspect needs a total overhaul. The inefficiency and ineffectiveness are worrisome. Modern techniques peculiar to every locality should be explored to address the status quo. The system dynamic model was developed based on the operational characteristics and peculiarity of the system on the ground. The proportion of actual budget dispensed on the strategies using direct labour, refuse truck, compactor, bulldozer, and the hook loader was assumed to be 0.15, 0.10, 0.20, 0.25, 0.30, respectively. The effectiveness factor is the ratio of the target to the actual budget implemented for each strategy. The collection factor is 70% and the generation factor is taken to be 80 per year, with a planned budget of 380 million naira. The birth factor is taken to be 4.06% and the death factor is 2.5%. The model was run on Vensim PLE software (version 7). The summary of the outputs is presented in Figure 6. This shows the feasibility of the proposed system, demonstrating its ability to hold down the waste generation below the waste collection capability of the system despite the galloping increase in the population within the planning horizon (10 years). At the end of the planned period, an appraisal will be done to make necessary amendments in the operation characteristics of the system, thereby evolving a sustainable solid waste management system that is in line with the current realities in the environment. Some of the outputs from the Vensim software are presented in the appendix. A feasible framework based on a bottom-up approach is proposed in this work, called Sustainable Integrated Solid Waste Management (SISWMS). It gives the waste management task to the grass-roots government, which is the closest to the people, making use of the existing political structure in the local government council. The SISWMS makes use of waste treatment technology and policy that fit the environment socially, economically, and environmentally. The model takes care of all aspects of solid waste management and involves all stakeholders in constant assessment for a planning horizon of ten years per period, with a maximum of two periods before overhauling. The structure of the Model’s framework is presented in Figure 7. 393 M.K. Oluwanimifise and C.O. Anyaeche / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 Figure 6: The picture of the SISWMS performance in the planned Horizon Figure 7: The conceptual SISWMS model for Ibadan metropolis 4. CONCLUSION This work proposed a bottom-up approach to waste management based on the empirical findings obtained. The result of the Analytic Hierarchy Process shows the major problems in their hierarchy, ranging from inadequate waste collection (0.647), inadequate budget (0.62), inconsistency in the enforcement of waste legislation (0.531), inadequate awareness and education for the citizens (0.496), among others. The system dynamics model shows the viability of the proposed SISWMS as it keeps the population, waste generated, and waste collected in trends till the tail end of the planning horizon, when the system will be re-visited for adjustment. The model also serves as an instrument or metric for decision-making in the future. 0 500000 1000000 1500000 2000000 2500000 12345678910 11 Population (persons) Time (Years) Time(Year) Population(Persons) W(Tons) WG(Tons/Year) WC(Tons/Year) 394 M.K. Oluwanimifise and C.O. Anyaeche / Nigerian Research Journal of Engineering and Environmental Sciences 10(2) 2025 pp. 387-395 5. 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