Optimizing Municipal Solid Waste Management: P-Graph Studio Application For Resource Recovery In Nigeria’s Urban Centres

Abstract

Poor management of municipal solid waste (MSW) remains a critical challenge in Nigeria, particularly in rapidly urbanizing cities such as Lagos, where the pace of population growth outstrips the efficiency of existing waste management systems, thereby straining environmental, social, and economic resilience. Current models rarely incorporate stakeholder perspectives or provide context-specific decision-support tools, and the application of process network synthesis (PNS) in waste management planning across Sub-Saharan Africa remains limited. This paper applies P-graph-based PNS to identify optimal conversion pathways for four dominant waste streams: plastic, nylon, paper, and food waste, using five stakeholder-preferred conversion technologies: material recovery, incineration, pyrolysis, anaerobic digestion, and landfill. Ten optimized solution structures were generated through accelerated branch and bound (ABB) across four combinatorial spaces. Among the solutions, the third trial demonstrated the most balanced performance, with Structure 3 achieving 39,441.30 t/y greenhouse gas emissions, ₦133.35 billion/y profit, and substantial material recovery outputs (233,293 t/y nylon, 170,117 t/y paper, 305,061 t/y plastic, and 105,177 t/y solid and 157,765 t/y liquid fertilizers). In contrast, Structure 1 maximized profits (₦139.89 billion/y) but with higher emissions (45,820.70 t/y), Structure 8 excelled in energy recovery (363,698 MJ/y heat, 183,564 MWh/y electricity), and Structure 10 optimized bio-oil production (324,486 t/y). Notably, Structure 4 in the First trial achieved zero emissions but generated comparatively lower profits, while the second and fourth trials showed inconsistent outcomes. By minimizing landfill use and leveraging Lagos’s specific waste composition and stakeholder familiarity, the third trial’s Structure 3 best aligned with circular economy principles and the Sustainable Development Goals (SDGs) 7, 11, 12, and 13. The study concludes that investments in sorting infrastructure, anaerobic digestion, and pyrolysis, supported through public–private partnerships and active community engagement, are critical to ensuring scalability and sustainability. Overall, this PNS framework offers a replicable, stakeholder-informed decision-support model for Sub-Saharan African megacities, demonstrating how MSW can be transformed into resources for sustainable urban development while strengthening policy formulation, infrastructure planning, and resilient low-waste ecosystems.