Biomethane production from market organic waste components : a multi-criteria selection, co-digestion and techno-economic assessment

Abstract

In Kampala, urban markets generate substantial quantities of market organic waste (MOW), whose management imposes significant economic burdens due to high collection, transportation, and disposal costs, while also contributing to greenhouse gas emissions. Anaerobic digestion (AD) offers a sustainable pathway for converting MOW into biomethane (BioCH4), thereby simultaneously addressing waste management challenges and enhancing access to renewable energy. However, existing literature provides limited guidance on how to systematically ascertain the feasibility of BioCH4 production from heterogeneous MOW components. This study therefore developed an integrated framework to evaluate BioCH4 production from MOW, using Kalerwe market as a case study due to its high waste generation and central role in Kampala’s fresh produce supply chain. The framework combined MOW component selection, experimental AD optimization, and techno-economic analysis (TEA). Key MOW components were selected using a multi-criteria decision-making approach that integrated the Analytical Hierarchy Process (AHP), Entropy Weight Method (EWM), and Weighted Linear Combination (WLC) based on waste composition and theoretical methane potential (BMPth). Co-digestion experiments were then conducted using an augmented simplex-centroid design to optimize substrate mixtures and maximize BioCH4 yield. The Scale-up feasibility was then assessed through TEA using SuperPro Designer, evaluating three distinct scenarios (1, 2 and 3) based on the optimal mixture and actual daily waste quantities from the market. Banana waste (BW), yam waste (YW), and jackfruit waste (JFW) were identified as the most promising components. The optimal mixture (3.00% YW, 74.18% BW, 22.82% JFW) achieved a maximum cumulative methane potential (CMP) of 86.23 mLCH4/gVS. However, observed CMP values fell below theoretical estimates, primarily due to volatile fatty acid (VFA) accumulation, pH decline, and consequent inhibition of methanogenic activity with effects particularly pronounced in YW-rich mixtures. TEA results confirmed the viability of all scenarios, with Scenario 2 (BW baseline) exhibiting the highest performance: 44.49% return on investment (ROI), 74.96% gross margin, 2.25-year payback period (PBP), 52.11% internal rate of return (IRR), and $15.296 million net present value (NPV). Overall, the study demonstrates a structured and transferable framework for MOW valorisation that integrates feedstock selection, process optimization, and economic evaluation to support sustainable waste-to-energy systems in urban market settings.