Anaerobic digestion or composting? Small-scale plants design and holistic evaluations in a Sub-Saharan African context

Abstract

In small developing settings, is it worth building anaerobic digestion (AD) or composting plants? This study explores the economic, management, and environmental dimensions of two small-scale alternatives for organic fraction municipal solid waste (OFMSW) treatment within the context of Lacor Hospital (Uganda): aerated static pile composting (S1) and AD with digestate composting (S2), both designed to manage approximately 347.5 t_OFMSW annually. In the optimistic scenario, S1 achieves a cost savings of about −2.9 USD t_OFMSW⁻¹, while S2 incurs costs of 2.1 USD t_OFMSW⁻¹. In the pessimistic scenario, S1's costs rise to 3.9 USD t_OFMSW⁻¹, while S2 becomes more expensive at 9.5 USD t_OFMSW⁻¹. Management analysis underlines S2's complexity due to AD operations and digestate drying. Total normalized environmental impacts of S1 can be quantified with about 0.125 mPt t_OFMSW⁻¹, whereas S2 is equal to about −6.163 mPt t_OFMSW⁻¹. However, in an optimistic scenario, climate change endpoint category results are similar. On balance, the LCA analysis indicates that AD can be better than standalone composting. However, in developing settings serving approximately 3000 inhabitants, it is crucial to prioritize economic and management sustainability that can be obtained only by small-scale composting plants. These findings provide definite insights for small-scale waste management projects in low-income regions, offering valuable data and references for plant design and their replicability. The study sets the ultimate definition of the most feasible option to treat OFMSW in low-income settings: community composting. Unfortunately, economic barriers remain the main challenge: citizens should pay for the service and landfill management fees should be set by local governments.