Costs and benefits of biogas recovery from communal anaerobic digesters treating domestic wastewater: Evidence from peri-urban Zambia

Abstract

Communal anaerobic digesters (ADs) have been promoted as a waste-to-energy strategy that can provide sanitation and clean energy co-benefits. However, little empirical evidence is available regarding the performance of such systems in field conditions. This study assesses the wastewater treatment efficiency, energy production, greenhouse gas (GHG) emissions, and financial costs and benefits of communal ADs used for domestic wastewater treatment in Zambia. Primary data on the technical performance of 15 ADs were collected over a 6-month period and in-person interviews were conducted with heads of 120 households. Findings from this study suggest that ADs offer comparable wastewater treatment efficiencies and greater GHG emission reduction benefits relative to conventional septic tanks (STs), with the greatest benefits in settings with reliable access to water, use of low efficiency solid fuels and with sufficient demand for biogas in proximity to supply. However, absent a mechanism to monetize additional benefits from biogas recovery, ADs in this context will not be a financially attractive investment relative to STs. Our financial analysis suggests that, under the conditions in this study, a carbon price of US$9 to $28 per tCO2e is necessary for positive investment in ADs relative to STs. Findings from this study contribute empirical evidence on ADs as a sanitation and clean energy strategy, identify conditions under which the greatest benefits are likely to accrue and inform international climate efforts on the carbon price required to attract investment in emissions reduction projects such as ADs.