Estimation of greenhouse gases from sewage from on-site sewage management system

Abstract

Reducing greenhouse gases (GHGs) emissions plays an important role in preventing global warming and climate change. It is generally known that domestic wastewater management activities are significant contributors to the emissions due to its biological process that produces methane, nitrous oxide, and carbon dioxide. Various studies related to GHGs emissions from this sector have been conducted. However, only limited studies focused on the on-site sewage treatment. Since 72% of total existing wastewater treatment facilities in Indonesia are on-site systems, this study attempted to estimate GHGs emissions from each component in the system using the IPCC method. Depok City was chosen as the study case and the estimation was limited to on-site treatment tank, wastewater collection tank, and fecal sludge treatment system. Our study estimated that the total annual emissions from the on-site sewage system in Depok City were 232.45 Gg CO2eq, consisted of 232.39 Gg CO2eq of on-site emissions and 0.0662 Gg CO2eq of off-site emissions. Among the system component, direct emissions from the on-site treatment such as septic tanks is the highest contributor to the total emission (70% followed by direct emission from fecal sludge treatment plant (19%). Through scenario evaluations, this study suggests that converting private septic tanks into the communal type is the most effective strategy in reducing total GHGs emissions from on-site wastewater treatment systems.