Impact of GHG mitigation measures in sanitation service chains: focusing on septic tanks and sewers

Sanitation service chains (SSC) in many cities in low- and middle-income countries are complex and comprise poorly managed on-site and centralized technologies that emit greenhouse gases (GHG). In this study, we aimed to estimate the impact of GHG mitigation measures along SSCs and account for the interdependencies of SSC components with respect to GHG emissions. Using an SSC in Hanoi, we employed a mass balance approach, empirical emission equations, and a carbon footprint estimation model to estimate GHG emissions by component at baseline and four mitigation scenarios. At baseline, the SSC emitted 3,698–5,147 ton CO2e/year, with CH4 accounting for 78–85% of the total emissions. Infrequently emptied septic tanks accounted for 44–60% of the total emissions, followed by poorly maintained sewers (23–32%) and a wastewater treatment plant (WWTP, 17–24%). Scenario comparison showed that removing septic tanks alongside sewer improvement led to 15–24% lower GHG emissions compared to frequent septic tank emptying with sewer improvements, despite a slight increase in the N2O emissions at the WWTP. Therefore, if not removed, septic tanks will remain an important source of GHG emissions even after a centralized sanitation is established. However, their removal may pose significant social challenges.