Can Data Mining Improve Methane Correction Factors for Urban, Nonsewered Sanitation?

Nearly half of the world's population relies on nonsewered sanitation, and in urban areas, intermittent onsite storage of wastewater prior to road-based transport to treatment is common. Anerobic biological activity during storage generates methane, contributing to greenhouse gas emissions and posing challenges for climate mitigation. Current estimates of methane emissions rely on methane correction factors (MCFs) in the Intergovernmental Panel on Climate Change (IPCC) guidelines that are based on theoretical assumptions and increasingly viewed as not valid. In this Perspective, we use 1349 data points from onsite storage of wastewater in 11 cities to show that obtaining accurate city-wide estimates is complicated by highly variable properties of in situ wastewater and storage conditions and hence biological production of methane. When it comes to greenhouse gas emissions from nonsewered sanitation, the sector has so far focused on storage, but as evidence suggests these estimates are too high, we propose that emphasis should in fact be placed on the entire service chain.