Sector-wide GHG Emissions with Normalized Process and Effluent N2O, Sewer CH4, and Methanol CO2

Sewer methane (CH4) and methanol carbon dioxide (CO2) have been poorly covered in greenhouse-gas (GHG) emissions protocols. Domestic-sewage treatment nitrous oxide (N2O) has been treated either holistically on a population-based basis or more recently split out to differentiate N2O emitted from biological processing of nitrogen and by effluent-nitrogen discharge and subsequent production of N2O from biological processes in the receiving environment. Willis et. al (2017) and Willis et. al (2020) used DC Water GHG inventories before and after digestion upgrades at the Blue Plains Advanced Wastewater Treatment Plant (Blue Plains) to estimate that methanol (CH3OH) CO2 and sewer- CH4 respectively represented 55.5% and 12.8% of the US centralized-sewage treatment industry’s Scope GHG emissions. These publications noted that, due to the use of Blue Plains’ extremely low process N2O emission rates, that process N2O was necessarily under-accounted for in those national estimates. This paper coordinates those prior estimates with process-specific N2O emissions to provide an initial, better-reconciled assessment of the US wastewater industry’s Scope-1 GHG emissions.