Manuscript: DC Water’s Sewer-Methane Carbon Footprint

The Intergovernmental Panel on Climate Change (IPCC) has identified that sewers in the developing world do produce methane (CH4) but has in contrast proposed that wastewater in closed, and underground sewers in the developed world are not a significant CH4 source. Other greenhouse gas (GHG) emissions protocols have followed IPCC’s lead and have ignored sewer CH4. The protocols’ simplification has been routinely contradicted by research where significant CH4 emissions have been repeatedly detected from both pressure mains and gravity sewers.This paper reports the analysis of data collected as part of the Water Environment and Reuse Foundation’s (WE&RF) Conveyance Asset Prediction System (CAPS) Project (WERF Project Number U5R12). The project calibrated a sewer process model simulating sulfur- and carbon-based transformations and associated gaseous-phase emissions within the analyzed section of DC Water’s Potomac Interceptor (PI). A simplified algorithm that estimates sewer CH4 emissions on a basin- or collection-system-wide basis was then developed. The algorithm has been validated using the measured CH4 flux from the PI based on seasonal sampling. Finally, the simplified algorithm is extended to estimate the DC Water collection-system-wide CH4 emissions and the significance of these emissions within the context of the utility’s Scope-1 and Scope-2 emissions inventories over the same period of time.