Quantifying Methane Evolution From Sewers: Results from WERF/Dekalb Phase 2 Continuous Monitoring at Honey Creek Pumping Station and Force Main

Collection systemwide methane (CH4) emission estimates are being developed from field sampling in DeKalb County, Georgia as part of Water Environment Research Foundation (WERF) project U2R08 – entitled “Methane Evolution from Wastewater Treatment and Conveyance.” This task has been implemented in several phases of field monitoring and data collection. This paper presents initial findings of the Phase 2 of this task.The goal of the first phase of the investigation was to determine if CH4 could be detected in the wet wells and forebays of a sanitary wastewater collection system. Instantaneous CH4 measurements at 65 pumping stations across the entire county were quantified during Phase 1. The results of that investigation documented that approximately 1,000 MT of carbon dioxide equivalents (CO2e) are emitted each year from CH4 evolution at pumping stations. While 1,000 MT CO2e/yr were quantified, significant sources of under reporting are thought to exist. Specifically, during Phase 1, gravity sewers and manholes where force mains discharge were not monitored.During Phase 2, continuous monitoring for CH4 was conducted at the discharge of a 16–inch, 3.3– mile–long force main from the Honey Creek Pumping Station (HCPS) and at the enclosed wet well of the Stone Mountain Park Lift Station (SMPLS) that exhibited high Phase 1 CH4 measurements. Systems were monitored under normal operation for CH4 and hydrogen sulfide (H2S) emissions. To study the effects of electron acceptor addition on the force main CH4 evolution, Sodium Nitrate (NaNO3) was also dosed at HCPS during Phase 2.Overall, the results form the continuous monitoring during Phase 2 suggest that the collection systemwide emissions are likely considerably higher than the 1,000 MT of CO2e/year identified during Phase 1. It also suggests that force main discharge locations warrant additional investigation.