Mitigation of wastewater CH4 emissions was largely unaddressed in the studies compared to landfills or natural gas. This could be due to the comparatively low emissions relative to city-level totals (e.g., or the poor scalability of current solutions to reduce CH4 emissions from urban wastewater networks . Anaerobic digesters at WWTPs were identified as notable emissions sources in aerial and vehicle-based system surveys across California and other areas of the U.S. . These emissions reduce the mitigation effectiveness of the digesters but to what extent is unclear.