Benchmarking Greenhouse Gas Emissions from U.S. Wastewater Treatment for Targeted Reduction

To assess the national climate impact of wastewater treatment and inform decarbonization, we assembled a comprehensive greenhouse gas inventory of 15,867 facilities in the contiguous United States. Considering facility location and treatment configurations, we model on-site CH4, N2O, and CO2 production, and emissions associated with energy, chemical inputs, and solids disposal. Our estimate of 42 million tonnes CO2-eq·year-1 is over 25% higher than current government national wastewater inventories. Without leak detection and repair programs, facilities with anaerobic digesters currently are responsible for 17 million tonnes CO2-eq·year-1 of fugitive methane, outweighing the greenhouse gas offsets achieved through on-site electricity generation. Treatment configurations designed for nitrification have the highest greenhouse gas emissions intensity, attributable to high energy requirements and N2O production, and demonstrating current trade-offs between meeting nutrient removal and climate objectives. We include a geospatial analysis to highlight the scale and distribution of opportunities to reduce life cycle greenhouse gas emissions.