Revisiting China's domestic greenhouse gas emission from wastewater treatment: A quantitative process life-cycle assessment.

The wastewater treatment industry could alleviate water pollution but consume a large amount of energy and resources. China has over 5000 centralized domestic wastewater treatment plants and produces an unignorable amount of greenhouse gases (GHG). By considering the wastewater treatment, wastewater discharge, and sludge disposal processes, and employing the modified process-based quantification method, this study quantifies wastewater treatment's on-site and off-site GHG emissions across China. Results showed that the total GHG emission was 67.07 Mt CO2-eq in 2017, with approximately 57% of on-site emissions. The top seven cosmopolis and metropolis (top 1%) emitted nearly 20% of the total GHG emission, while their emission intensity was relatively low due to the huge population. This means that a high urbanization rate may be a feasible way to mitigate GHG emissions in the wastewater treatment industry in the future. Furthermore, GHG reduction strategies can also focus on process optimization and improvement at WWTPs as well as the nationwide promotion of onsite thermal conversion technologies for sludge management.