Statistical Analysis of Global Warming Potential, Eutrophication Potential, and Sludge Production of Wastewater Treatment Plants in Japan

Abstract

Treatment performance and greenhouse gas emissions of various biological sewage treatment processes in Japan were evaluated. Data related to energy consumption, effluent water quality, and sludge production of various treatment processes were obtained from “Sewage Statistics” published by the Japan Sewage Works Association. The conventional activated sludge (CAS) process and modified processes for nutrient removal were selected for analysis, such as anaerobic–oxic, recycled nitrification–denitrification, anaerobic-anoxic–oxic, nitrification/endogenous denitrification, and step-feed nitrification–denitrification processes. Performance of the treatment processes was evaluated as the eutrophication potential (EP) calculated from the BOD, total nitrogen, and total phosphorus concentrations in treated effluent and NOX emission by electricity consumption. The global warming potential (GWP) of treatment processes was calculated from CO₂, CH₄, and N₂O emissions by electricity consumption, and N₂O and CH₄ emissions from the biological processes and water environment where effluent is discharged. The EP values of the nutrient removal processes (1.0–6.4 g-PO₄eq/m³) showed negative correlation with the GWP values (0.22–0.68 kg-CO₂eq/m³) as a general trend. The sole exception to this tradeoff was the step-feed nitrification–denitrification process, which can reduce the EP value of sewage with a considerably smaller increase of the GWP value than that of the CAS process. Sludge yields of treatment processes (0.01–0.032 m³/m³) also showed negative correlation with GWP values.