Plant-wide study of greenhouse gas emissions and biological CO2 mitigation in municipal wastewater treatment plant

초록

Municipal wastewater treatment plants (MWTPs) are both sources of greenhouse gases (GHGs) and platforms for biological mitigation through integrated process control. This study quantifies plant-wide GHG emissions and biological CO2 mitigation potential in a full-scale MWTP treating combined domestic and industrial wastewater under low-DO (dissolved oxygen) biological nutrient removal and anaerobic digestion. Long-term operational data, targeted laboratory experiments, and stoichiometric carbon–nitrogen balances were integrated to determine CH4, CO2, and N2O emission factors for major liquid- and sludge-line units and to clarify transformation pathways. Aerobic biological oxidation was the dominant direct CO2 source, with emission factors of 0.49–0.61 kg CO2/kg COD, which agreed with stoichiometric predictions, while anaerobic digestion and sludge storage were the main CH4 contributors but also key mitigation levers when gas capture and utilization were effective. Carbon redirection from the aerated liquid line to the sludge line reduced aerobic CO2 release and enhanced methane-rich biogas recovery (67% CH4), thereby enabling a net CO2-equivalent reduction without major infrastructure changes. N2O showed high emission potential under low-DO and transient laboratory conditions but remained negligible at full scale under stable low-DO operation, underscoring the importance of robust nitrification control. Overall, the results highlight plant-wide biological optimization, combining low-DO operation, carbon partitioning, and improved sludge-line management, as a practical strategy for MWTPs with high industrial wastewater fractions and energy-positive anaerobic digestion to achieve lower carbon emissions. © 2026 Elsevier Ltd.

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