Greenhouse gas emission characteristics and mitigation pathways of wastewater treatment plants based on monthly emission data

This study investigates the dynamic greenhouse gas (GHG) emissions of four urban wastewater treatment plants (WWTPs) employing distinct processes (Plant A: OD-CASS; Plants B/C: A2O; Plant D: A2O-MBR) using 2022 monthly operational data. Referring to the emission factors provided in the Technical Guidelines for Carbon Accounting and Emission Reduction Pathways in Urban Water Systems, which better reflect China’s regional characteristics, this study analyzes the spatiotemporal patterns and driving mechanisms of direct emissions(CH₄, N₂O, sludge carbonization), indirect (electricity, chemicals, transportation), and GHG reduction (Photovoltaic Power Generation(PV), reclaimed water reuse) pathways. Key findings reveal: (1) Substantial process-specific emission intensity variations (0.26 - 0.88 kg/m³), with Plant D exhibiting the highest intensity due to membrane energy demands, while Plants B/C achieved lower intensity through flexible return ratio adjustments; (2) Indirect emissions dominated total emissions, primarily driven by electricity consumption; direct N₂O emissions were also significant; (3) Inflow organic load (Qr, R ̅=-0.76) and total nitrogen (TTN, R ̅=0.89) emerged as critical intensity influencers, while biochemical oxygen demand (TBOD₅, R ̅=0.68) and chemical oxygen demand (TCOD, R ̅=0.67 also showed significant positive correlations; (4) Existing GHG reductions (PV: 3.5% neutrality; reclaimed water: 7.3 - 14.5%) remain insufficient for neutrality goals. The study underscores the necessity for integrated strategies combining operational optimization, process selections, resource recovery technologies, and policy incentives to achieve dynamic GHG management in municipal WWTPs.