Flexible Carbon Source Regulation for Mitigating Greenhouse Gas Emissions in Full-Scale Wastewater Treatment

Achieving carbon neutrality in wastewater treatment plants (WWTPs) by 2060 requires effective strategies to mitigate greenhouse gas (GHG) emissions. This study explores the potential of flexible carbon source regulation to reduce GHG emissions while improving the nutrient removal efficiency under varying influent conditions. A plant-wide model was developed, calibrated with one year of hourly monitoring data, to quantify GHG emissions in a full-scale WWTP. We evaluated three carbon regulation strategies: anaerobic digestion (AD), short fermentation (SF), and adaptive carbon source regulation (ACSR). Results show that AD was most effective in high carbon-to-nitrogen (C/N) ratios, reducing GHG emissions by 29.2%. SF performed best at low C/N ratios, reducing N₂O emissions by 56.3%. The ACSR strategy, which dynamically adjusts between AD and SF based on influent C/N, achieved a total GHG reduction of 18.2% compared with the base strategy (conventional activated sludge process with mechanical dewatering and landfill disposal of waste sludge). Seasonal variations significantly impacted emissions (p < 0.001), while C/N ratios, although not statistically significant in isolation, play a crucial role in influencing N₂O emissions and sludge production, emphasizing the need for adaptive carbon allocation. This study underscores the viability of plant-wide, data-driven carbon source regulation as an integrated approach to achieving net-zero emissions in WWTPs, effectively addressing diverse GHG emission sources within the system.