Synergistic benefit assessment of reductions in pollution and in CO₂ emission and green low-carbon operation strategies for urban recycled water plant with A²O process

To explore the synergistic benefits of reductions both in pollution and in carbon emission, and carbon emission reduction potential of urban recycled water plants, a recycled water plant with A²O process at a capacity of 600 000 m³·d⁻¹ was studied. A synergistic evaluation system for reductions in pollution and in carbon emission was established. A baseline scenario (BAU, business as usual), technology optimization scenarios (hypothesis 1, hypothesis 2), was set up. Five sub-scenarios (S1-S5) of reduction in carbon emission, and a comprehensive scenario (S6) were all studied. Quantitative analysis was done combining monitoring data and simulation models. For reduction in pollution, the removal rates of COD, BOD₅, SS, NH₃-N, and TP all reached over 95% (with TN removal rate ranging from 64% to 78%), with the effluent meeting Discharge Standard of Water Pollutants for Municipal Wastewater Treatment Plants (DB11/ 890-2012). The pollution reduction index score reached an excellent level. For reduction in carbon emissions, average carbon emission reduction score under the baseline scenario was 77.2 (Grade C). The scenario implementing technologies such as sludge resource utilization, solar photovoltaic, and water-source heat pump increased the average carbon emission reduction score to 92.0 (with a growth rate of 19.2%). Comprehensive emission reduction scenario S6 raised the carbon emission reduction index score from baseline 77.2 to 92.0, with an increase of 19.2%. For synergistic benefits, comprehensive score of pollution reduction and carbon emission reduction under the baseline scenario was 87.7 (Grade B), and after technology integration, the comprehensive score reached 95.1 (excellent level). In scenario S6, the comprehensive score of green low-carbon operation of the recycled water plant was 8.4% higher than that under BAU, the inter-annual carbon emission intensity decreased to 0.297 kg·m⁻³, and the carbon emission intensity per unit of wastewater decreased by 0.8%. This study indicates that resource recoveries and clean energy utilization technologies are core to improving the synergistic benefits of pollution reduction and carbon emission reduction in recycled water plants. This provides efficient technical support for recycled water plants to integrate into “dual-carbon” management.