Evaluation of the Synergistic Performance of Wastewater Treatment Plants for Pollution and Carbon Reduction.

With the continuous advancement of urbanization， the construction of wastewater treatment plants （WWTPs） in China is developing rapidly， but there is a lack of synergistic research on pollution and carbon reduction in WWTPs. To quantify the synergistic effect of pollution and carbon reduction， a synergistic performance evaluation system for pollution and carbon reduction at WWTPs was constructed. The coupled coordination model was used to calculate the synergy index of pollutant reduction， carbon emission reduction， and cost control system， and the synergistic effect of pollution and carbon reduction of 640 WWTPs in southern China was evaluated. Finally， the influencing factors of the synergy index of pollutant and carbon reduction were further investigated by Spearman's correlation coefficient. The results firstly showed that WWTPs with the A2/O process performed best in terms of pollutant reduction， with higher pollutant reduction per unit of effluent； WWTPs with the A2/O process and SBR-type process had lower carbon emission intensity per unit of effluent， demonstrating a good carbon emission reduction； and WWTPs with a scale of more than 50 000 t·d-1 had the lowest cost per unit of effluent treatment， showing strong cost control ability. Secondly， nearly 80% of WWTPs had realized a better pollution reduction and carbon synergy effect， reaching a highly coordinated level， especially the WWTPs with the A2/O process. The pollution and carbon reduction synergy effect improved as the scale of the WWTPs became larger. Thirdly， the synergy index was positively correlated with pollutant indicators， but it was negatively correlated with carbon emission intensity and cost indicators. The comprehensive reduction of pollutants per unit of wastewater was the most strongly positively correlated indicator， while the cost of treatment per unit of wastewater was the most strongly negatively correlated indicator. The study showed that WWTPs should urgently develop energy-saving green transformation paths and measures in carbon emission and cost control on the basis of pollutant emission standards.