Do Water Pollutant Reduction Projects Promote or Limit Carbon Reduction? Evidence from Building a Beautiful China

The total control of major water pollutants (TCMWP) is a critical strategy for improving water quality in China, with the added benefit of yielding climate-related advantages. This study uses the emission factor method to quantify the reductions in pollutants and carbon emissions resulting from China’s implementation of TCMWP. A synergy scale for pollution and carbon reduction was constructed to assess the co-benefits of reducing the Chemical Oxygen Demand (COD) and ammonium nitrogen (NH₄⁺-N) and carbon dioxide (CO₂) emissions. Furthermore, to account for regional variations in energy structure regulation strategies, whether aggressive or unified, we developed Pollutant Synergistic Carbon Reduction Pathways at the Regional (R.PSCRP) model framework level to evaluate the carbon emission reduction potential of TCMWP during the “14th Five-Year Plan” period. The study revealed that China’s unified TCMWP employs different but highly effective combinations of emission reduction paths across different regions. Notably, new renovations and expansions of wastewater treatment facilities (NRE-WWTFS) and pipeline network construction and renovation (CR-PNK) together accounted for 89.3% of the total emission reduction. The construction of key water pollutant reduction projects plays a significant role in reducing carbon emissions at the district level compared to direct discharge practices. Additionally, indirect emissions resulting from TCMWP implementation account for approximately 50% of the total carbon reduction achieved. By aligning either harmonized or independent energy adjustment targets, regions were able to achieve substantial pollution and carbon reduction benefits, ranging from 7.5 to 8 million tons of CO₂-equivalent.