Research on the environmental capacity and total control of main pollutants in the Jiaxing waters

In recent years, the marine ecological environment quality in the Jiaxing waters has significantly deteriorated. Implementing total pollutant control measures as one of the fundamental measures to ensure the quality of the marine environment is conducive to reducing emissions and controlling pollutants in the Jiaxing waters, thereby safeguarding the sustainable development capacity of the area. Based on the hydrodynamic-water quality model of the adjacent waters of Jiaxing and field monitoring results, and in accordance with the water quality requirements of the environmental functional zoning of coastal waters in Zhejiang Province, the response coefficient method and linear programming method were adopted to calculate the environmental capacity of chemical oxygen demand (COD), inorganic nitrogen, and phosphate for the important discharge outlets in the area. Calculations and evaluations were carried out for the total control measures affecting reduction and expansion. The results indicate that the total environmental capacity of COD in the research area is 2.97×10⁵ tons/year, with a considerable surplus. However, the content of inorganic nitrogen and phosphate exceeds the fourth-class seawater quality standards, surpassing the environmental capacity of inorganic nitrogen and phosphate in the area. Rational quantified numerical simulations of existing plans show that although reduction measures have stabilized the increase in COD, inorganic nitrogen, and phosphate caused by expansion to some extent, it is still necessary to continue optimizing sewage treatment capacity and reducing the discharge of nitrogen and phosphorus nutrients. The research results can provide a scientific basis for the study of total pollutant control in coastal cities.