Research on optimal allocation and evaluation of allowable pollutant discharge in Zhangjiakou section of Yongding River

The environmental Gini coefficient was used to analyze the influence of land, population and gross domestic product (GDP) on chemical oxygen demand (COD_Cr) discharge of water pollutants in Zhangjiakou section of Yongding River Basin. At the same time, the distribution coefficient of each control unit was optimized by maximizing the utilization of environmental efficiency and minimizing Gini coefficient model, and a relatively fair distribution reduction scheme was made by environmental Gini coefficient method. The contribution coefficient of each control unit was calculated, the unfairness factor was judged, the spatial difference of the unfairness factor in the study area was analyzed, and the reasonable suggestions on regional development model were put forward. The results showed that the environmental Gini coefficient of each control unit based on land area, population and GDP was 0.504 4, 0.306 8 and 0.234 1, respectively, and the Gini coefficient based on land area was far beyond the warning value. Among COD_Cr discharge reduction schemes obtained after optimized allocation, Xuanhua District of Zhangjiakou City should have the highest reduction rate of 16%. According to the analysis of contribution coefficient, the contribution coefficient of Zhangjiakou downtown area was less than 0.5, and the unfairness was the most prominent. It was suggested that the regional industrial structure should be adjusted appropriately to improve the utilization rate of resources and reduce the discharge of pollutants.