Research On Calculation Of Water Environment Capacity And Pollution Prevention And Control Of Weihe River In Shaanxi Based On Process

The water quality of the main stream of the Shaanxi section of the Weihe River has been improved year by year,but there are still unstable changes in the water quality of some river sections and tributaries,sometimes good and sometimes bad.In order to further control the pollution of the water environment in the Shaanxi section of the Weihe River and maintain the health of the water ecology,it is of great practical significance to study the water environment capacity.Based on the National Natural Science Foundation of China and Shaanxi Provincial Key R&D Program Projects,with the Shaanxi section of the Weihe River as the research object,and COD_Cr and NH₃-N as the main pollution control factors.Data collection,field survey sampling,indoor experiment and numerical simulation are used to analyze the temporal and spatial changes and driving forces of the water quality of the Shaanxi section of the Weihe River.Based on the water quality model and the mathematical model of water environment capacity,the water environment capacity and pollutant reduction are calculated.It also discussed the influencing factors of the water environment capacity of the Shaanxi section of the Weihe River in order to propose water pollution prevention and control countermeasures.The main achievements are as follows:（1）The water quality status,water volume changes,population,economy,and pollutant discharge of the Shaanxi section of the Weihe River are analyzed.From 2015 to 2019,the content of COD_Cr and NH₃-N in the monitored sections of the Shaanxi section of the Weihe River decreased year by year,and the water quality became better year by year.The measurement results of the main stream and tributaries of the Shaanxi section of the Weihe River Basin found that the water quality of the main sections of the Weihe River,such as Tianjiang Rendu and Xinfeng,was the worst,and the tributaries had the worst water quality in the Alkali Drainage Canal in Weinan City.Due to the discharge of industrial pollutants,agricultural pollutants,domestic pollutants and animal husbandry pollutants,the emission of COD_Cr and NH₃-N in the Shaanxi section of the Weihe River reached 369,600 t/a and 54,500t/a,and the pollution load remained high.（2）Based on comprehensive analysis of the hydrological characteristics of the Shaanxi section of the Weihe River,a water quality model and a water environment capacity model for the Shaanxi section of the Weihe River were established.Based on the measured values,the accuracy and reliability of the one-dimensional and two-dimensional simulation results are verified.According to the set water quality targets of the Shaanxi section of the Weihe River,the water environment capacity of the Weihe River is calculated by the control method of breaking the head and the end of the Weihe River.Under the flow guarantee rates of P50,P75and P90,the COD_Cr water environmental capacity of the Shaanxi section of the Weihe River is508,500 t/a,262,600 t/a and 167,800 t/a,respectively,and the NH₃-N water environmental capacity is 30,700 t/a./a,16,500 t/a and 10,700 t/a;the reduction of COD_Cr in the Shaanxi section of the Weihe River is:-139,000 t/a,107,000 t/a and 201,800 t/a;reduction of NH₃-N They are 23,700 t/a,37,900 t/a,and 43,200 t/a.The results show that the water environmental capacity of COD_Cr and NH₃-N is Weinan section>Xi’an section>Xianyang section>Baoji section,and the section with the largest reduction of COD_Crand NH₃-N is Xianyang-Tianjiang rendu,followed by Nanying-Xianyang River segment.（3）Based on the calculated water environmental capacity and pollutant reduction in different sections of the Weihe River in Shaanxi,the influence of environmental factors such as Weihe River discharge,water quality concentration and degradation coefficient on the water environmental capacity was revealed.Through the above research,it is concluded that the water environment capacity is positively correlated with flow rate and degradation coefficient,and negatively correlated with water quality concentration.Aiming at the current situation of water quality changes,pollution load,water environmental capacity and pollutant reduction in the Shaanxi section of the Weihe River,comprehensive pollution prevention and control measures such as increasing the ecological flow in the middle reaches,reducing the concentration of pollutants in the middle and lower reaches and increasing the comprehensive degradation coefficient of downstream water quality are proposed.