Transport Characteristics And Water Environmental Capacity Of Characteristic Pollutants In Lanzhou Section Of The Yellow River

Conducting evaluation of water environment carrying capacity,balancing sea and land basin and promoting emission reduction and capacity increase by focusing on improvement of the aquatic environment quality is significant for local water pollution control,ecological protection and quality improvement of water ecological environment.According to the work plan for water pollution prevention and control in 2019 in Gansu Province?No.10[2019]issued by Gansu Provincial Water Pollution Prevention and control leading office?,status assessment of water resource and water environment carrying capacity for Lanzhou should be accomplished before the end of 2019.Therefore,it is very important to analyze water quality of basin by means of water quality model and determine emission reductions according to water environmental capacity.This paper chose Lanzhou section of the Yellow River as the research object to evaluate the water quality of Xincheng bridge section and Baolan bridge section on the basis of natural features,hydrological conditions,water environmental overview and water quality monitoring results in 2013-2019 of river.Simulation was carried out of transportation characteristics of characteristic pollutants and water environment capacity by using one-dimensional steady-state and two-dimensional water quality models,and water quality in 2020 and 2023for this river was predicted.?1?Combined with single factor evaluation method,the water quality of Xincheng bridge section and Baolan bridge section from 2013 to 2019 was evaluated according to the status of water environment of Lanzhou section of the Yellow River.The evaluation results show that:The indexes of the sections of Xincheng bridge and Baolan bridge from 2013 to 2019 meet the requirements of class II and class III water quality standards specified in environmental quality standard for surface water?GB3838-2002?.From the perspective of the two sections,COD_Cr,ammonia nitrogen,BOD₅,TP and petroleum have relatively small average standard ratio;in addition,since 2016,all pollutants have different degrees of decline and fluctuation,which reflects the governance effect of Lanzhou Ecological Environment Bureau,making room for the water environment capacity of Lanzhou section of the Yellow River.?2?Based on one-dimensional steady-state water quality model,the concentration of featured pollutants was calculated using MATLAB program by four-point implicit difference method.The calculating methods of the water quality parameter such as velocity,comprehensive degradation coefficient,transverse diffusion coefficient and dispersion coefficient were determined,and the parameters were calibrated with the contrasted analysis between modeling values and measured values of water quality of Xincheng bridge section,and the results show that the simulation error of this one-dimensional water quality model meets the requirements.?3?The simulation of water quality current situation of Lanzhou section of the Yellow River in January,2017 was made by using numerical solutions of one-dimension model and analytic solutions of two-dimension model.The simulation results include two positive correlations,that is,the increment of the downstream section of the sewage outlet is positively correlated with the discharge volume;the length of the pollution zone is positively correlated with the discharge intensity;and the results show that the analytic solutions two-dimensional water quality model was in accordance with the physical circumstances.?4?The water environment capacity of characteristic pollutants(COD_cr,ammonia nitrogen,Petroleum,BOD₅,TP)at Lanzhou section of the Yellow River were calculated by using one and two dimensional water quality models,and the two-dimensional water quality model was selected to calculate residual water environmental capacity,the calculation results are as follows:1395 t/a?1609.8 t/a?68.4 t/a?4030.2 t/a and 75.5 t/a.Combined with two-dimensional water quality model,the water quality of COD_cr and ammonia nitrogen at Baolan bridge section was predicted through analysis and forecast to sewage of waste water and pollutant discharge producing from industry and domestic wastewater.It showed that the predicted water quality of Baolan bridge section did not exceed the standard by contrasting predicted results with water quality standards of functional divisions of the reach.