Research On Evaluation And Prediction Of River Water Quality For Sewage Treatment Plant Tail Water Replenishment

The Xinmi section of the Shuangji River Basin is located between shallow hills and mountains,surrounded by mountains on three sides,and basically no external runoff water supply.It belongs to an urban tailwater river in the shallow hills and mountains.The main water source of the river is urban tail water,which mainly includes the drainage of urban domestic sewage plants and industrial sewage plants.The research on this urban tailwater river is of practical significance for controlling and reducing pollutants in the drainage basin.It has certain reference and reference value for the future research on the water environment problems of other urban tailwater rivers in my country and the impact of urban tailwater replenishing surface water.The water environment management of Shuangji River Basin provides data and technical support.Based on field investigations,this study selected 8 main stream monitoring points and 6 tributary monitoring points in the Xinmi section of the Shuangji River Basin for a two-year water quality monitoring.Each monitoring point monitored 19water environment factors per month,a total of 6,384 monitoring data were obtained.Apply single factor evaluation method,Nemerow index method,cluster analysis,principal component analysis and factor analysis to analyze the temporal and spatial distribution characteristics of the monitoring data and analyze the pollution source.According to the results of pollution source analysis,five key factors were selected for residual correction GM（1,1）model water quality prediction,based on the results of water quality evaluation and prediction,combined with field investigations within two years,the main pollution causes of the Xinmi section of the Shuangji River Basin were discussed and corresponding treatment measures were proposed.The main contents are as follows:（1）The single-factor evaluation method and Nemero index method are used to evaluate the water quality of the river.The single-factor evaluation method identifies the main water body categories of rivers as surface water type Ⅲ,Ⅳ type,Ⅴ type and inferior to type Ⅴ.Nemeiro index evaluation method divides rivers into good water quality group and poor water quality group.The good water quality group is mainly concentrated in summer in terms of time distribution,and mainly concentrated in the lower reaches of the river in terms of spatial distribution.The group with poor water quality is mainly concentrated in winter in terms of time distribution,and mainly distributed in the upper reaches of the river in terms of spatial distribution.（2）According to the similarity of water quality characteristics,the cluster analysis uses hierarchical clustering method to divide the 12 months into three groups.Among them,May to October is the wet season,January to April is the normal water season,and November to 12 is the dry season.At the same time,the 14 monitoring points are divided into three groups,of which the clean water quality group is the main tributary into the river,the poor water quality group is the upstream of the main stream,and the good water quality group is the middle and lower reaches of the main stream.In water quality monitoring,the monitoring point and monitoring time can be selected in three groups of time and space to optimize the monitoring point and reduce the frequency of monitoring.（3）Using principal component analysis and factor analysis to analyze the characteristics of pollution sources in the spatial system clustering results,the key factor loads in the principal components of the good water quality group are Oil,LAS,As,COD,Cr⁶⁺and Cu,which mainly represent industrial Source pollution,domestic source pollution and heavy metal pollution.the key factor loads in the main components of the poor water quality group are NH₃-N,Oil,pH,Hg,Cd,Se and VP,which mainly represent domestic source pollution and heavy metal pollution.Principal component analysis and factor analysis are used to analyze the characteristics of pollution sources on the results of time system clustering.The results show that for the group with poor water quality,the main pollution source in the wet and flat periods is the domestic source,and the main pollution source in the dry period is the industrial source.In the good water quality group,the main pollution source in the wet and flat water period is the industrial source,and the main pollution source in the dry period is the domestic source.（4）Based on the GM（1,1）model,an improved residual correction model was established,the accuracy of the model was tested,and the water quality prediction was realized on MATLAB.The Ma’andong section of the Xinmi section of the Shuangji River was selected as the predicted section,and five key factors were selected for model accuracy verification based on the results of pollution source analysis.The test results were all excellent,it shows that the residual correction GM（1,1）model can predict the water quality change of Shuangji River well.In addition,a 6-month water quality forecast analysis was carried out on the changes of the 5 key factors in the saddle hole section,and the corresponding reasons for the changes and preparation measures were explained.（5）After two years of field investigation along the river,visits to wading companies,monitoring and analysis of important sections of the river,and analysis of pollution sources,it is known that the causes of water pollution in the Xinmi section of the Shuangji River are mainly divided into domestic sewage pollution,industrial sewage pollution,domestic garbage pollution and river sediment pollution.According to the actual local conditions,five suggestions are put forward for the government to strengthen the attention to the improvement of surface water quality,give full play to the technical role of the expert team,strengthen the management of wading enterprises,strengthen the management of the river and strengthen the management of the sewage treatment plant.