Analysis and solution of algae problems in drinking water sources in Zhuhai City
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Abstract:
The water supply system in Zhuhai City presents the characteristics of multiple water sources.The Xijiang River is the main drinking water source,and various reservoirs are auxiliary water sources.The reservoirs are responsible for the important function of water storage and water diversion.The water supply system combing the river and reservoirs in Zhuhai City makes the water quality not only affected by point and nonpoint source pollution in the river basin,but also interfered by the internal source pollution in the reservoir,which leads to the difficulty in controlling the stability of the water quality.The water quality of reservoirs in Zhuhai has gradually declined in recent years,and the algae content of the water body has continued to be high.The trend of eutrophication is becoming more and more obvious.However, there is still a lack of theoretical research into the impact of complex water supply system on algae in water sources,and technical guidance for algae control is therefore difficult and highly needed. The single factor analysis was used to compare the measured data and the regulated values of national standard,which aims to evaluate the water quality of four typical reservoirs (Meixi,Zhuyin,Dajingshan and Fenghuangshan reservoirs) in Zhuhai City from 2016 to 2019.The water quality characteristics and the spatial and temporal distribution of algae density in each reservoir were analyzed by the statistical method.The correlation between algae density and 10 water quality indexes (total nitrogen,total phosphorus,5-day biochemical oxygen demand,ammonianitrogen,total organic carbon,permanganate index,dissolved oxygen,2-methylisoborneol,geosmin,and turbidity) was studied by the bivariate analysis.The stepwise regression analysis was used to study and establish a regression model for preliminarily predicting the water quality of the reservoirs,with algae density,taste and odor compounds as dependent variables,and other environmental factors mentioned above as independent variables,respectively.Considering the current operational and problems of water plans in Zhuhai City, suitable solutions for solving the algae problems were analyzed and proposed from two perspectives: pollution source control and process transformation. The water quality of the reservoirs in Zhuhai City basically conformed to the standard of Class III surface water bodies from 2016 to 2019.However,the contents of total nitrogen and total phosphorus in some reservoirs exceeded the standard.From 2016 to 2019,the average algae density in the four reservoirs were 17.90 million cells/L in Meixi reservoir,18.78 million L-1in Zhuyin reservoir,9.43 million L-1in Fenghuangshan reservoir and 108.39 million L-1in Dajingshan reservoir,respectively.Under the influence of climate and water environment quality,the increase of algae density mostly occurred in spring,while the content of taste and odor compounds in the reservoirs were higher in autumn and winter,which could reach 5 times of the maximum odor threshold.Regression analysis showed that the water quality factors affecting algae density in Zhuhai reservoir involved total nitrogen and organic matter.The permanganate index was positively correlated with algal density,while total nitrogen and 5-day biochemical oxygen demand had negative correlation with the algal density.In addition,turbidity,organic matter and ammonianitrogen may contribute to the formation of taste and odor compounds in the reservoirs.And ammonianitrogen was the dominant factor and positively correlated with geosmin.Taking the monthly mean algae density of Zhuyin reservoir as the dependent variable while total nitrogen as the independent variable,a wellfitting regression model was established (R2=0.911,P<0.001,n=9).Furthermore,taking geosmin as the dependent variable while turbidity,permanganate index ammonianitrogen as the independent variables,a well-fitted regression model was developed (R2=0.911,P<0.001,n=54). High algae density,high taste and odor substances were the main water pollution problems in Zhuhai City.Ammonianitrogen and organic matter were the key factors affecting algae density and the production of taste and odor compounds in the reservoirs,algae problems in drinking water sources in Zhuhai City can be effectively solved by source control combined with the end treatment of ozone activated carbon or other advanced treatment technologies.
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