Impact Of Reclaimed Water Irrigation On Shallow Groundwater Quality And Risk Assessmenton

The unification of social and environmental benefits.Based on a large number of domestic and foreign related literatures,based on the full understanding of the status of reclaimed water irrigation in the study area,combined with the surface water,soil and groundwater environment in the study area,the main research on the total nitrogen?TN?and total pollutants in the reclaimed water in the project area.10pollutants such as phosphorus?TP?,ammonia nitrogen?NH₃-N?,COD_Cr,copper?Cu?,cadmium?Cd?,lead?Pb?,zinc?Zn?,chromium?Cr?,and mercury?Hg?in reclaimed water The change of pollutant content in the transport channel;the effect of pollutants on the soil and shallow groundwater quality after one year of irrigation using the reclaimed water;predicting the impact of pollutants on shallow groundwater under reclaimed water irrigation for five consecutive years in the study area and The pollution index method carries out a risk assessment of the forecast results.The main conclusions are as follows:?1?The surface water environment of the study area and the water environment of the reclaimed water transport channel basically meet the Class III water standard of the surface water environmental quality standard.After the reclaimed water is discharged through the sewage outlet and transported through the transport channel,the pollutants TN,TP,NH₃-N and COD_Crr increase slightly with the increase of the transport distance,and reach a stable value at 500m from the sewage outlet;heavy metals Cu,Cd,Pb,The pollutant content of the six indicators of Zn,Cr and Hg is generally lower with the distance from the sewage outlet.The lower the pollutant content,the stability is reached at 400m from the sewage outlet;the reclaimed water will not cause the water quality of the Kui River after entering the Kui River system.Negative Effects.?2?Through the investigation of surface water,groundwater and soil environment in the test area,the surface water quality of the test area is good,and basically meets the Class III water standard of surface water environmental quality standard.The groundwater quality meets the Class III water quality standards of the Groundwater Environmental Quality Standard?GB-T14848-2017?.The main type of soil is yellow soil,the lithology is sandy and sticky,and the permeability coefficient is0.01¹m/d,which is suitable for reclaimed water irrigation.?3?After one year of reclaimed water irrigation test field,the pollutants mainly accumulate in the soil 0-15cm,and the content of each pollutant in the 0-15cm soil has a small Increase compared with the background value.Except Cd,the pollutants TN,TP,NH3-The contents of N,Cu,Pb,Zn,Cr and Hg are lower than the sCreening values of soil pollution risk in agricultural land?others?.The soil surface content of Cd exceeds the soil pollution risk sCreening value of agricultural land?others?,but its content is far.It is far lower than the agricultural pollution risk control value?other?3.0mg/kg.The pollutants are mainly concentrated in the soil surface layer?0-15cm?.With the Increaseof soil depth,the content of each pollutant is drastically reduced.The removal rate of soil pollutants TP,TN and ammonia nitrogen in the aerated zone at 60cm is 85%and 78%,respectively.84%.Soil and soil water at 60 cm were not affected by pollutants TP,TN,ammonia nitrogen,CODCr and heavy metals Cu,Cd,Pb,Zn,Cr and Hg.Compared with well water irrigation,the soil surface TP and TN content Increase d significantly,inCreasing by 24.7%and 20%respectively,which is more conducive to Crop growth from an agricultural perspective.?4?It was found that the leachate of the reclaimed water irrigated soil column met the groundwater III quality standard by simulating the one-year reclaimed water irrigated soil column percolation test.The content of each pollutant in the leachate deCreased as a whole with the Increaseof the percolation amount,and finally stabilized,and the final detection value was far below the standard value.The inflection point appeared at 30cm.The pollutants did not penetrate the 60cm soil aerated zone and did not enter the groundwater depth of 12m,which had no adverse effect on the quality of shallow groundwater.Through the single factor evaluation method,it is concluded that one year of reclaimed water irrigation will not Increase the content of heavy metals such as Cu,Cd,Pb,Zn,Cr and Hg in groundwater.?5?It is known that the content of various pollutants in leachate under the condition of continuous irrigation of reclaimed water for five years through reclaimed water leaching soil column experiments shows that the five-year reclaimed water simulates irrigation,the pollutant content in leachate is relatively stable,and the total nitrogen of pollutants?The content of TN?,total phosphorus?TP?,CODCr,ammonia nitrogen?NH3-N?,zinc?Zn?,chromium?Cr?,and mercury?Hg?is negative compared with the Increasein the background value of well water.However,long-term reclaimed water irrigation may cause a slight Increase in the content of groundwater pollutants Cu,Cd and Pb in the study area,but will not affect the groundwater quality in the study area.Through the comprehensive pollution index method using multiple pollutant indicators,the risk assessment of five-year reclaimed water irrigated soil is carried out.The comprehensive pollution index PI of the five-year reclaimed water simulated irrigation leachate is smaller than the groundwater background value pollution index PI,which will not cause groundwater pollutionin the study area.