Research On In-situ Chemical Remediation Of Black And Malodorous Urban River

With the accelerating process of urbanization in our country,more and more urban rivers are seriously polluted.Rivers are becoming black and malodorous,which has a serious impact on the surrounding environment.The black and malodorous river issue has become increasingly serious,and our country is gradually taking measures to harness the rivers.A lot of toxic and harmful pollutants were deposited in the black smelly river,which are released continuously to the overlying water.Therefore,the restoration of contaminated bottom sludge plays an important role in the governance of the black and malodorous rivers.How to choose a convenient and effective remediation technologies for polluted sediment to solve the black and malodorous rivers has become a key issue.Among many remediation technologies,in-situ chemical remediation technology has attracted more and more attention because of less investment,quick effect and easy operation.The black muddy sediment and overlying water in the urban river were chosen as experimental objects.A cylindrical reactor was made under laboratory conditions to simulate the actual environment of the river,and new compound chemicals and other chemical agents were added to the bottom sludge,to decide the appropriate dose of new compound agent,and to study the remediation effect of different medicaments and discover the remediation mechanism.On this basis,further research on the combined remediation effect of new compound chemicals and other methods will be conducted to find out more application directions for new compound agents.The conclusions in the experiments are as follows:(1)The addition of the new compound chemical has a remediation effect on bottom sludge and overlying water,and the positive effect increases with the increase of the dose of chemicals.The removal rates of bottom sludge AVS,TOC,overlying water COD,NH4+-N,and TP are respectively as high as 99.13%,36.00%,83.16%,80.47%,and 94.18%.When only this new compound chemical is considered to use to remediate bottom sludge,the optimum dosing amount is 16 g/L wet mud.When this dose of compound chemical is added in the experimental group,the bottom sludge AVS,TOC are respectively stable at 23mg/L,12.58g/kg,and the removal rates are respectively 98.63%,32.00%.At this time,the ORP values in the bottom sludge is stable at 15mv.The values of overlying water COD,overlying water NH4'-N and overlying water TP are respectively 20 mg/L,4.2 mg/L and 0.13 mg/L,and the removal rates reach respectively 75.61%,78.95%and 92.97%.At this time,the overlying water has a DO value of 6.01,and the pH value is 9.15.(2)Hydrogen peroxide is not suitable for the restoration of bottom sediment in black and malodorous rivers due to its characteristic of easy decomposition.The injection of calcium nitrate into the sediment leads to an increase of NH4+-N in the overlying water,while other chemical chemicals will reduce the concentration of NH4'-N.The precipitation of Ca-P is the major factor to control phosphorus pollution;the chemical containing Ca2+ has a better phosphorus removal performance than that without Ca2+.Ca(NO3)2 does not increase the DO concentration in the overlying water,while other chemical agents are able to elevate the DO more or less.Both the new compound chemical and calcium peroxide can increase the pH of overlying water,the new compound chemical has less negative effect from alkaline than that of calcium peroxide.Potassium hydrogen sulfate can reduce pH in overlying water,while calcium nitrate has little impact on the overlying water pH.The new compound chemical has better the removal performance of carbon,nitrogen and phosphorus than other agents,due to its good stability,less negative effect,better oxygen release ability and chemical oxidation.In situ chemical remediation of black and malodorous rivers,the new compound chemical has obvious advantages over other chemical agents.(3)The new joint remediation method by adding compound chemicals and water aeration,can further reduce the use of compound chemical dose to 10 g/L wet clay,and reduce the pH of the overlying water to 7.90 and reduce the content of NH4+-N in overlying water to 1.8 mg/L with the removal rate of 90.53%.Compared with the traditional method of pure aeration,this new joint remediation method reduces the aeration time,saves the economic costs,and improve the removal efficiency of pollutants.Overall,the most appropriate way to remediate the water is to add the compound chemical firstly and then aerate to the water.The AVS and TOC of the sediment remained are stable at 105 mg/L and 13.14g/kg with the removal rate of 94.17%and 94.17%respectively.The ORP of the sediment is-83 mv;the COD,NH4'-N and TP in overlying water remains stable at 21 mg/L,1.80 mg/L and 0.14 mg/L with the removal rate of 74.07%,90.53%and 92.63%respectively.The DO and pH values of the overlying water are respectively 8.40 mg/L and 7.90.(4)At the end of the experiment,the color of the sediment oxidized by the new compound chemical changes from black to brown,the transparency of the overlying water increases significantly and smell disappears.On the contrary,the color of the sediment was black and the overlying water smelled both in the control group.