Study On Remediation Of Chlorinated Organics Contaminated Groundwater By Nano Zero-Valent Iron And Organic Acids

Chlorinated organic compounds are commonly used as chemical intermediates and organic solvents.Some chlorinated organic compounds have the characteristics of high density,low water solubility,not easy to degrade,strong toxicity,which are common pollutants left over from chemical sites and one of the difficulties in site environmental remediation.In this paper,combined with part of the key special project of the Ministry of Science and Technology(No.2019YFC1805802),the groundwater samples of chlorinated organic pollutants in the original pesticide and solvent production enterprises were selected,and nano zero-valent iron(nZVI),biochemical fulvic acid(BFA)and citric acid(CA)were used as remediation agents to explore the removal effect of chlorinated organic pollutants,in order to provide reference for remediation of chlorinated organic pollution in groundwater.Three groundwater well samples with different pollution levels were selected,and the initial concentrations of chlorinated organic compounds were 8.20×10~5、5.25×10~3、2.94×10~3μg/L.The main research conclusions are as follows:1.Removal effect of different chemicals on chlorinated organic matter in groundwater:(1)The reaction equilibrium of each chemical was basically reached at 1day,and the nZVI reaction was in accordance with the quasi first order reaction kinetics;(2)1 g/L BFA,CA,nZVI removal effect were the best,5 h removal rate was 70.77%-85.17%、75.19%-80.43%and 77.17%-86.64%,respectively.When the dosage increased to 10 g/L,the removal efficiency of nZVI did not increase significantly,but decreased to a certain extent;(3)The removal efficiency of nZVI was the best.The higher the initial concentration of chlorinated organic compounds,the more prominent the removal effect of nZVI.2.Removal of chlorinated organic compounds in groundwater by combined dosing of chemicals:(1)The reaction was in accordance with the quasi first order kinetics,and reached equilibrium in 5 h;(2)The results showed that CA/nZVI combination had a better effect on the removal of chlorinated organic pollutants in high and medium concentration groundwater,and BFA/nZVI combination had a better effect on the removal of chlorinated organic pollutants in low concentration groundwater;(3)When the mass ratio of BFA/nZVI and CA/nZVI was 1:2,the removal efficiency was the best;(4)Compared with the single dosage,the fitting reaction time of the combined dosage was significantly reduced.However,the effect of the combined agent on the removal of chlorinated organic pollutants in high concentration groundwater was not significantly improved,and the removal rate of chlorinated organic pollutants in medium and low concentration groundwater samples was up to 32.44%.The experimental results combined with relevant literature analysis:(1)nZVI has high surface activity and good removal effect for chlorinated organic pollutants.However,when the amount of nZVI was too much,it might cause agglomeration,reduce the specific surface area and affect the removal efficiency;(2)The main reason that BFA/nZVI can improve the removal efficiency wass that the reduced BFA can transfer its own electrons to chlorinated organics and promote the dechlorination reaction;(3)The combined addition of CA and nZVI can maintain the solubility of Fe and chelate with Fe,improve the stability of nZVI and effectively promote the removal of chlorinated organic matter.In summary,in the remediation of high-depth chlorinated organic pollution in groundwater,it is necessary to carry out sufficient simulation experiments to determine the appropriate dosage.Excessive dosage of chemicals will not significantly improve the remediation effect,and the appropriate dosage of groundwater remediation in the experimental site was 1 g/L.CA/nZVI combination was more suitable for remediation of chlorinated organic matter in high and medium concentration groundwater,BFA/nZVI combination was more suitable for removal of chlorinated organic matter in low concentration groundwater.In practical application,different reagents should be selected by stages according to the change of the concentration of chlorinated organic pollutants in groundwater to improve the removal effect of pollutants.