In-situ Remediation Of Aniline Contaminated Groundwater By Sodium Bisulfite Enhanced Potassium Permanganate

Aniline（AN）is an important intermediate in the chemical industry.It is widely used in the production of rubber,leather,plastics and petroleum.AN leakage accidents often occur during chemical production,storage and transportation,causing soil and groundwater pollution on the site.AN is highly toxic and carcinogenic,and is listed as an environmental organic pollutant that needs to be strictly controlled.According to relevant standards,the concentration limit of AN in our country’s water environment is below 0.1 mg/L.In addition,nitrobenzene（NB）polluted groundwater will also produce a large amount of AN under reducing conditions,which will be adsorbed in the aquifer medium and become a slow-release long-term pollution source.Therefore,there is an urgent need for new technologies that can treat AN pollution in a long-term effect.This topic used sodium bisulfite（NaHSO₃）to enhance potassium permanganate（KMnO₄）to degrade AN polluted groundwater.Through batch experiments,the factors affecting the degradation of AN were explored,and the reaction conditions were optimized in combination with response surface methodology.A set of in-situ remediation equipment was set up to simulate groundwater pollution and remediation,and to investigate the degradation effect of NaHSO₃ and KMnO₄ on AN and the effluent index under in-situ injection.Sustained-release materials based on NaHSO₃ and KMnO₄ were prepared with cements such as paraffin wax and stearic acid,and the release characteristics of the active ingredients in the sustained-release materials were investigated.Set up a permeable reaction barrier（PRB）simulation experiment device based on slow-release NaHSO₃ and KMnO₄ to investigate the remediation effect of PRB filled with NaHSO₃/KMnO₄ sustained-release capsules and sustained-release columns on aniline-contaminated groundwater,and monitor TOC,Eh,acute toxicity and other effluents Indicators,explored the production of trivalent manganese,identify the degradation products in the reaction system,and formed a technology for remediation of groundwater contaminated by aniline based on the combined slow-release oxidant of KMnO₄ and NaHSO₃.The following main conclusions were obtained:1)NaHSO₃ can significantly enhance the degradation rate of AN by KMn O_4.The removal rate of AN is linearly positively correlated with KMnO₄ dosage,NaHSO₃ dosage and reaction time,and linearly negatively correlated with the initial p H of the solution.The response surface experiment found that when the KMnO₄/NaHSO₃/AN（substance ratio）was 20/13/1,the initial p H=5,and the reaction time was 10 min,the simulated value of AN removal rate was 99.76%,which was similar to the result of the verification experiment.The results of in-situ injection experiments showed that the degradation rate of AN reached 100%after PM-BS-PP treatment,the TOC degradation rate of the solution effluent reached 80%,the redox potential was high,there was strong oxidant in the solution,and the acute toxicity experiment found that the injection mixture The water sample of the solution was highly toxic,and the toxicity mainly came from the residual agent.GC-MS analysis of the solution sample found that the intermediate product of AN degradation was mainly phenol,which eventually turned into a ring-shaped long paraffin.2)Stearic acid was used as a cementing agent to prepare PM and SB sustained-release capsules based on KMnO₄ and NaHSO₃.The release rate of the active substances in the sustained-release capsules gradually decreased with time,and the release rate of NaHSO₃ was significantly higher than that of KMnO₄.After adding montmorillonite,the release of KMnO₄ and NaHSO₃ were uniform,and the sustained-release effects were good.In the AN degradation experiment,the capsule with PM/SB/montmorillonite stearic acid=3/1/1/6 had the best degradation effect on AN,when the rate was 0.4 mg/L and AN influent concentration was 100 mg/L,the AN removal rate was always 100%.The SEM image showed that the release reaction of KMnO₄ and NaHSO₃ in the capsule creates pores,which was conducive to the release reaction of internal active substances.The UV spectrum scan found that the solution had an absorption peak at 258 nm,and the absorbance gradually increased and stabilized at 3.94,indicating that highly active Mn（Ⅲ）continued to exist in the solution.In the simulated AN leakage experiment,3/1/1/6 capsules can effectively remove AN under AN leakage.After 12 hours,the AN concentration remained below 1 mg/L,and the AN removal rate is above90%.The TOC concentration of the effluent of the solution was reduced,and the oxidation-reduction potential was high,stabled at 410 m V.The acute toxicity experiment found that the total toxicity of the effluent and the residual toxicity of the agent were high,and there were residual oxidants in the source of toxicity in the effluent.3)Paraffin wax was used as a cementing agent,and KMnO₄and NaHSO₃ were used as active ingredients to prepare sustained-release paraffin columns to study release rules and in-situ remediation effects on AN-contaminated groundwater.The results showed that the release rate of active substances in PM-PRB and SB-PRB gradually decreased with time,and the release rate and cumulative release percentage of NaHSO₃were higher than that of KMnO₄.The release rate of the active substance in the paraffin column was lower than the release rate of the capsule.The removal rate of AN by SB/PM-PRB was higher than that of PM-PRB alone.When the influent AN concentration was 25 mg/L and the flow rate was 0.1 m L/min,the AN removal remained above 99%within 96 h.Fourier transform infrared spectroscopy analysis showed that the PRB components did not change significantly before and after the reaction,indicating that the stability was good.The results of UV-vis scanning showed that the intensity of the characteristic peaks of AN and benzene ring decreased significantly,indicating that SB/PM-PRB can open the benzene ring and destroy the amino structure of AN.In-situ simulation experiments have found that the use of SB/PM-PRB can effectively degrade AN.The high redox potential indicated that the effluent was highly oxidative.The TOC measurement found that there were other organic products after the degradation of AN.4)Using NaHSO₃ to activate KMnO₄ to produce high-activity slow-release trivalent manganese,the slow-release trivalent manganese was applied to groundwater pollution treatment,and different methods are selected for in-situ remediation.For contaminated sites with a large number of AN leaks,it was suitable to choose the method of in-situ injection of chemical remediation agents,which can completely degrade the high concentration of AN,thoroughly mineralized the AN,and reached the goal of environmental pollution treatment in our country;for long-term groundwater AN pollution sources,it was suitable for selecting the permeable reaction grid for in-situ repair treatment.The filled slow-release materials can release active substances for a long time,effectively degrade AN in groundwater,and meet the economic and environmental benefits of actual site restoration.