In-situ Treatment Of Trichloroethylene In Aquifer Media By Chelators-Regulated Fenton-like Reaction Of Magnetite

Groundwater is one of the most important freshwater resource for human existence.With the rapid development of industry and agriculture,a large number of organic pollutants were discharged into groundwater,which seriously polluted the groundwater environment.Trichloroethylene?TCE?is one of the most common organic contaminations dectected in groundewater,which has obvious carcinogenic,teratogenic and mutagentic effects and poses a great threat to ecological environment and human health.TCE in groundwater can not be efficiently removed by the traditional water treatment method.Thus,it is required to develop an effective technique for TCE removal in groundwater.The efficiency and mechanism of TCE degradation in aquifer media by chelatorsregulated Fenton-like reaction of magnetite were investigated in the present study through column experiments.Firstly,different concentrations of H₂O₂?1.0-100 m M?were added to C-1^C-3 to investigate the effect of H₂O₂ on TCE degradation at neutral p H.The results showed that with the increase of H₂O₂ dosage,the degradation efficiency of TCE in C-1^C-3 effluent increased gradually.Secondly,the effects of nitrilotriacetic acid?NTA?,[S,S]-ethylenediaminedisuccinic acid?s,s-EDDS?,ethylenediaminetetraacetic acid?EDTA?on TCE degradation in aquifer media by magnetite-catalyzed Fenton-like reaction were investigated.The results showed that the degradation effiencicy of TCE was enchanced by NTA-regulated Fenton-like reaction of magnetite,while the addition of EDDS had minimal effects on TCE degradation.The degradation efficiency of TCE by EDTA-regulated Fentonlike reaction of magnetite depended upon the content of magnetite.when the content of magnetite was high?e.g.,7 w.t.%?,adding EDTA could effectively enhance the degradation efficiency of TCE.While the addition of EDTA led to an inhibition of TCE degradation in sand column that with small dosage of magnetite?e.g.,0.5 w.t.%?.Moreover,the effect of hydraulic retention time?HRT?on TCE degradation efficiency during in-situ treatment was further investigated by changing the influent flow rates.The results showed that as the HRT of the column reactors was increased from 4 h to 24 h,the degradation efficiencies of TCE in C-2 and C-3 increased correspondingly.When the HRT was longer than 8 h,the degradation efficiency of TCE in C-2 bengan to exceed that in C-3.Therefore,when the content of magnetite is low,prolonging HRT could increase the degradation efficiency of TCE;While,when the content of magnetite is high,the effect of prolonging HRT on the degradation efficiency of TCE could be minimal.Furthermore,comparing the degradation efficiencies of TCE and the decomposition efficiencies of H₂O₂ during the column reactors running for 46-50,67-69,134-138,181-200 and 228-232 days,it was found that magnetite could maintain good stability and catalytic activity in the sand column reactor for a long period.The degradation products of TCE were also identified in the present study,and the results suggested that TCE was mainly degraded to formic acid and chloride ions.The present study further investigated the degradation efficiency of TCE in aquifer medium by homogeneous Fenton-like reaction with ferric ion complex(Fe^III-L).Firstly,the effects of H₂O₂ dosage on TCE degradation efficiency was studied.The results showed that an increase of H₂O₂ dosage?2.0-50 m M?led to the increase of the degradation efficiencies of TCE in Fe^III-NTA,Fe^III-EDDS and Fe^III-EDTA catalyzed Fenton-lik systems.Secondly,the effect of Fe^III-L concentration on the degradation of TCE in aquifer media was studied.The results showed that the degradation efficiencies of TCE increased greatly with the increase of Fe^III-L concentration from 0.02 m M to 0.2 m M.In addition,under the conditions of 10 m M H₂O₂ and 0.10 m M Fe^III-L,the effect of Mn²⁺ on the degradation efficiencies of TCE was further studied.The results showed that the addition of Mn²⁺?0.02-0.2 m M?could improve the degradation rates of TCE in the Fe^III-NTA and Fe^III-EDTA catalyzed Fenton-like systems,while the degradation of TCE was inhibted in Fe^III-EDDS EDTA catalyzed Fentonlike system in the presence of Mn²⁺.The present sutdy promoted the development of Fentonlike reaction with magnetite,which provided scientific basis and guidence for the in-situ remediation of TCE-contaminated groundwater.