Degradation Of Trichloroethylene In Aqueous Solution By Chelators-enchanced Fenton-like Reaction Of Magnetite

Water is one of the most important resources for human being.A large amount of refractory organic pollutants such as chlorinated olefins,halogenated hydrocarbons and phenols were discharged into water body,which has resulted in serious water pollution and posed a great threat to human health.Trichloroethylene(TCE)is one of the most common organic contaminations dectected in groundewater,which has been listed as a priority pollutants by many countries due to its obvious carcinogenic,teratogenic and mutagentic effects.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.Magnetite-catalyzed Fenton-like reaction is capable of generating highly reactive hydroxyl radical(HO·)at neutral pH,which could provide a new method for the treatment of TCE in grotmdwater.Firstly,the decomposition kinetics of hydrogen peroxide(H2O2)by magnetite was investigated in the present study.The results showed that the decomposition of H2O2 in magnetite/H2O2 aqueous solution followed the pseudo-first order reaction kinetics.In addition,the dosage and size of magnetite,the initial H2O2 concentration,PH value and the ionic strength of aqueous solution had significant impacts on the decomposition rate of H2O2.Moreover,the addition of a chelator,nitrilotriacetic acid(NTA),affecting the decomposition rate of H2O2 was compared under the same conditions.The results showed that the decomposition rate of H2O2 in magnetite-catalyzed Feanton-like reaction was efficiently enhanced by adding NTA.Secondly,the present study further investigated the effects of chelators such as NTA,ethylenediaminetetraacetic acid(EDTA),[S,S]-ethylenediaminedisuccinic acid(s,s-EDDS),malonate,citrate and phytic acid on the degradation kinetics of TCE and the decomposition kinetics of H2O2 in artifical groundwater by magnetite-catalyzed Fenton-like reaction at circumneutral pH.The results showed that the addition of NTA and EDTA effectively enhanced the degradation efficiency of TCE by magnetite-catalyzed Fenton-like reaction,while s,s-EDDS,malonate,citrate and phytic acid have minimal effects on TCE degradation.Through the free radical scavenging experiments,it was confirmed that TCE degradation by NTA enhanced Fenton-like reaction of magnetite was mainly caused by Ho·oxidation,and the superoxide anion radical(O2·-)contribution was less significant.It is noteworthy that the addition of NTA can reduce the usage of H2O2.Under the condations of 0.5 mM NTA,20 mM H2O2,0.1%?0.2%of magnetite(magnetite:sand,w/w),1:3 of solid-liquid ratio(sand:groundwater,w/w)and initial pH 7.8,the degradation efficiency of TCE reached 98.46%after 8 h of the reaction time and the rate constant of TCE degradation reached 0.526 h-1.The results of the present study can provide guidence for the treatment of TCE-contaminated groundwater,which has important theoretical and practical value.