Study On The Reactivity Toward Trichloroethylene In Groundwater,Toxicity And Mobility Of Sufidated Nano Zero-valent Iron

Groundwater remediation has been a hot issue in the field of environmental geochemistry.Trichloroethylene(TCE)is one of the priority control pollutants in groundwater due to its high toxicity,hard degradation,and high detection rate in groundwater.Nano zero-valent iron in-situ injection technology was recently developed to address this problem.Here,a systematic study of sulfidated nano zero-valent iron(S-nZVI)was conducted,especially on the reactivity towards TCE,cytotoxicity and transport capacity of S-nZVI.Thereby,carboxymethyl cellulose(CMC)coated S-nZVI was proposed and experimentally confirmed to show better properties in groundwater remediation.The results indicates that S-nZVI has the Fe(0)core-FeS shell structure.FeS shows good stability and conductivity,which can protect electron source and accelerate electron transfer.Thus S-ZVI shows higher reactivity towards TCE than nZVI.The degradation activity of S-nZVI is related to the S/Fe molar ratio.When Fe/S=15,which is the optimal ratio,the reaction rate constant of S-nZVI was maximum to be 7 times that of nZVI.The degradation of TCE is restrained by the complex hydrochemical conditions of groundwater to some of the degree,such as natural organic matter,dissolved oxygen,inorganic ions,pH and temperature.Fortunately,the influence on the reactivity of S-nZVI is far less than that on nZVI that the former still shows good degradation efficiency with the change of groundwater composition and environmental conditions.After sulfidation,S-nZVI shows relatively lower cytotoxicity to E.coli than nZVI,but still sterilize.However,due to the ubiquitous presence of natural organic matters in groundwater,direct contact between S-nZVI and cells can be avoided and toxicity is greatly reduced.Therefore,the cytotoxicity of S-nZVI in the environment do not need to be concerned.The particle size and aggregation effect of S-nZVI are also inhibited compared with nZVI,but the increase of dispersion is not enough to make it transport in saturated quartz sand column.In order to enhance the mobility of S-nZVI in the underground aquifer and thus transport to the target area,to remove pollutants,carboxymethyl cellulose(CMC)is used as a stabilizer to for S-nZVI coating and CMC@S-nZVI is thus obtained.The dispersion stability is significantly improved after modification,and CMC@S-nZVI can effectively transport in saturated quartz sand column.The transport ability of CMC@S-nZVI increases with the increase of S/Fe,initial concentration of CMC and solution viscosity.The adsorption of co-existing heavy metals such as Cr(VI),As(V),Cu2+in environment influence the dispersion stability and transport of CMC@S-nZVI,which reduces the possibility of secondary pollution caused by the transfer of nano iron loaded with heavy metals.CMC coating has a slight inhibitory effect on the degradation of TCE,which is enhanced with the increase of the dose of CMC.However,even if the concentration of CMC reaches 1 g C/L,CMC@S-nZVI(2 g/L)also can degrade 90%of TCE(0.1 mM)within 16 h.Therefore,CMC@S-nZVI performs with both good reactivity and transport capacity,which could be better applied in-situ groundwater remediation.