The Treatment Of Tetrachloroethylene Contaminated Groundwater Using Percarbonate Catalyzed With Iron And Modified Iron

The chlorinated solvents are widely used as chemical materials,organic solvents and product intermediates in chemical,electronics,pharmaceuticals,print and dry cleaning industries.As a result of the wide use and improper operation during production,storage,transportation and application,disposable of wastewater,or leakage from storage tanks,chlorinated solvents have been one of the most common pollutants in the soil and groundwater in China.In consideration of the universality in groundwater/soil and the perniciousness to human body,tetrachloroethylene(PCE)is chosen as the target contaminants in this study.Sodium percarbonate(SPC)is used as the oxidant.Chelating agents(CAs)and reducing agents(RAs)for ferrous iron(Fe(?))and ferric iron(Fe(?))are employed to alleviate or overcome the drawbacks of Fe(?)or Fe(?)catalyzed SPC system in chlorinated solvents contaminated groundwater remediation.The effects of process parameters,such as the concentration of Fe(?)/Fe(?),SPC,various chelating agents or reducing agents on PCE degradation performances were investigated in Fe(?)/Fe(?)catalyzed SPC systems.The reactive oxygen species generated in the above mentioned processes were also identified through the free radical probe tests and the free radical scavenger experiments.The effects of real groundwater matrix such as common inorganic anions(Cl-and HCO3-ions),and natural organic matter(NOM)on PCE degradation were also thoroughly investigated.Through the above researches,the main results are listed below:PCE could be effectively degraded in Fe(?)/SPC system.PCE was degraded rapidly in the initial 1 minute and then slowed down sharply.However,PCE degradation in Fe(?)/SPC system could be well fitted to the pseudo-first-order kinetic model with the degradation rate significantly lower than that of Fe(?)/SPC system.The free radical probe test,free radical scavenger experiments and EPR detection results showed that HO' free radical oxidation was the main mechanism for PCE degradation in Fe(?)/SPC system,and the effect of O2·-free radical was negligible.In Fe(III)/SPC system,the contribution of HO' free radical was about 90%and O2·-free radical made a minor contribution.The measured Cl-concentration was highly consistent to PCE degradation rate(>98%)and no other products were detected after the reaction,which indicated that PCE was completely dechlorinated in both systems.The end products of PCE degradation were deduced to be H2O and CO2.In CIT or OA modified Fe(II)/SPC systems,PCE degradation was significantly enhanced with less iron precipitation observed.In Fe(?)/SPC system,CIT,OA and Glu could significantly increase the PCE degradation rate and accelerative effects could be ranked in an ascending order of CIT>Glu>OA in Fe(?)/SPC system.The degradation of PCE in Fe(?)/SPC system was significantly lower than that in Fe(?)/SPC system.Excessive chelating agents made negative impacts on PCE degradation in both Fe(?)/SPC and Fe(?)/SPC systems.In CIT or OA modified Fe(?)/SPC systems,the contribution of HO· free radical for PCE degradation were reduced to over 80%,while the contribution of O2·-free radical increased slightly to less than 20%.In CIT,OA or Glu modified Fe(?)/SPC system,the contribution of HO' free radical for PCE degradation was close to 90%.The dechlorinate results showed that PCE could be completely dechlorinated in all the above mentioned systems.The addition of HAH significantly enhanced the PCE degradation in Fe(?)/SPC system.Similar accelerative phenomenon were also observed in Fe(?)/SPC system with the addition of HAH,SS ASC and the accelerative effects could be ranked in an ascending order of:SS<ASC<HAH.After adding the reducing agent,the measured Fe(?)concentration was significantly increased in Fe(?)/SPC system,showing that the reducing agents significantly enhanced Fe(?)reduction.Excessive HAH,SS or ASC were unfavorable in both Fe(?)/SPC and Fe(?)/SPC systems.In HAH/Fe(?)/SPC system,the contribution of HO· and O2·-free radicals for PCE degradation were about 80%and 20%respectively.The contribution of HO·free radical in HAH,SS or ASC modified Fe(?)/SPC systems were all about 90%,while O2·-free radical was less than 20%.Cl-release rates after reaction in HAH/Fe(?)/SPC system and HAH,SS or ASC modified Fe(?)/SPC were highly consistent to PCE degradation,and no other products were detected in the above mentioned systems,indicating that PCE could be completely dechlorinated in all the above systems.The real groundwater had inhibitory effects on PCE degradation in Fe(?)/SPC and Fe(?)/SPC systems.Both Cl-and HCO3-anions had inhibitory effects on PCE removal in Fe(?)/SPC and Fe(?)/SPC systems,and the addition of CIT and HAH could alleviate the phenomenon and accelerate PCE degradation.In addition,NOM had a similar effect as the anions in inhibition of PCE degradation in Fe(?)/SPC system.However,NOM slightly accelerated PCE degradation in Fe(?)/SPC system.No significant effect on PCE degradation was observed with the addition of NOM in CIT or HAH modified Fe(?)/SPC and Fe(?)/SPC systems.