The mechanism and applicability of in situ oxidation of trichloroethylene with Fenton's reagent

Fenton's reagent is the result of reaction between hydrogen peroxide (H2O2) and ferrous iron (Fe2+), producing the hydroxyl radical ((OH)-O-.). The hy droxyl radical is a strong oxidant capable of oxidizing various organic com pounds. The mechanism of oxidizing trichloroethylene (TCE) in groundwater a nd soil slurries with Fenton's reagent and the feasibility of injecting Fen ton's reagent into a sandy aquifer were examined with bench-scale soil colu mn and batch experiment studies. Under batch experimental conditions and lo w pH values (similar to3), Fenton's reagent was able to oxidize 93-100% (by weight) of dissolved TCE in groundwater and 98-102% (by weight) of TCE in soil slurries. Hydrogen peroxide decomposed rapidly in the test soil medium in both batch and column experiments. Due to competition between H2O2 and TCE for hydroxyl radicals in the aqueous solutions and soil slurries, the p resence of TCE significantly decreased the degradation rate of H2O2 and was preferentially degraded by hydroxyl radicals. In the batch experiments, Fe nton's reagent was able to completely dechlorinate the aqueous-phase TCE wi th and without the presence of soil and no VOC intermediates or by-products were found in the oxidation process. In the soil column experiments, it wa s found that application of high concentrations of H2O2 with addition of no Fe2+ generated large quantities of gas in a short period of time, sparging about 70% of the dissolved TCE into the gaseous phase with little or no de tectable oxidation taking place. Fenton's reagent completely oxidized the d issolved phase TCE in the boil column experiment when TCE and Fenton's rege nt were simultaneously fed into the column. The results of this study showe d that the feasibility of injecting Fenton's reagent or H2O2 as a Fenton-ty pe oxidant into the subsurface is highly dependent on the soil oxidant dema nd (SOD), presence of sufficient quantities of ferrous iron in the applicat ion area, and the proximity of the injection area to the zone of high aqueo us concentration of the target contaminant. Also, it was found that in situ application of H2O2 could have a gas-sparging effect on the dissolved VOC in groundwater, requiring careful attention to the remedial system design. Published by Elsevier Science B.V.