Fe3+-NTA-Catalyzed Homogenous Fenton-Like Degradation of Trichloroethylene in Groundwater at Natural pH (∼8.0): Efficacy, By-Products, and H2O2 Utilization

The ferric-nitrilotriacetate (Fe3+-NTA)-catalyzed homogenous Fenton-like reaction (i.e., Fe3+-NTA/H2O2) has received increasing interest for environmental applications, but its potential in degrading trichloroethylene (TCE) in groundwater still is not well known. The results of this study showed that Fe3+-NTA/H2O2 was more effective than other Fe3+-chelate/H2O2 processes (e.g., including ethylenediaminetetraacetate, ethylenediamine-N,N′-disuccinate, citrate, malonate, and tartrate) in degrading TCE in groundwater at natural pH (∼8.0). The effects of important parameters including the ratio of NTA∶Fe3+, and the dosages of Fe3+-NTA and H2O2 were investigated. Greater than 98% degradation efficiency of TCE in actual groundwater was obtained after 60 min of reaction time under the given conditions of NTA∶Fe3+=1.5∶1, 0.1 mM Fe3+-NTA, 5 mM H2O2, and pH 8.0. Hydroxyl radical (HO•) was responsible for the degradation of TCE, and the by-products were identified as formic acid and chloride ion (Cl−). Greater than 90% degradation efficiency of TCE in a sand column was achieved under dynamic conditions [0.5 mM Fe3+-NTA (1∶1.5), 4 mM H2O2, and hydraulic retention time of 4 h], resulting in stoichiometric ratios of ΔCl−∶ΔTCE and ΔTCE∶ΔH2O2 of ∼3∶1 and 4%, respectively. Compared with iron mineral (e.g., magnetite)-catalyzed Fenton-like processes, Fe3+-NTA/H2O2 led to much smaller consumption of H2O2 (at least 1 order of magnitude smaller). In addition, the buffering capacity of bicarbonate anions (HCO3−) in groundwater had a positive effect on the degradation of TCE by Fe3+-NTA/H2O2.