A Comparative Study of Trichloroethylene (TCE) Degradation in Contaminated Groundwater (GW) and TCE-Spiked Deionised Water Using Zero Valent Iron (ZVI) Under Various Mass Transport Conditions

Abstract

The work reported here demonstrates that zero valent iron (ZVI), a material used in permeable reactive barriers, yields degradation rate constants for trichloroethylene (TCE) that are considerably different depending on whether they are determined in deionised water or in groundwater. Batch studies using ZVI and TCE-spiked deionised (DI) water and TCE-contaminated groundwater revealed that within 50 h, 80 % of the TCE present in groundwater was mineralised, compared to TCE-spiked deionised water in which only 50 % of TCE was demineralised by ZVI in 50 h. In both TCE-spiked groundwater and DI water, cis-dichloroethylene was the major by-product, and it was reduced together with TCE after 96 h of treatment. Along with changes in concentrations of TCE and its metabolites, increased levels of chloride confirmed TCE degradation. TCE-spiked groundwater gave a higher rate constant (k) under similar conditions. The elevated chloride (830 mg/l) concentrations of the groundwater could be a possible reason for this higher rate constant, in spite of the fact that groundwater also contains higher inorganic carbon (132 mg/l) and calcium (26 mg/l) and has a pH of 7.9. The rate constant (0.017–0.03223 h−1) and half-life of TCE (21.5 to 40 h) are within the reported ranges in the literature. The implications of the results for the performance of ZVI in permeable reactive barriers are that not only groundwater chemistry, but also groundwater flow conditions, plays a key role in TCE degradation.