Effects of oxidants on in situ treatment of a DNAPL source by nanoscale zero-valent iron: A field study

This study aimed to evaluate the efficiency of a nanoscale zero-valent iron (NZVI)-based treatment process for an aquifer contaminated with trichloroethylene (TCE) in which TCE in dense non-aqueous phase liquid (DNAPL) form was also present. The study further investigated the effects of site oxidants on the reactivity and lifetime of NZVI. The injection of 30 kg of NZVI into the site successfully removed 95.7% of TCE in the groundwater within the first 60 days without producing chlorinated intermediates. The chloride balance analysis estimated that 2214 g of TCE was removed and confirmed the presence of DNAPL TCE. The oxidation of NZVI particles by nitrate, dissolved oxygen (DO), and TCE consumed 29.5%, 13.5%, and 143% of the Fe(0) initially present, respectively, over 60 days. Thus, nitrate was identified as the priority among groundwater oxidants. The reactive lifetime of NZVI at the site was found to be at least 103 days, based on the monitoring of TCE, DO, and nitrate concentrations, oxidation-reduction potential (ORP), and the residual Fe(0) content of the NZVI particles. Solid samples that were retrieved from the site on the 165th day still contained substantial amounts of Fe(0), occupying up to 21.9% of the total mass, and retained considerable reactivities towards TCE. This indicates that the NZVI particles aged more than 5 months at the site can potentially be reused for TCE reduction even after extensive corrosion of Fe(0) has occurred. (C) 2016 Elsevier Ltd. All rights reserved.