Degradation of trichloroethene by nanoscale zero-valent iron (nZVI) and nZVI activated persulfate in the absence and presence of EDTA

Abstract

This study investigated the degradation of trichloroethene (TCE) by nanoscale zero-valent iron (nZVI) w/o persulfate (PS) in the absence and presence of ethylenediaminetetraacetic acid (EDTA). In the absence of EDTA, the degradation of TCE obeyed the pseudo-first-order kinetics, and the rate constants increased exponentially with increasing molar ratio of PS and nZVI. Ethene was found to be the main reaction products in either the single nZVI system or nZVI/PS system. The presence of EDTA increased TCE degradation by nZVI in a short reaction period (within 360min), whereas the TCE degradation was almost ceased after 1day in a long-term (6days) experiment, resulting in a lower TCE degradation than that in the absence of EDTA. However, EDTA drastically decreased TCE degradation in nZVI/PS system. The positive effect of EDTA in the nZVI system should be attributed to its possible inhibition of the precipitation of Fe2+/Fe3+, which could reduce the surface passivation of nZVI. On the other hand, the adverse effect should be due to the rapid corrosion of nZVI by EDTA and the generation of a large amount of Fe2+ ions in short time, which could possibly lead to a rapid consumption of sulfate radicals originally for the degradation of TCE.