In this study, persulfate (PS) activated by the citric acid (CA)-chelated-ferrous ion (Fe(II)) to stimulate the oxidation of trichloroethylene (TCE) in groundwater remediation was investigated. The experimental results showed that TCE can be completely degraded over 60 min with a PS/Fe(II)/CA/TCE molar ratio of 15:2:1:1, demonstrating the effectiveness of Fe(II)-CA activated PS oxidation on TCE degradation. The probe compound tests clearly identified the generation and intensity of the reactive oxygen species in PS/Fe(II)/CA system, namely sulfate radicals (center dot SO4-), hydroxyl radicals (center dot OH) and superoxide radical anions (O-2(-center dot)). Moreover, the free radical quenching studies further indicated the generation of these reactive oxygen species and OH is the predominant one in Fe(II)-CA-activated PS system. The TCE degradation rate decreased as the Cl-, HCO3- anions and HA increased over the tested range of ion strengths, owing to their significant scavenging function to center dot OH and center dot SO4- radicals. Briefly, Fe(II)-CA activated PS oxidation is a highly promising technique for remediation of the contaminated sites containing TCE, but more complex constituents existed in in-situ groundwater should be carefully considered for its practical application. (C) 2014 Elsevier B.V. All rights reserved.