Degradation of trichloroethylene in aqueous solution by persulfate activated with citric acid chelated ferrous ion

• TCE is frequently detected in groundwater with its recalcitrant characteristics.
• Effective degradation of TCE is achieved by CA–chelated-Fe(II) activated PS.
• SO4−, OH and O2− radicals are generated in CA–Fe(II)-activated PS system.
• Cl−, HCO3− anions and HA have an inhibitive effect on TCE degradation efficiency.

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 (SO4−), hydroxyl radicals (OH) and superoxide radical anions (O2−). 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 OH and 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.