Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation

This study investigates the degradation of trichloroethylene using advanced reduction processes (ARP), which was developed by combining activation methods and reducing agents to produce reactive reducing radicals that can destroy persistent oxidized contaminants. Screening experiments were performed using a combination of three reducing reagents (sulfite, sulfide, and dithionite) and three UV light sources (monochromatic light at 254 nm and two UV lamps with primary energy peaks at 365 and 312 nm, respectively). The screening test results showed that the highest TCE removal efficiency was obtained by the combination of sulfite with low-pressure UV light, monochromatic at 254 nm. The effectiveness of sulfite/UV-L ARP for dechlorinating TCE with regard to the initial TCE concentration, sulfite dose, solution pH, and light intensity was evaluated. Additionally, the reaction mechanisms and kinetics of TCE degradation were proposed. The photochemical degradation of TCE in ARP is attributed to sulfite radicals and hydrated electrons and generally followed first-order decay kinetics. At high pH and high sulfite dose, TCE was completely degraded, with chloride ions as the major reaction product. The TCE dechlorination rate constant increased as the sulfite dose, pH, and light intensity increased. This study provides the effectiveness of sulfite/UV-L ARP for TCE dechlorination and suggests optimum conditions that result in complete TCE conversion to a nonhazardous byproduct, chloride ions, and a rapid TCE dechlorination rate.