Effect and mechanisms of pollutant removal in tetrachloroethylene contaminated water by persulfate-dithionite remediation system

Abstract

Tetrachloroethylene (PCE) is a common organic pollutant in industrial process, and the scope and extent of PCE pollution to groundwater are increasing in recent years. In this study, an emerging and effective method was used to purify PCE contaminated water by activating persulfate (PS) with dithionite (DTN). The addition ratio of PS and DTN were optimized in the removal of PCE by PS-DTN system and the optimal molar ratio of PS to DTN was 1 to 1 at the maximum PCE removal rate, and it was applicable in the pH range of 3–12. In PCE simulated wastewater, PCE removal rate in PS-DTN system exceeded 90% within 48 h, which was 66% higher than that in PS-NaOH system, and the degradation process followed pseudo-first-order kinetics with the reaction rate constant being 0.068 h−1. The dominant active species in PS-DTN system was proved to be sulfate radical on PCE degradation based on the radical quenching experiments and ESR analysis. HCO3− and low concentration of natural organic matter (NOM) could promote the removal of PCE, while Cl− and high NOM concentration had no adverse effect on PCE degradation. Few chlorinated intermediates (<2.77%) were produced and the dechlorination rate of PCE reached 95%, indicating a low secondary pollution risk. In simulated groundwater containing aquifer media, PS-DTN system could still degrade PCE to a certain extent, but the non-target reaction triggered by iron minerals on the medium mainly inhibited PCE degradation. The study showed that PS-DTN system was promising in degrading organic pollutants in groundwater.