A novel strategy using persulfate activated with thiosulfate for strong enhancement of trace 2,2′-dichlorobiphenyl removal: Influencing factors, and mechanisms

Efficient and environmentally friendly methods for the remediation of polychlorinated biphenyls (PCBs)-contaminated wastewater have become an important issue. In this study, persulfate (PS) was activated with sodium thiosulfate (TS) to degrade 2,2′-dichlorobiphenyl (DCB) at an extraordinarily high rate at pH ≤ 4.0 at room temperature. The PS/TS system exhibited much higher activity than systems with PS or TS alone at pH 2.0: 90.3% DCB was removed within 120 min, a much higher removal rate than those of the latter systems. Sulfate radical (SO₄⁻) was verified to be the main reactive substance through scavenging and trapping experiments; sulfate radicals can decompose and detoxify DCB by dechlorination and hydroxylation processes. The removal efficiency of DCB (58.5% in 120 min) was also satisfactory in the TS system, in which TS could perform nucleophilic substitution on the DCB molecule at pH ≤ 4.0, followed by DCB dechlorination and the generation of hydroxy-biphenyl. Plausible mechanisms and reaction pathways involving nucleophilic substitution in the TS system and the formation of reactive oxygen species (ROS) in the PS/TS system to attack the carbon atom on DCB were proposed and calculated by density functional theory (DFT). The presence of Cl⁻, NO₃⁻, HCO₃⁻ and humic acid (HA) may have inhibited the removal of DCB in the PS/TS system, while the effect was not significant in the TS system. Our work introduces novel and rapid removal methods for the removal of PCBs and may be significant for the development of efficient strategies for halogenated pollutant control in real water.