Degradation of PCB77 in spiked soils by ferrous sulfide-activated persulfate combined with potassium permanganate

Polychlorinated biphenyls (PCBs) in soil are difficult to remove by biodegradation, photodegradation and other conventional oxidation methods. This work tried to use FeS-activated persulfate (PS) combined with permanganate (KMnO4) to treat PCBs contaminated soil using 3,3′,4,4′-tetrachlorobiphenyl (PCB77) as a model pollutant. Compared with Fe0/PS and KMnO4/PS systems, the FeS/PS system showed a stronger degradation effect on PCB77. After reacting for 4 h in FeS/PS system, the addition of KMnO4 could increase the degradation efficiency of PCB77 from 50.27% to 79.20% in a total reaction time of 8 h. In FeS/PS/KMnO4 system, the degradation efficiency of PCB77 was directly proportional to the concentration of FeS, and greater amount of PCB77 was removed when more spiked soils were treated. Based on electron paramagnetic resonance (EPR) analysis and radical quenching experiments, •OH, SO4•-, 1O2 and O2•- were determined to play an important role in the oxidation of PCB77. Combined with identified intermediates and theoretical calculations, six main possible reaction pathways were proposed, including dechlorination, hydroxyl substitution, hydroxyl addition, sulfate substitution, sulfate addition, and C-C bridge bond cleavage. Acute toxicity and bioconcentration factors of intermediate products were predicted by T.E.S.T software, and the results showed that the ecotoxicity of PCB77 in soil was effectively reduced during the FeS/PS/KMnO4 treatment process. This work demonstrated that FeS/PS/KMnO4 system is applicable to treat PCB77 contaminated soil and has a great potential for soil remediation.