Remediation of polychlorinated biphenyls (PCBs) polluted soil using dielectric barrier discharge (DBD) plasma: Reactive nitrogen species (RNS) and produced dioxins

Abstract

Soil contaminated by PCBs from the electronic processing industries has attracted global concern because of their potentially persistent risks to human and ecological health. In this study, remediation of PCBs polluted soil using dielectric barrier discharge plasma (DBD) focused on 3,3′,4,4′-tetrachlorobiphenyl (PCB77) and 2,2′-dichlorobiphenyl (PCB4). About 90 % of PCB77 and PCB4 were degraded under input power of 120 W within 30 min. The carbon dioxide mineralization of PCB77 achieved at 18.2 % in 10 min treatment. Greater PCBs degradation was obtained with higher input power, lower moisture content, weaker acidity and presence of oxygenated gas. Increasing initial concentration of PCBs had no significant effect on PCB77 degradation, but contributed to PCB4 removal. PCBs degradation reactions were initiated by high-energy electrons. Reactive oxygen species (ROS) played major roles in PCBs degradation, which was also promoted by reactive nitrogen species (RNS) such as peroxynitrous radicals (HOONO). Multiple spectroscopies showed that chlorine radicals participated in PCBs degradation reactions. Chlorine substitution, ring-opening and bridge cleavage reactions were the main degradation pathways for PCB77. The production and re-degradation of trace dioxin-like substances ensured the safety of DBD use in the remediation of PCBs-contaminated soils.