Decontamination of PCBs-containing soil using subcritical water extraction process

- The removal of PCBs from soil using subcritical water was investigated.
- PCBs were efficiently removed at 250 °C after 60 min of treatment.
- PCBs underwent partial degradation during the subcritical water extraction process.

Polychlorinated biphenyls (PCBs) are one of the excision compounds listed at the Stockholm convention in 2001. Although their use has been heavily restricted, PCBs can be found in some specific site-contaminated soils. Either removal or destruction is required prior to disposal. The subcritical water extraction (SCWE) of organic hazardous compounds from contaminated soils is a promising technique for hazardous waste contaminated-site cleanup. In this study, the removal of PCBs by the SCWE process was investigated. The effects of temperature and treatment time on removal efficiency have been determined. In the SCWE experiments, a removal percentage of 99.7% was obtained after 1 h of treatment at 250 °C. The mass removal efficiency of low-chlorinated species was higher than high-chlorinated congeners at lower temperatures, but it was oppositely observed at higher temperatures because the lower chlorinated congeners are formed by dechlorination of higher chlorinated congeners. Gas chromatography/mass spectrometry analysis confirmed that the PCBs underwent partial degradation. Several degradation products including mono- and di-chlorinated biphenyls, oxygen-containing aromatic compounds, and small-size hydrocarbons were identified in the effluent water, which were not initially present in the contaminated soil.