Remediation of polychlorinated biphenyl-contaminated soil by soil washing and subsequent TiO2 photocatalytic degradation

An efficient method was developed for treating polychlorinated biphenyl (PCB)-contaminated soil by soil washing and subsequent TiO2 photocatalytic degradation, and the photocatalytic degradation mechanism of PCBs was explored. Hydroxypropyl-beta-cyclodextrin (HPI'CD) and polyoxyethylene lauryl ether (Brij35) were used to extract PCBs from contaminated soil at first, and then the degradation of PCBs in the soil extracts was performed by TiO2 photocatalysis under UV irradiation. Washing conditions including washing time, the concentration of HPI'CD/Brij35, and the ratio of soil mass to solution volume for extracting 2,4,4'-trichlorobiphenyl (PCB28) from a PCB28-spiked soil were investigated at first. The results indicated that both HPI'CD and Brij35 exhibited good performance. The intermediates of photocatalytic degradation of PCB28 were from its dechlorination and hydroxylation in the HPCD and aqueous solutions, respectively. A field PCB-contaminated soil from e-waste recycling sites was treated by this method. The results showed that the extracting percentage was significantly affected by the chlorination degree of PCBs, and HPI'CD slowed down the photocatalytic degradation efficiency of overall PCBs. Soil washing and subsequent TiO2 photocatalytic degradation was successfully applied for treating PCB-contaminated soil, and HPI'CD strongly altered the pathways of the photocatalytic degradation of PCBs.