Photodecomposition of PCBs absorbed on sediment and industrial waste: implications for photocatalytic treatment of contaminated solids

PCBs in contaminated sediment and soil have been photodegraded in slurry suspension with TiO2 and simulated solar illumination without pre-treatment or amendments. Degradation of 81% of the PCBs in St. Lawrence River sediment was achieved in a 24 h irradiation period. Replicate experiments using five times as much sediment and half the light intensity yielded similar results. The observed degradation rates of individual PCB congeners correspond with gas chromatograph retention time and chlorine number. Lesser and ortho chlorinated PCBs are preferentially photodecomposed. The solubility of individual congeners controls the observed rate of decomposition by regulation of the transfer of PCBs to the aqueous phase and thus effectively retards access to the catalyst (anatase). The rate and degree of photodegradation can be enhanced by the use of lower wavelength ultraviolet light which leads to hydroxylation of PCB congeners increasing solubility and accessibility to photocatalytic reactions. Photodecomposition of PCBs in a slurry composed of furnace ash, core sands, and aluminum-rich (>45% Al2O3) slag from an aluminum foundry was increased from 45 to 88% during a 24 h irradiation period by using low wattage UVC lamps instead of solar equivalent illumination.