Bioavailability of PCBs in biphasic bioreactors

Polychlorinated biphenyls (PCBs) are xenobiotic and toxic contaminants of soil and sediment. A possible remediation scheme involves solvent extraction followed by microbial biodegradation in biphasic bioreactors. This study examined the effect of two water immiscible liquid phases on the extent and rate of aerobic Aroclor® 1242 biodegradation by Burkholderia xenovorans LB400 under controlled conditions. The immiscible phases were neither toxic nor biodegradable by the employed organism and it was found that reduced aqueous phase availability, caused by the immiscible phases, had a negative effect on the extent and rate of degradation. The initial PCB concentration in the immiscible phase and the nature of the immiscible phase was shown to influence biodegradation. It was further found that under the employed conditions, providing intensive mixing, the microbial degradation rate and not the mass transfer of PCBs from the immiscible phase into the aqueous phase was limiting the degradation process. Despite reduced specific microbial degradation rates in the presence of a water immiscible phase a maximum volumetric degradation rate of 0.44 mg l−1 h−1 in the presence of 0.1% silicone oil could be achieved. The findings in the study show that microbial degradation of PCBs in biphasic bioreactors might be a suitable technology for the treatment of solvent extracts of contaminated soils.