The Biomec process for mechanochemically assisted biodegradation of PCBs in marine sediments

The Biomec process, a two-stage treatment based on a short mechanochemical (MC) pretreatment and then followed by an aerobic biological degradation, was developed and tested for detoxifying marine sediments that were largely contaminated by polychlorobiphenyls (PCBs). Clean marine sediment spiked with PCBs (Aroclor 1260) and, alternatively, with decachlorobiphenyl in slurry conditions was ultramilled for 1 min in a nutational high energy ball mill, then was treated aerobically in a bioreactor with a purposely selected commercial bacterium (Burkholderia xenovorans). With similar to 66 % overall PCB biodegradation achieved in less than 3 months, laboratory experiments confirmed the remarkable effectiveness of Biomec process when compared to direct bioremediation. The investigation showed in particular that the MC pretreatment decreased the chlorination degree of high-chlorinated PCB congeners, and consequently their biorecalcitrance, through the substitution of some chlorine atoms with hydroxyl groups. This reaction eases the aerobic degradation of the hydroxyl-substituted PCBs by B. xenovorans, allowing bacteria to skip the cell stressing step of aromatic ring bi-hydroxylation along the biodegradation pathway. After short MC treatment of the sediments, a common biological aerobic treatment can degrade PCB congeners, the highly chlorinated ones were included, in a fast, effective and cheap manner.