Biological treatment of transformer oil using commercial mixtures of microorganisms

The biodegradation of six PCB congeners (IUPAC nos. 28, 52, 101, 138, 153, and 168) present in transformer oil using different commercial mixtures of microorganisms (Sybron 1000, Biozyn 301, Biozyn 300, DBC 5, ChZR, NS 20-10, NS 20-20, and NS 20) under anoxic, oxic, or anoxic/oxic treatments was investigated at laboratory scale. Overall, PCB congener biodegradation was observed in all treatments in the ranges of 0–99%, 2–97% and 40–94% under anoxic, oxic, or anoxic/oxic treatments, respectively. The highest biodegradation of total PCB congeners occurred using Sybron under oxic and anoxic conditions (76.0% and 91.3% reduction, respectively; initial PCB concentration, 1417.1 mg l−1). Also, the highest biodegradation extent of the PCB congeners occurred when the commercially available mixture of microorganisms, Sybron, was used (84.7% reduction) under combined anoxic/oxic conditions. Demonstration that biodegradation of most of the individual PCB congeners was achieved by the commercial mixtures of microorganisms in this study suggests that PCB-impacted environments can sustain populations of these PCB-metabolizing organisms. This is particularly relevant for the development of biostimulation or bioaugmentation strategies for the bioremediation of PCB-contaminated wastes.