Pyrene biodegradation by free and immobilized cells of Mycobacterium frederiksbergense using a solvent encapsulated system

Polycyclic aromatic hydrocarbons (PAHs) are classified as hazardous pollutants in the environment due to their toxic, mutagenic and recalcitrant nature. Compared to other methods, biodegradation using microorganisms seems to be attractive alternative for treating PAH contaminated environment. However, there are limitations because of its low aqueous solubility and negligible bioavailability to the degrading microbes. The present study investigated biodegradation of pyrene, a model PAH compound, using both free and calcium alginate immobilized cells of Mycobacterium frederiksbergense. To overcome the bioavailability problem, organic phase (silicone oil) containing the PAH compound was encapsulated using chitosan coated sodium alginate-polyvinyl alcohol beads for subsequent use in the biodegradation experiments. Prior to the biodegradation experiments, characterization of the silicone oil encapsulated beads and the cell immobilized beads were also performed. In pyrene biodegradation experiments using the free cells, following an initial lag phase of 4 d, ~90% degradation was achieved at 400 and 800 mg/L initial pyrene concentrations. On the other hand, immobilized cells in beads of ~700 μm size showed better performance even at a very high initial concentration of 2000 mg/L.