Study of Sphingopyxis Isolates in Degradation of Polycyclic Aromatic Hydrocarbons

Phenenahtrene, anthracene and pyrene are polycyclic aromatic hydrocarbons (PAHs) which have been used in this study as model for degradation studies due to their relative toxicities. The ability of bacterial species isolated from a petrochemical wastewater in Iran, on degradation of polycyclic aromatic hydrocarbons was evaluated in aerobic batch aqueous system. Six isolates were selected from 12 by the best growth in phenanthrene. Optimum growth of the isolates on phenanthrene was achieved at 30 degrees C. Phenanthrene, anthracene and pyrene were used separately as sole carbon and energy source. Initial concentration, temperature and biodegradation time was selected as 100 mgL(-1), 30 degrees C, and 257 hours. Biodegradation yield of selected PAH, quantified by gas chromatography, revealed high phenanthrene degradation yield by all six bacterial species (i.e. up to 98%), while maximum 48% and 78% degradation was obtained for anthracene and pyrene, respectively. Phenanthrene was degraded to a greater extent than anthracene and pyrene by the isolates, possibly because it had been used as the sole carbon source during the earlier enrichment process. The results also show that enzymatic degradation of PAH depends on structural and thermodynamic characteristics of the compounds. The order of PAHs degradation by the bacterial species was: Phenanthrene>pyrene>anthracene. Biochemical studies showed all of the selected species were gram-negative, aerobic and nonfermentative bacillus.