FEASIBILITY OF PAH BIODEGRADATION IN CONTAMINATED MARINE SEDIMENT UNDER AEROBIC AND SULFATE REDUCING CONDITIONS

PAHs have been shown to be very persistent in the environment, though their biodegradation in aerobic and anaerobic environments has been reported. Most published studies were conducted by spiking PAH free media with PAH compounds, and biodegradation was often tested by adding PAH - degrading pure cultures or enrichments. In this study the feasibility of PAH biodegradation under aerobic and sulfate reducing conditions by indigenous microorganisms present in the aged PAH-contaminated sediment was examined. The sediment was collected from the East River near Rikers Island, NY. The possibility of enhancing biodegradation by providing supplemental nutrients (N and P) to the aerobic studies, and by repeatedly adding ethanol or acetic acid as cosubstrate to the sulfate reducing studies was investigated. Sediment and overlaying seawater were used to prepare the sediment-water microcosms, with the sediment serving as the source of both the media containing PAH substrates and the microbial inoculum. Initial oxygen uptake for the aerobic biodegradation experiment was evaluated using respirometery. The results were used to establish a protocol for oxygen resupply to avoid oxygen depletion during the course of the experiment. With sufficient oxygen present, considerable degradation of the 2-, 3-, 4- and 5- ring PAHs was observed. Supplementing the N and P nutrients did not improve biodegradation, indicating that there was a sufficient supply of these nutrients already in the sediment. Under sulfate reducing conditions, phenanthrene was degraded while the sulfate concentration decreased appreciably. Phenanthrene removal was enhanced significantly by repeated addition of ethanol or acetic acid as cosubstrates. This may be due to the growth of phenanthrene – degrading organisms, and/or the stimulated cometabolism of phenanthrene. The phenanthrene-degrading sulfate reducing bacteria (SRB) did not appear to metabolize other PAHs, even those with a smaller number of benzene rings. The results of this study could be valuable for bioremediation of PAH-contaminated sediment.