Feasibility of anaerobic biodegradation of PAHs in dredged river sediments

This report examines the anaerobic biodegradation potentials of PAHs in dredged river sediments under several redox environments. Batch biodegradation tests were conducted in bioslurry reactors containing sediment samples from Jones Island, WI. Tests with unamended sediments relied on PAH biodegradation by native bacteria utilizing background nutrients and electron donors and acceptors in the sediment. The amount of degradation of 15 PAH compounds found in the sediment, ranging from naphthalene to benzo(ghi)perylene, was measured. It was observed that all 15 PAH congeners biodegraded to some extent in unamended sediments. Acenaphthene showed the highest degradation at 79% disappearance. Indeno(123cd)pyrene showed the lowest at 8%. A general trend was observed with more disappearance in the lower molecular weight PAHs than the higher molecular weight PAHs. Addition of sulfate as an electron acceptor somewhat enhanced PAH biodegradation, whereas addition of nitrate did not. Induction of methanogenic conditions by adding dextrene (a simple sugar) did not appreciably enhance biodegradation of any of the 15 measured PAH congeners. It was speculated that the relatively high background sulfate levels, accompanied by sulfate-reducing bacteria native to the sediment may have played a significant role in effecting PAH biodegradation.