Biodegradation of bicyclic and polycyclic aromatic hydrocarbons in anaerobic enrichments

Although many polycyclic aromatic hydrocarbons (PAHs) are known to be biodegraded under aerobic conditions, most contaminated sediments are anaerobic. With recent results demonstrating that some bicyclics and PAHs can be degraded without oxygen, information on specific biodegradation rates and electron acceptor stoichiometry is lacking. A fluidized bed reactor (FBR) enrichment approach was used to enrich for bacteria from creosote-contaminated marine sediments with nitrate or sulfate as the sole potential terminal electron acceptors and with naphthalene, biphenyl, dibenzofuran, and phenanthrene as the sole source of carbon and energy. Influent and effluent analysis showed removal of naphthalene, biphenyl, and phenanthrene in the FBRs but not dibenzofuran after 100-200 days. Batch incubations of FBR cells, using strict anaerobic techniques, confirmed the transformation of naphthalene, biphenyl, and phenanthrene with stoichiometric removal of nitrate by the nitrate FBR enrichment. Similarly, phenanthrene, biphenyl, and naphthalene stimulated sulfide production in the sulfate-reducing enrichment and were removed, generally with stoichiometric production of sulfide. The specific PAH biodegradation rates in these cultures were 1-2 orders of magnitude lower than those reported for aerobic cultures. These results show that bicyclics and PAHs can be biodegraded under nitrate- and sulfate-reducing conditions and suggest that anaerobic treatment may provide a useful option for remediation of PAH-contaminated sediments.