Biodegradation of bicyclic and polycyclic aromatic hydrocarbons in anaerobic enrichments

Although many polycyclic aromatic hydrocarbons (PAHs) are known to be biode graded under aerobic conditions, most contaminated sediments are anaerobic. With recent results demonstrating that some bicyclics and PAHs can be degr aded without oxygen, information on specific biodegradation rates and elect ron acceptor stoichiometry is lacking. A fluidized bed reactor (FBR) enrich ment approach was used to enrich for bacteria from creosote-contaminated ma rine sediments with nitrate or sulfate as the sole potential terminal elect ron accepters and with naphthalene, biphenyl, dibenzofuran, and phenanthren e as the sole source of carbon and energy. Influent and effluent analysis s howed removal of naphthalene, biphenyl, and phenanthrene in the FBRs but no t dibenzofuran after 100-200 days. Batch incubations of FBR cells, using st rict anaerobic techniques, confirmed the transformation of naphthalene, bip henyl, and phenanthrene with stoichiometric removal of nitrate by the nitra te FBR enrichment. Similarly, phenanthrene, biphenyl,and naphthalene stimul ated sulfide production in the sulfate-reducing enrichment and were removed , generally with stoichiometric production of sulfide. The specific PAH bio degradation 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 remediati on of PAH-contaminated sediments.