EFFECTS OF REDOX CONDITIONS AND COSUBSTRATES ON BIODEGRADATION OF PAH-CONTAMINATED MARINE SEDIMENT

摘要

Polycyclic aromatic hydrocarbons (PAHs) are a cause for concern due to their hazardous properties and recalcitrance. To facilitate cost-effective in-situ bioremediation of PAHs in the future, this study examined the potential of PAHs biodegradation in contaminated marine sediment by indigenous microbial consortia under three redox conditions: aerobic, sulfate reducing and denitrifying conditions using bench-scale reactor systems. Enhanced biodegradation under aerobic, denitrifying and sulfate reducing conditions promoted by the addition of the cosubstrates was also examined. Acetate and ethanol were used to stimulated anaerobic biodegradation while ethanol and salicylic acid were the cosubstrates in the aerobic studies. The effect on PAH biodegradation of facilitated solubilization by a nonionic surfactant, Triton X-100, was also evaluated in the aerobic experiments. The sediment used in this study was the PAH contaminated East River sediment collected near Rikers Island, NY. A critical factor in aerobic PAHs biodegradation in marine sediment is the availability of a sufficient supply of oxygen to overcome the initial oxygen depletion due to the high content of sulfide in the sediment. With sufficient oxygen, significant degradation of all 2-, 3-, 4- and 5- ring PAHs was achieved. Although lower ring compounds degraded faster than the higher ring PAHs, it was observed that those compounds present at higher initial concentration in the sediment exhibited higher degrees of degradation than those present at lower concentrations. This observation may be attributed to the bioavailability of these compounds in the aqueous phase. Nitrogen and phosphorus were present in sufficient quantities in this sediment to support biodegradation and additional supply of these nutrients did not accelerate biodegradation. In the presence of sulfate, PAHs degraded simultaneously with sulfate reduction, though the extent and rate of degradation was much lower than that observed under aerobic conditions. The addition of the cosubstrates ethanol and acetate under sulfate reducing conditions led to an enhancement of the rate of PAH biodegradation. Under denitrifying condition, no appreciable PAHs degradation was observed during an incubation period of 4 months, which may be attributed to an insufficient population of PAH degrading denitrifying organisms in the sediment. The immediate decrease in nitrate concentration, the simultaneous increase in sulfate concentration, and the production of nitrogen gas suggested the predominance of autotrophic denitrifying microorganisms in the sediment.