| This research examined mechanisms of polyaromatic hydrocarbon (PAH) microbial remediation in superfund marine sediments (Eagle Harbor, Puget Sound) by studying a single representative compound---phenanthrene, a three-ring PAH, to frame the research questions and hypotheses. First, the studies determined estimates of the relative effects that environmental conditions and experimental methods had on the apparent, measured PAH biodegradation rate and extent in realistic settings including undisturbed marine sediment. Statistical analysis of published data led to a categorical model that quantified the influences of biodegradation 'ability' and PAH 'bioavailability' on the PAH biodegradation rates (accuracy within one order of magnitude). Second, analysis of the realistic phenanthrene biodegradation rate data in undisturbed marine sediments as a function of depth (0--10cm) established that the average first-order rate coefficients in Eagle Harbor sites were up to 0.0086 day-1 and surface sediments (0--1) often showed the highest biodegradation activities. Third, targeted controlled release materials were designed to support anaerobic biodegradation by sulfate and nitrate acting as electron acceptors. Two types of materials, nitrocellulose and calcium sulfate, were found to significantly enhance (factor of 2--3) PAH biodegradation rates in anaerobic marine sediments when measured by the whole core injection method. Fourth, two-dimensional models incorporating diffusion, sorption and Monod biodegradation were developed to analyze the measurement method, "whole core injection". The models quantified the influence of contaminant aging, indicators' maldistribution and smearing on the accuracy of measurement. Finally, by coupling both contaminant biodegradation and electron acceptor consumption processes, the models investigated the key factors (sorption, biodegradation rate, electron acceptor's concentration, inhibition effect, biodegradation stoichiometry and spacing of added electron acceptor) that control PAH biodegradation in undisturbed anaerobic sediments using dimensionless groups. By simulations, addition of controlled release nitrate (nitrocellulose) was illustrated as the most efficient way to accelerate in situ bioremediation of PAHs in heavily polluted Eagle Harbor sediment sites. Up to 35% of total PAH contaminant (300mg/L) was predicted to be removed within 5 years. |
