The Fate of Polycyclic Aromatic Hydrocarbons Bound to Stormwater Pond Sediment During Composting

Recently, concentrations of polycyclc aromatic hydrocarbons (PAHs) that are above the Minnesota Pollution Control Agency's recommended limits for unrestricted use have been detected in stormwater pond sediments. Effective treatment methods are needed to remediate these PAH contaminated sediments to allow for unrestricted use and cost-effective disposal options. Based on the idea that PAHs in contaminated soil can be biodegraded when mixed with compost, this research sought to evaluate the effectiveness of using compost to biodegrade PAHs in contaminated sediment. Two benchtop experiments were performed that allowed for the simulation of the conditions in a compost pile that would favor biodegradation of PAHs bound to sediment. These experiments were able to effectively simulate the conditions of a compost pile and demonstrated that composting occurred as measured by carbon dioxide respiration, volatile solids content changes and temperature changes. Despite significant microbiological activity, only the three ring PAH phenanthrene, was found to be significantly degraded in all experiments. No PAH with four or more rings was found to be significantly degraded during the extent of composting. An assay that estimated bioavailability by measuring the desorption of PAHs from the contaminated sediment into the aqueous phase indicated that all but one PAH had a potentially bioavailable fraction. Since each PAH had a potentially bioavailable fraction, PAH biodegradation was likely limited both by a microbial community with only a small potential to degrade four to six ring PAHs and low aqueous PAH partitioning from the sediment.
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