Master of Science
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Sediment capping is currently considered one of the most convenient and efficient risk containment strategy for conatminated sediments. Conventional capping consists of placing one or more layers of inert materials on top of the contaminated sediment, retarding the flux of the pollutants to the water body and shielding the sediments from erosion or resuspension. The introduction of adsorbent materials promotes sequestration of the contaminants onto the capping media, but aging or leaks can affect the efficiency of such a reactive-cap. In a bioreactive capping, the use of an adsorbent material suitable for microbial colonization, facilitates both sequesteration and biodegradation of the contaminant. The aim of study is to experimentally evaluate the extent to which capping media selection affects bioactivity in model capping systems. Bench top laboratory studies investigated biological activity in model systems consisting of conventional capping materials (granular activated carbon [GAC], organoclay, and sand), mineral media, pore water extracted from contaminated sediments, electron acceptors (oxygen, nitrate, sulfate and iron) and the electron donor, naphthalene (a model polycyclic aromatic hydrocarbon). Microcosms were prepared and inoculated with microbial enrichements prepared with contaminated sediments collected from a river adjacent to a former manufactured gas plant. Concentrations of naphthalene and nahAc gene (encoding a dioxygenase associated with aerobic biotransformation of PAHs), were monitored for 100. Experimental data were collected and modeled; the relative kinetic rates were used to evaluate efficiencies of the different capping materials. Results suggest that GAC was the most efficient of the capping materials tested. Data showed that naphthalene concentration decreases only in oxic sediment-cap systems during the observation time, and naphthalene decay was statistically significant in oxic microcosms prepared with GAC. Abundance of the nahAc gene was sustained in oxic microcosms prepared with GAC and sand. Within oxic sediment-cap systems, a relationship between the naphthalene mass in solution and the gene copy numbers was observed in the microcosms prepared with activated carbon. This suggests that the nature of the capping material affected the interaction between abundance of a catabolic gene (nahAc) and concentration of the substrate (naphthalene).