Graduation date: 1998

Batch microcosm studies were carried out to screen for microorganisms from the subsurface of Hanford DOE site that could cometabolically transform chloroform (CF) under aerobic conditions. The potential need for CF bioremediation at the Hanford site has resulted from the large release of carbon tetrachloride (CT) to the subsurface, of which a fraction anaerobically transformed to CF. Potential cometabolic substrates were screened for their ability to promote aerobic cometabolism of CF. The potential cometabolic substrates tested were isoprene, propene, octane, ammonia, methane, propane, and butane. Microcosms were constructed with 125 ml batch serum bottles filled with 25 g of aquifer solids, 50 ml of synthetic groundwater, and 60 ml of headspace air. Consumption of methane, butane, propane, and propene was slow, while the consumption of ammonia was very slow. Microorganisms stimulated on propene and octane showed no ability to transform CF. Limited CF was transformed in microcosms stimulated on ammonia and methane. Over 90% transformation of CF was observed in microcosms stimulated on either butane or propane during the initial incubation. Successive addition studies with methane, propane, and butane microcosms were conducted, because these substrates showed the most potential for driving CF cometabolism. The studies indicated that the most effective CF transformation was achieved by butane-utilizers. CF transformation was correlated with the consumption of the primary substrate. Propane- and butane-utilizers grown in the absence of CF showed transformation yields 3 times greater than those grown in the presence of CF. In butane fed microcosms, CF transformation was linked with butane and oxygen consumption, indicating that an oxygenase enzyme of the butane-utilizers was likely responsible for CF transformation. The butane-utilizers showed no ability to transform CT, which also suggests the possibility of CF transformation by an oxygenase enzyme. In butane microcosms, complete transformation of 55 pg of CF (1200 ��g/L of CF in aqueous solution) was observed. The maximum transformation yield of 0.03 g CF transformed/g substrates consumed was achieved by the butane-utilizers. A stoichiometric amount of chloride was released to solution from CF during CF transformation, indicating that complete dehalogenation of CF was achieved by butane-utilizers. In our knowledge, these were the first observations, demonstrating butane as a cometabolic substrate for CF transformation. / Graduation date: 1997