Graduate Thesis Or Dissertation
 

Biodegradation of chlorinated methanes using a methylotrophic/anaerobic biofilm reactor

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  • Chlorinated low molecular weight solvents have been discovered in a number of the nation's groundwater supplies. Remediation of these aquifers will require some form of treatment. Presently, the dominant treatment method is air stripping which results in transfer of the solvent from the aqueous phase into the atmosphere. Biodegradation is an attractive alternative because the solvents can be converted into harmless by-products. This study explored the use of a combination of methylotrophic and anaerobic bacteria to biodegrade chlorinated methanes. The objectives were to develop a reactor system capable of sustaining both methylotrophic and anaerobic bacterial populations, and to evaluate the biodegradation of chlorinated methanes in this system. A gas permeable membrane (Goretex) separated the reactor into a liquid compartment and a gas compartment. The methylotrophs were provided methane as an electron donor and oxygen as an electron acceptor. Inorganic nutrients and chlorinated methanes were supplied in the bulk solution. Methane and chloromethanes were the sole sources of carbon supplied to the reactor. The membrane was rotated as a flat plate to ensure complete mixing and to encourage growth of a biofilm of uniform thickness. The methylotrophic bacteria were grown as a biofilm on a gas permeable membrane. The anaerobic bacteria appeared to grow both as a biofilm and in suspension in the bulk solution. The chlorinated methane concentrations were measured in the headspace, gas compartment, and liquid compartment. Oxygen and methane use was also monitored. The reactor was operated in batch mode, and the biofilm was assumed to be in a quasi-steady state condition with respect to growth. The combined methylotrophic/anaerobic biofilm system was effective in biodegrading carbon tetrachloride, chloroform, and dichioromethane. Carbon tetrachloride removal was accompanied by production of chloroform and trace amounts of dichloromethane, which is consistent with an anaerobic dechlorination pathway. Dichloromethane removal was inhibited in the absence of oxygen, which is consistent with a biological oxidation pathway. Chloroform removal under anoxic conditions was accompanied by production of dichloromethane, suggesting an anaerobic dechlorination pathway. Under aerobic conditions, the removal rate of chloroform increased nearly four fold, indicating that chloroform was biologically oxidized as well as anaerobically dechlorinated. Dechlorination of carbon tetrachloride and oxidation of dichioromethane occurred most rapidly, followed by combined dechlorination and oxidation of chloroform.
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file details CelesteStephenJ1990.pdf 2017-08-16 Pubblico Scaricare