The primary objective of this study was to investigate the use of hydrogen as a structural substitute or as a reducing equivalent in the anaerobic biodegradation of methanol, methyl tert-butyl ether (MTBE), toluene, phenol, and 2,4- dichlorophenol. In addition, biodegradation rates of these compounds at various initial concentrations with and without inhibition of sulfate reducing bacteria were determined along with anaerobic biodegradation rate constants for each of the compounds studied. Rates of methanol biodegradation were only slightly altered in molybdate amended microcosms indicating that methanol is a noncompetitive substrate in Blacksburg soil. MTBE biodegradation was slow and followed first order kinetics with respect to initial concentration. Molybdate had no affect on MTBE biodegradation alone, but increased the biodegradation rate in MTBE microcosms which were amended with ethanol. Toluene, phenol, and 2,4-dichlorophenol biodegradation proceeded at two different rate versus initial concentration relationships for lower and upper concentration ranges. Phenol biodegradation followed first order kinetics. The 2,4-dichlorophenol biodegradation rate order varied from 0.78 to 1.75. Monod kinetics were followed by methanol, toluene, and phenol, but not by MTBE, ethanol amended MTBE, or 2,4-dichlorophenol. Addition of molybdate to inhibit sulfate reduction increased the degradation rates more for compounds which may require hydrogen in a structural position (2,4-dichlorophenol, MTBE) than those which require hydrogen for proton reduction (methanol). Biodegradation or recalcitrant compounds may be stimulated by the addition of organics (such as ethanol) which produce hydrogen upon biodegradation. / Master of Science

The objective of this study was to determine the potential for biodegradation in subsurface soils and groundwater from sites in Williamsport, PA, Wayland, NY, and Dumfries, VA. These subsurface systems were characterized both physically, chemically and biologically. Bacterial populations were substantial in all systems and ranged from 10³ to 10⁸ colony forming units per gram. Soil sampling was done in a quality-controlled aseptic manner using conventional drilling end sampling equipment. A matrix of test-tube microcosms was used to determine biodegradation rates of methanol and t-butyl alcohol at concentrations ranging from 1 to 1000 mg/L. Methanol degraded readily at all sites ranging from 0.8 mg/L/day to 20.4 mg/L/day and rates were generally greater in the saturated zone. TBA biodegraded at all sites, but was refractory in nature. Biodegradation rates for TBA in anaerobic subsurface systems were found to increase directly with initial concentration from 10⁻⁴ mg/L/day for 1 mg/L to 10⁻¹ mg/L/day for 80 mg/L. TBA biodegradation in the aerobic system was essentially constant over all concentrations. Biokinetic coefficients were determined for methanol and TBA at each site based on plots of utilization rates versus substrate concentration and reciprocal plots of these values. The K values found suggest that aerobic subsurface systems can utilize alcohols at a greater rate than anoxic subsurface systems and can be used for comparative purposes. The K_s of anoxic subsurface systems were found to be large due to the low temperature (10°C) found in aquifers. The results indicate that methanol contamination in groundwater has much less associated risk to drinking water supplies due to the ease of biodegradation. However, TBA poses a much greater risk due to the very slow removal rates at low concentrations, which could result in a residual level for over a decade in some cases. / Ph. D.

Current use of alcohols as neat automotive fuels or as inexpensive octane enhancers in gasoline-alcohol blends, in addition to their uses as solvents and starting materials in manufacturing, have created a concern due to the increased potential for groundwater contamination. Adsorption and water solubility are primarily responsible for separating gasoline-alcohol blend components in soils and would allow alcohols to move ahead of the remaining gasoline components (e.g., benzene). The presence of alcohols would be difficult to detect, and levels hazardous to humans or animals could be reached readily. The primary objective of this study was to investigate the use of a ¹⁴C-tracer technique for evaluation of subsurface biodegradation of groundwater contaminants. A modification of the heterotrophic activity assay, the radiorespirometric method, was employed as the ¹⁴C-tracer technique. The microorganisms used were those present in soil sampled aseptically at locations in Pennsylvania and Virginia. Both saturated and unsaturated zone soils were used. The alcohols used were methanol and tertiary-butanol. Methanol was easily degraded under both aerobic and anoxic conditions up to approximately 3000 mg/L. Tertiary-butanol was degraded very slowly under both aerobic and anoxic/anaerobic conditions, and an inhibitory concentration was not readily apparent. Tertiary-butanol was degraded at rates approximately 10² slower than methano1. The data generated in this study compare favorably with data obtained by oxygen-uptake and static-microcosm methodologies. / Master of Science / incomplete_metadata