This thesis focused on using microcosms to better understand the aerobic cometabolic processes of TCE and cis-DCE transformation that occurred during a Cometabolic Air Sparging (CAS) demonstration at McClellan Air Force Base. The microcosms were created with groundwater and aquifer materials from the demonstration site. Concentrations of compounds in the microcosms were maintained to mimic conditions where the demonstration was performed. Propane was used as the primary substrate to stimulate indigenous propane-utilizers present in the McClellan subsurface. The microcosms were used to test the potential of the propane-utilizers to transform the CAHs of interest, and determine their nutrient requirements while transforming these compounds. Vadose zone microcosms were also created and used to compare the cometabolic processes and nutrient requirements of the propane-utilizers under these different conditions. After the addition of propane a ten-day lag period was observed before the propane-utilizers were stimulated in all the microcosms. The presence of CAHs and excess nitrogen did not have any effect on the lag period required to stimulate these microorganisms. Microcosms that received nitrogen amendments maintained effective transformation of TCE and c-DCE with successive additions. The rate of c-DCE transformation was observed to be faster than TCE transformation. Complete removal of the CAHs occurred in these microcosms. No other nutrients, such as phosphorous, were observed to cause any nutrient limitations. However, the microcosms that only had limited amounts of nitrogen present were only able to maintain transformation ability for a short time. Propane utilization rates gradually decreased with each addition, and CAH transformation eventually ceased. This was also observed during the CAS field demonstration after successive additions of propane. Ammonia gas was added to the sparge gas in the field and propane utilization and CAH transformation resumed. Ammonia gas was added to the nitrogen-limited microcosms, and like the field demonstration, propane utilization and CAH transformation resumed. Nitrogen was found to be a critical nutrient for effective cometabolism of CAHs. Nitrogen supplied either as ammonia or nitrate was required for the propane-utilizers to maintain effective rates of propane utilization and CAH transformation ability. By comparing different sets of microcosms under different conditions, estimates were made to the amount of nitrogen required by the propane-utilizers with and without CAHs transformed. The transformation of CAHs significantly increased the propane-utilizers requirements for nitrogen. A 2.0-3.8-fold increase in was observed for nitrogen consumption when CAHs were transformed, possibly resulting from toxic effects caused by the transformations. The sparge gas used at the CAS demonstration also contained ethylene at a low concentration (1% vol/vol). The microcosm experiments with this concentration of ethylene were found not to have any negative effects on CAH transformation. The propane-utilizers were also able to maintain propane utilization and CAH transformation at high CAH concentrations. The vadose zone microcosms showed that propane utilization in the vadose zone was an order of magnitude lower than what was observed in the saturated microcosms. Also bioavailable nitrogen was required to maintain propane utilization rates. However, higher CAH concentrations were found to inhibit the stimulation of the propane-utilizers under these conditions. / Graduation date: 2002

The 1,1-dichloroethene (1,1-DCE) cometabolic transformation abilities of indigenous and bioaugmented microorganisms were compared in microcosms constructed with groundwater and aquifer solids from the Moffett Field site, CA. Microbial community structure in the microcosms and possible community shifts due to 1,1-DCE transformation stress was evaluated by terminal restriction fragment length polymorphism method (T-RFLP). An existing biotransformation model was used to simulate the experimental data using parameter values determined by Kim et al. (2002) and Rungkamol (2001) with small adjustments to the parameter values. The laboratory microcosm studies showed that both indigenous and bioaugmented butane utilizers were capable of transforming 1,1-DCE when fed butane as a primary substrate. A butane-grown enriched culture was bioaugmented into the microcosms and exposed to several repeated additions of butane and/or 1,1-DCE, ranging from 7.1 to 76 ��mol and from 0.17 to 1.99 ��mol, respectively. The bioaugmented butane-utilizers showed a reduced lag period compared to the indigenous butane-utilizers. The greatest ability to transform 1,1-DCE was observed in bioaugmented microcosms, simultaneously exposed to butane and 1,1-DCE. Very little 1,1-DCE was transformed in the bioaugmented microcosms that were not fed butane, presumably due to lack of reductant supply and/or product toxicity of 1,1-DCE transformation. Microbial community analyses revealed similar results for replicate microcosms and differences in the community structure in microcosms subjected to different patterns of substrate addition and 1,1-DCE cometabolism. 1,1-DCE transformation resulted in temporal fluctuations in specific bacterial groups in the bioaugmented microcosms. It could be inferred that microorganisms, correlated with the T-RFL of 183 base pair (bp) were generally predominant in butane-fed bioaugmented microcosms simultaneously exposed to 1,1-DCE. Bioaugmented microcosms that were pre-exposed to 1,1-DCE for 29 days in the absence of growth substrate, followed by the addition of butane showed a significantly different microbial community from bioaugmented microcosms fed butane and 1,1-DCE simultaneously. Microorganisms with T-RFL of 179 or 277.8 bp dominated in these microcosms. These differences were possibly the result of extensive 1,1-DCE transformation product toxicity during the pre-exposure phase of the tests. A model developed by Kim et al. (2002) was used to mathematically describe the rate and extent of butane utilization and the cometabolic transformation of 1,1-DCE in the microcosm tests. Using the kinetic parameter values previously determined by Kim et al. (2002) and Rungkamol (2001), heuristic fits were obtained between the experimental data and model simulations. The model successfully predicted the trend of the butane utilization and 1,1-DCE transformation. The model outputs were statistically quantified for their fit to the experimental data by estimating Standard Error of Estimate (SEE). A reasonable fit between model predictions and experimental observations was achieved. A significant contribution of this study was developing the laboratory methods to evaluate the microbial abilities to cometabolize 1,1-DCE and determining the communities of microorganisms correlated with those biotransformation activities. Furthermore, the model comparison to experimental data indicated that there was a potential in using the existing model to predict and improve bioremediation strategies. The results showed the successful bioaugmentation of a butane-utilizing culture to improve transformation performance. / Graduation date: 2003