Aerobic cometabolism of 1,1,1-trichloroethane and 1,1-dichloroethene by a bioaugmented butane-utilizing culture in a continuous flow column Public Deposited


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  • The transformation of 1,1,1 -trichioroethane (1,1,1 -TCA) and 1,1 -dichioroethene (1,1 - DCE) was evaluated in a continuous flow column reactor using a mixed culture that grew on butane. The column was packed with aquifer materials and groundwater obtained from the in-situ bioremediation test site at Moffett Field, CA. The pore volume of the column was 38 ml and the dispersion coefficient was 1.93E-3 cm²/sec, based on the results of the bromide transport experiment. The 1,1,1 -TCA transport test prior to biostimulation showed a retardation coefficient of 3.2. The inoculum for bioaugmentation was a butane-utilizing Rhodococcus Sp. culture used in the Moffett Field experiments. The total mass of cells added was 0.9 mg on a dry mass basis. Three days after bioaugmentation, with the continuous addition of dissolved butane, dissolved oxygen, and l,1,l-TCA (200 ug/L), decreases in all three of these solutes began. A maximum removal of 1,1,1 -TCA of 84% was achieved 10 days after bioaugmentation and remained fairly constant for a period of 20 days. The ratio of dissolved oxygen to butane consumption during this period was 4.5 mg O₂: 1 mg Butane. The influent concentration of 1,1,1 -TCA was then doubled, while dissolved oxygen and butane addition was maintained constant. The transformation of 1,1,1 -TCA during this period fluctuated between 24%-84%. Upon restoring the 1,1,1 -TCA concentration back to 200 ug/L the transformation stabilized at 59% removal. The butane-utilizers were then tested for their dependence on butane by turning the butane pulse off. The dissolved oxygen concentration doubled during this period and a residual transformation activity of 22% was observed. On restarting butane addition, 1,1,1 -TCA transformation of 69% was achieved. In the final phase, l,1-DCE was injected at 130 ug/L along with l,1,l-TCA, dissolved butane and oxygen. The butane-utilizing culture transformed 70% of 1,1 -DCE; however, the presence of 1,1 -DCE inhibited 1,1,1 -TCA transformation and approximately 50% of the butane injected was not consumed. The concentration of dissolved oxygen in the column also increased, which also indicating that 1,1 -DCE transformation inhibited butane and dissolved oxygen utilization and 1,1,1 -TCA transformation. Real-time PCR analysis conducted by Li (2004) indicated that during periods of low biotransformation of 1,1,1 -TCA, bioaugmented cell densities observed in the column effluent was high. This corresponded to a period of anoxic conditions, which may have caused cell detachment from the aquifer solids. The column reactor results were simulated using a combined biotransformationtransport model that uses MonodlMichaelis-Menten kinetics along with first-order sorption kinetics, to predict substrate utilization and chlorinated solvent transformation (Semprini and McCarty, 1992). The culture parameter values used to simulate biotransformation in the model were obtained from laboratory culture experiments conducted by Kim et al (2002) and Mathias (2002). Transport parameters (dispersion coefficient, porosity) were determined from modeling breakthrough test data with the CXTFIT2 transport model prior to bioaugmentation and biostimulation. Simulations of the colunm data using the transport and biotransformation parameters demonstrated that the model was able to simulate biotransformation of 1,1,1 -TCA fairly well. The model also indicated that 1,l-DCE transformation was toxic to the butane-utilizing culture and predicted the decreases in consumption of butane, and dissolved oxygen and in 1,1,1 - TCA transformation. This study showed that column experiments conducted on a small scale in a laboratory could be used to study the biotransformation capabilities of bioaugmented microorganisms. On the whole, the results suggest that the butane-utilizing culture could be successfully used in-situ for bioremediation, however transformation of mixtures of 1,1 -DCE and 1,1,1 -TCA could prove difficult.
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