Browsing by Subject "Biological degradation"
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Item Bioavailability of trichloroethylene adsorbed to activated carbon(2021-12-03) Miller, Kenzie McCreery; Werth, Charles J.Powder Activated Carbon (PAC) is being injected into contaminated groundwater aquifers to retard chlorinated ethene plume migration. There is some evidence that PAC can also enhance chlorinated ethene biodegradation rates in groundwater, but there is no consensus. The purpose of this study was to evaluate relative rates of diffusion and biological degradation of TCE on PAC to determine which process limits overall transformation rates. For this purpose, a commercial PAC called COGACTM was used, and sorption isotherms, desorption kinetic profiles, and biodegradation rates of trichloroethene (TCE) were measured. The isotherm results for adsorption of TCE on COGACTM are similar to that of other activated carbons found in literature. The Freundlich adsorption model provided a better fit of the data than the Langmuir model, and Freundlich constants of 2009 (μg/g)(L/μg) [superscript 1/n] and 0.481 were determined for K [subscript F] and 1/n, respectively. Diffusion rate constant values ranging from 0.288 1/day to 24.48 1/day were found for TCE desorption from PAC. Greater agreement was found between the simulated and experimental results for the fraction of mass remaining than the flux. More confidence is placed in the higher value because greater mass balance errors are associated with the lower diffusion rate constant value. Biological degradation experiments were variable, and the most favorable experiments produced TCE degradation rate constants ranging from 2.962 to 3.258 μmol/L/day in the presence of PAC. These values were used to calculate Damköhler (D [alpha]) numbers and values <<1 were obtained. For these conditions, the rate of diffusion is between 8 and 800 times greater than the rate of TCE biodegradation, suggesting that the system is limited by biological reductive dechlorination rates of TCE and not diffusion from the PAC. These results are applicable to the specific conditions of this work and caution is advised when extending them to other conditions not tested