A statistical approach to understanding microcosm methods for microbially mediated dechlorination of trichloroethene in bedrock aquifers

Publication Year:
2007
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Repository URL:
https://scholars.unh.edu/dissertation/370
Author(s):
Druschel, Stephen J
Tags:
Engineering; Civil; Environmental; Environmental Sciences
thesis / dissertation description
Microcosms were evaluated using statistical methods to advance the measurement and characterization abilities for in situ reductive dechlorination of trichloroethene (TCE) in fractured rock aquifers. Microcosms constructed with unincubated crushed rock in groundwater provided the best microcosm model of in situ TCE degradation, when prepared and incubated to simulate the in situ environment. Microcosms constructed with only groundwater were effective at modeling the TCE degradation only when the microcosms were amended with (total) organic carbon (TOC). Incubation of crushed rock core within the residual TCE plume caused a substantial decline in TCE degradation for biotic intrinsic microcosms, suggesting an effect that is inhibitory to TCE degrading microbes. Glass beads were found to be an inadequate substitute for rock media because their corrosion (i.e., hydrolysis and ion exchange) increased pH and dissolved oxygen beyond in situ ranges. Addition of incubated granular material to sterilized groundwater provided insufficient microbial population or metabolic activity in the microcosms to achieve TCE degradation.The ability of microcosms to discern slow rates of TCE degradation was evaluated, with specific application to bedrock aquifers. A method was developed to determine whether TCE biodegradation is occurring, assuming first order kinetics, and to estimate what is the longest half-life (i.e., the smallest biodegradation rate) that can be predicted by microcosm experiments for a reasonable incubation period, an acceptable statistical confidence and the fewest replicates when evaluating natural attenuation of TCE in fractured bedrock aquifers.A factorial experiment of biostimulated anaerobic TCE dechlorination in fractured bedrock aquifers using microcosms evaluated several potential biostimulants (i.e., nutrients, vitamins, sterile groundwater). Optimum TCE degradation occurred with biotic crushed rock microcosms with sterile groundwater that resupplied in situ nutrients to the microcosm.The procedures and methods developed in this study substantially enhance the ability to evaluate biotic fate of TCE in fractured rock aquifers, providing an effective approach for remedial design at low to moderate cost.