Modeling the role of partitioning substrates in DNAPL column studies
SABRE (Source Area BioREmediation) is a public/private consortium of twelve companies, two government agencies, and three research institutions whose charter is to determine if enhanced anaerobic bioremediation can result in effective and quantifiable treatment of chlorinated solvent DNAPL source areas. The focus of this 4-year, $5.7 million dollar research and development project is a field site in the United Kingdom containing a DNAPL source area with groundwater concentrations exceeding several hundred mg/L TCE. Prior to field evaluation, a significant program of laboratory and modelling studies are being conducted to better understand and predict system performance. An extensive microcosm study with site soil and groundwater revealed emulsified vegetable (soybean) oil (EVO) to be particularly effective at promoting reductive dechlorination in the presence of high TCE concentrations. One-dimensional column studies examined the influence of EVO on bioenhanced mass transfer, reductive dechlorination, and related processes influencing the overall biodegradation efficiency. Monitoring of a large suite of relevant breakdown products and geochemical parameters in both time and space in the column studies provided a rich data set relevant to the field site. This paper describes a parallel and coordinated numerical modeling effort at University of Edinburgh intended to simulate the experiments for the purpose of interpreting and better understanding the underlying processes. The biogeochemical process model considers numerous processes including the rate-limited dissolution of DNAPL and EVO, and the fermentation and dechlorination processes that regulate H2 (direct electron donor) availability. The model was calibrated to experimental results in order to provide base case parameters associated with the column systems. These simulations provide insight into the influence of EVO on dechlorination behaviour and toxic inhibition: A thorough sensitivity analysis is being conducted in order to illuminate the relative influence of key parameters such as extent of EVO slow release, rate of EVO fermentation, and degree of bioaugmentation on the fate of chlorinated ethenes.