NUMERICAL SIMULATIONS OF MICROBIAL GROWTH DURING AEROBIC BIOREMEDIATION

The effectiveness of natural or enhanced bioremediation strategies for contaminated groundwater often depends on the availability of electron acceptors such as dissolved oxygen. As the microbes grow and the degradation process evolves, the rate of contaminant mass loss can become severely limited by the depletion of electron-acceptors within the plume core. Replenishment from upgradient can be limited if a persistent source exists, for example a residual non-aqueous phase liquid (NAPL). In this scenario, microbial growth and contaminant degradation can become restricted to the outer periphery of the contaminant plume where dispersive mixing between substrate(s), electron acceptor(s) and nutrients will control the degradation rate. These 3D coupled processes must be well understood to develop efficient strategies involving oxygen or nutrient-enhanced remediation.

A 3D multi-component numerical model (BIONAPL3D) is used to visualize spatial patterns of microbial growth during passive and active bioremediation of gasoline and diesel fuel compounds. The simulations include dissolving multi-component NAPL sources into a 3D saturated groundwater system. Example cases are provided for a hypothetical spill of ethanol-enhanced gasoline, as well as for a pilot-scale tank experiment involving humic acid-enhanced remediation of diesel fuel. The model is used to show microbial response to various remedial strategies involving the addition of dissolved oxygen. The simulations show that the spatial variation of microbial growth can become a complex function of the flow system, source geometry, and electron acceptor distribution. The implications for remediation strategies are discussed.