Laboratory Assessment of a Screening Model: Exploring the Coupling between Dissolution and Degradation Rates in Ganglia-Dominated Source Zones

Abstract:

In-situ bioremediation is a widely applied treatment technology for source zones contaminated with dense non-aqueous phase liquids (DNAPLs). It is both economical and reasonably efficient for long-term management and closure of contaminated sites. A number of laboratory studies have demonstrated enhancement in chlorinated ethene dissolution rates due to the presence of dehalogenating microorganisms, which may lead to increased mass removal rates and shorter cleanup times. Previous modeling efforts have suggested this dissolution enhancement can be a factor of 10 or more when the contaminant is located in high saturation DNAPL pools. Yet, laboratory studies with DNAPL trapped as ganglia have suggested dissolution enhancement is often less than 10. This presentation investigates the interplay between dissolution and degradation rates in ganglia-contaminated source zones using a one-dimensional, simplified, steady-state, analytical solution to the advection-dispersion-reaction equation. A linear driving force model is employed to simulate ganglia dissolution. Degradation kinetics are approximated as zero- or first-order. Model predictions are independently compared to laboratory data available in the literature. Results indicate that dissolution enhancement predictions in ganglia-dominated source zones are often much less than those predicted assuming high saturation pools, suggesting that the presented model is a better tool for estimating bioenhanced dissolution in ganglia-contaminated regions. Furthermore, this screening model provides a remarkably good prediction of laboratory results and could provide practitioners with a useful tool for estimating the extent to which bioenhanced dissolution may aid in site closure strategies.