Feasibility Study of Thermal In Situ Bioremediation

A feasibility study of a new technology for remediating sites contaminated with dense non-aqueous-phase liquids (DNAPLs) is presented. The technology combines two conventional remediation approaches, thermal treatment and in situ bioremediation, in an effort to improve bioavailability through increased dissolution and biodegradation rates at elevated temperatures. To evaluate this new approach, a simulation model has been developed that combines expressions for first-order dissolution of immobile DNAPL spheres, dual-Monod biodegradation kinetics, and diffusion-limited desorption from soil micropores. The model is used to simulate remediation of a possible future contained release at a test cell at the Groundwater Remediation Field Laboratory at Dover Air Force Base in Dover, Del. Model simulations were conducted for temperatures ranging from 15 to 40°C using parameter values obtained from the literature. Simulation results show that, by increasing the temperature from 15 to 35°C, the amount of mass removed in the effluent (i.e., the amount of mass not degraded in situ) is predicted to be reduced by 94%, and the time required to reach the cleanup objective is predicted to be reduced by 70%. Parameter value sensitivity was also examined. Only those parameters that substantially reduced the biodegradation rates were found to have a strong influence on the predicted benefits associated with elevated temperatures. Based on the results of these modeling experiments, coupling of these two remediation techniques appears to hold considerable promise for sites contaminated with DNAPLs.