Enhanced Reductive Dechlorination in Edible Oil Barriers -- Experimental and Modeling Results

Abstract

Recent laboratory and field studies have shown that injection of edible, food-grade oils can provide an effective, low-cost approach for stimulating reductive dechlorination in the subsurface. A biologically active Permeable Reactive Barrier (PRB) can be installed by injecting emulsified edible oils through a line of conventional wells or direct push points. Over time, the oils are slowly hydrolyzed by naturally occurring bacteria providing a slow-steady release of long-chain fatty acids to enhance the anaerobic biodegradation of contaminants migrating through the barrier. The concerns of this study are the lifetime of the emulsified oil injected, the average hydraulic retention time (HRT) needed for complete dechlorination, permeability loss, and if the process can be modeled. All materials used in the process are Generally Recognized As Safe (GRAS), food-grade materials to aid in gaining regulatory approval. O&M costs are expected to be low since the oils are expected to last up to five years between injections.

In this project, we evaluated the performance of edible oil barriers for stimulating reductive dechlorination by monitoring the performance of four laboratory columns (10 cm dia. by 100 cm long) that were continuously fed simulated groundwater with dissolved perchloroethene (PCE). Column 1 was treated with emulsified soybean oil and received an influent feed containing dilute HCl to inhibit biological activity. Column 2 was treated with emulsified oil only. Column 3 was treated with emulsified oil and anaerobic digester sludge to evaluate the effect of excess methane production on barrier performance. Column 4 received an influent solution containing lactate and yeast extract to evaluate the effect of soluble substrate addition on PCE degradation. All live columns were effective in stimulating reductive dechlorination of PCE. Complete conversion to ethene was enhanced by bioaugmenting the live columns with an enrichment culture of complete dechlorinators. Experimental results were then compared with numerical simulation results generated using the sequential first order decay module within the computer program RT3D to show if modeling the reductive dechlorination process was possible.