Recent laboratory and field studies have shown that injection of emulsified edible oils can provide an effective, low-cost alternative for stimulating anaerobic biodegradation processes. A pilot-scale permeable reactive bio-barrier (PRBB) was installed at a perchlorate and chlorinated solvent impacted site by injecting 380 L of commercially available emulsion (EOS® ) containing emulsified soybean oil, food-grade surfactants, lactate, and yeast extract through ten direct push injection wells over a two day period. Soil cores collected six months after emulsion injection indicate the oil was distributed up to 5 m downgradient of the injection wells. A previously developed emulsion transport model was used to simulate emulsion transport and retention using independently estimated model parameters. While there was considerable variability in the soil sampling results, the model simulations generally agreed with the observed oil distribution at the field site. Model sensitivity analyses indicate that increasing the injection flow rate or diluting the oil with more water will have little effect on final oil distribution in the aquifer. The only effective approach for enhancing the spread of emulsified oil away from the injection well appears to be injecting a greater mass of oil.
Recent research has shown that edible oils including soybean oil and hydrogenated soybean oil can be use to enhance the anaerobic biodegradation of a variety of contaminants including nitrate (Hunter, 2001; Lindow, 2004), perchlorate (Hunter, 2002), chlorinated solvents (Zenker et al., 2000; AFCEE and NFESC, 2004; Long and Borden, 2006; Borden and Rodriguez, 2006), TNT,
RDX and HMX (Fuller et al., 2004), acid mine drainage (Lindow and Borden, 2005) and chromium immobilization (Lindow, 2004). Because edible oils are relatively immobile and slowly biodegrade in most aquifers, a single, low-cost injection could provide sufficient carbon to drive reductive dechlorination for several years resulting in significantly lower operation and maintenance costs compared to aqueous-phase injection of soluble substrates (Harkness, 2000).
While edible oils appear to have many advantages for in situ anaerobic bioremediation, questions remain about the most effective approach for distribution of these fluids in the subsurface. Boulicault et al. (2000) describe the injection of neat soybean oil as a carbon source to stimulate in situ reductive dechlorination. However, other workers (Zenker et al., 2000; Lee et al.,2001) have reported difficulties in effectively distributing neat soybean oil without excessive permeability loss. This is supported by the laboratory studies of Coulibaly and Borden (2004) who found that injection of neat liquid soybean oil into sands resulted in high oil residual saturations with large permeability losses. In contrast, an oil-in-water emulsion with small, uniform droplets could easily be prepared using soybean oil and non-ionic surfactants approved for direct incorporation into food. Injection of this emulsion into sands with up to 10% clay resulted in much lower oil retention with low to moderate permeability loss (Coulibaly and Borden, 2004).