Guidelines for Effective Distribution of Emulsified Edible Oils

3D-39, in: A.R. Gavaskar and A.S.C. Chen (Eds.), Remediation of Chlorinated and Recalcitrant Compounds—2004. Proceedings of the Fourth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2004). ISBN 1-57477-145-0, published by Battelle Press, Columbus, OH, www.battelle.org/bookstore. GUIDELINES FOR EFFECTIVE DISTRIBUTION OF EMULSIFIED EDIBLE OILS Robert C. Borden and Kapo M. Coulibaly (North Carolina State University, Raleigh, NC, USA) Recent laboratory and field studies have shown that injection of Edible Oil Substrate (EOS) into the subsurface can provide an effective, low-cost alternative for the enhanced anaerobic bioremediation of chlorinated solvents, nitrate, perchlorate, acid mine drainage, and heavy metals. EOS is prepared from a mixture of rapidly biodegradable organic substrates, slowly biodegradable emulsified oils, and micronutrients selected to enhance reductive dechlorination. The oil-in-water emulsion is prepared to have small, uniform size oil droplets with a negative surface charge for ease of distribution under a variety of subsurface conditions. In this work, we present experimental and numerical modeling results demonstrating that emulsion transport and retention can be described using a standard colloidal transport model when the emulsified oil droplets are smaller than the sediment pores. The emulsion transport model was implemented as a user defined module within RT3D. All model parameters were determined independently measured in a series of 80-cm long laboratory columns packed with different types of clayey sand. The model was then validated by comparing model simulations with experimental results from two large (1 m x 1 m x 1 m) sandbox experiments. The model performed very well providing a close match between the simulated and observed oil distribution. The validated model was then used to identify emulsion injection system designs that provide effective treatment while minimizing costs. Design variables examined include: (1) injection flowrate; (2) emulsion concentration; (3) total amount of emulsion injected; and (4) chase water volume. Model simulations and experimental measurements indicate that emulsion droplets are very quickly captured by the solid matrix. Twenty-four hours after injection, the only organic material remaining in the aqueous phase are soluble organic substrates (e.g. lactate) added to provide rapid initial biodegradation of dissolved contaminants. The primary variables controlling the final oil distribution in the subsurface are: (a) oil ‘sorption’ capacity of the sediment; and (b) the amount of oil injected. To get the oil droplets to migrate farther through the aquifer, you need to inject more emulsion. The injection flow rate and initial emulsion concentration have no significant impact on the final oil distribution. Once the oil droplets are captured by the sediment surfaces, injection of additional chase water has no significant impact on the spatial distribution of the oil.