Enhanced anaerobic bioremediation is being considered for remediation of a wide variety of groundwater contaminants, including chlorinated solvents, perchlorate, explosives, chromate, and certain radionuclides. One of the most common approaches involves injecting a soluble, readily biodegradable substrate. Soluble substrates, however, require frequent reinjection, which increases operating costs and can lead to biofouling of injection wells. At many sites, emulsified oils are being used to stimulate anaerobic biodegradation. The emulsified oils are relatively easy to inject in most aquifers and provide a long-lasting electron donor.
The overall objective of this project was to improve the understanding of how emulsified oils are transported in aquifers and the impact of these oils on contaminant biodegradation. Specific objectives included: (1) identify factors controlling permeability loss during oil injection; (2) demonstrate the efficacy of the process in continuous flow column experiments and identify critical failure modes that may limit performance in the field; (3) identify factors controlling the rate of oil solubilization and/or biodegradation in representative aquifer sediments; (4) modify the numerical model RT3D to simulate emulsion transport and retention; (5) validate the model in three-dimensional radial flow sand tank experiments; and (6) evaluate the performance of the emulsion transport model for simulating the distribution of oil and the impact of oil injection on chlorinated solvent biotransformation at a representative field site.
In this process, low-solubility edible oils are distributed in the subsurface to enhance anaerobic biodegradation of contaminants. An oil-in-water emulsion is first prepared using food-grade edible oils and surfactants. The emulsion is then injected into the contaminated aquifer using either conventional wells or Geoprobe points. As the emulsion passes through the aquifer, a portion of the oil becomes trapped within the pores leaving a residual oil phase. Over time, the residual oil slowly ferments to hydrogen and acetate, which are used by indigenous or bioaugmented microorganisms to degrade the target contaminants.
Edible oil barriers have significant cost and operational advantages. Emulsified oils are easy to inject and distribute using temporary or permanent wells and can be distributed 20 to 50 feet from injection points. Total installation costs are often substantially lower than for competing technologies. (Project Completed - 2008)