(In Situ Bioremediation by Electrokinetic Injection)
In situ bioremediation is the process of introducing process nutrients into biologically active zones (BAZ). These nutrients are usually introduced by pumping recirculated groundwater through the BAZ, relying on hydraulic gradients or the permeability of the BAZ. However, heterogeneities in aquifers often hinder the introduction of the nutrients. For example, areas with higher permeability result in preferential flow paths, leading to incomplete biological treatment. The inability to uniformly introduce nutrients and other additives, such as surfactants and cometabolites, has hindered the successful implementation of in situ bioremediation.
Electrokinetics, Inc. (Electrokinetics), is developing an electrokinetic remediation technology that stimulates and sustains in situ bioremediation for treatment of organics and heavy metals. The technology involves applying to soil or groundwater a low-level direct current (DC) electrical potential difference or an electrical current using electrodes placed in an open or closed flow arrangement. Groundwater or an externally supplied processing fluid is used as the conductive medium. The low-level DC causes physicochemical and hydrological changes in both the waste and the conductive medium, thereby enabling uniform transport of process additives and nutrients into the BAZ, as shown in the figure below.
The Electrokinetics technology is designed to overcome the problems associated with aquifer heterogeneities, unlike conventional in situ injection by hydraulic techniques. The rate of nutrient and additive transport under electrical gradients is at least one order of magnitude greater than that achieved under chemical gradients.
Electrokinetic injection can be used for any waste that can be treated by bioremediation. The technique allows in situ treatment of contaminated subsurface deposits, sediments, and sludges. The technology can be engineered to remove inorganics through electromigration and electroosmosis, while process additives and nutrients are added to the processing fluids to enhance bioremediation of organics.
This technology was accepted into the SITE Emerging Technology Program in 1995. Pilot- scale studies under the Emerging Technology Program will be used to develop operating parameters and to demonstrate the efficiency and cost-effectiveness of the technology during a full-scale application. The SITE evaluation may take place in 1997 at a military base or a U.S. Department of Energy site.
Electrokinetics is studying enhancement techniques to remove, or prevent the formation of, precipitates near the cathode during removal of inorganics. A 1993 study suggested that adding acetic acid may depolarize the cathode reaction, preventing precipitate formation. This study was conducted by Electrokinetics and Argonne National Laboratory under a U.S. Department of Defense Small Business Innovative Research grant. The study assessed nutrient movement through clean soils of different hydraulic conductivities; samples for the study were taken from Idaho National Engineering Laboratory and the Savannah River Site. Currently, bench- and pilot-scale tests are being conducted on soils containing trichloroethene and hydrocarbons of interest.
Electrokinetics has remediated several sites in conjunction with its proprietary electrode system (CADEX™ electrodes). Under a Small Business Innovative Research grant from the U.S. Waterways Experiment Station, Electrokinetics has tested its technology on soils from Fort Polk in Louisiana, and the Naval Depot in Hastings, Nebraska. Current activities include movement of biological additives through mixed soil horizons and directing these additives to sources of organic compounds for electrokinetically enhanced degradation.
EPA PROJECT MANAGER:
Randy Parker
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7271
Fax: 513-569-7571
TECHNOLOGY DEVELOPER CONTACT:
Elif Acar
Electrokinetics, Inc.
11552 Cedar Park Avenue
Baton Rouge, LA 70809
504-753-8004
Fax: 504-753-0028
E-mail: ekinc@pipeline.com