Denmark draws DECON expertise from ERDC engineer

Published May 2, 2012
ERDC Engineer Dr. David Gent checks the electric current applied to one of the electrodes in an electrode well during his two-month demonstration project in Denmark.

ERDC Engineer Dr. David Gent checks the electric current applied to one of the electrodes in an electrode well during his two-month demonstration project in Denmark.

May 2, 2012

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SKULDELEV, Denmark — The Corps' present-day go-to engineer for electrokinetics (EK) recalls glancing at the photo of the Mississippi River model found in his McComb, Miss. history textbook in 1972 and thinking that WES would be a cool place to work.

Environmental Engineer Dr. David Gent said that memory resurfaced several years ago while working on one of the many highly regarded remediation process experiments he's conducted at ERDC since his initial employment in 1993.

Responding to a present-day request for his expertise and the opportunity to test his "ground-breaking" procedures, Gent traveled to Denmark in August 2011, where he assisted in the two-week installation and startup of a field-scale pilot demonstration of his EK-Bio in-situ remediation process.

Funded by The Capital Region of Denmark in the small village of Skuldelev, the project focuses on the clean up of a site contaminated with tetrachloroethene (PCE) as a result of past releases associated with a former industrial facility located nearby. The site receiving the beneficial cleaning is presently a residential area.

The results of the successful pilot demonstration will be presented in May at the Eighth International Conference on Remediation Compounds in Monterey, Calif.

Finally solving the problem

Gent said the PCE, an organic solvent commonly used as a dry cleaning fluid, is heavier than water and sinks in the ground, making it difficult to cleanup.

"EK-Bio is the fourth and last technology tested at the site for potential full-scale cleanup. The Capital Region, similar to our Environmental Protection Agency, plans to clean up the remaining contaminated area using the EK-Bio process," Gent said.

Field data shows vast improvements in diminishing contaminated soils surrounding the area, now home to local citizens and a popular park.

He explained PCE contamination ranged from 15 to as high as 1,200 mg/kg depending on the depth of contamination. Samples taken after the completion of the demonstration revealed that more than 90 percent of the PCE was removed from the soil at depths ranging from 11 to 30 feet below the ground surface. Groundwater samples at the end of the demonstration showed 87 to 100 percent of the contaminant removed.

Low energy use solution

The energy used in the field demonstration was about 1,900 kilowatt-hours, which is equivalent to nine 100-watt bulbs running for two weeks at a cost of approximately $200.

Gent explained his EK-Bio process as "an electrokinetics remediation technology for amending low permeability soils with electron donor and bioaugmentation with dehalococcoides microorganisms for biological degradation and mineralization of chlorinated solvents."

Continuing, he said the EK-Bio is shorted from electrokinetics-enhanced bioremediation. The process uses a low, power-direct current to deliver high concentrations of charged organic amendments such as lactate, a milk acid anion, into low permeability soils, clays and silt-like clays, as food for microorganisms to grow and increase their populations.

"The microorganisms actually do the work of removing the contaminant by breaking it down into smaller molecules that are non toxic. The reason electricity has to be used to deliver amendments is that the low permeability soils will not allow water to freely flow through them. In fact, it would take water at the Skudelev site one year to travel 12 inches through the soil containing the PCE contaminant, making it difficult to treat by conventional techniques. There are many different microorganisms that partially degrade the PCE contaminant, but the ones that complete the process are called dehalococcoides. If these organisms are not present, they may be added to the soil by the same process," said Gent.

The EK-Bio process also stimulates microorganisms to grow and reproduce under the applied electric field and increases the soil temperature further enhancing microbial growth and reproduction.

When funding sources were unavailable for larger-scale testing of his unique process in the U.S., Gent welcomed the chance to show what his technology could do in Denmark. Successfully testing and refining his system since 1995, Gent emphasized that "no was not an option" in proving the EK-Bio process capabilities.

While Gent provided electrokinetics treatment expertise, the demonstration is a joint collaboration with NIRAS, the operating contractor, and Geosystec Consultants, which provided the KB-1 dehalococcoides microorganisms, as well as extensive in-situ bioremediation knowledge.

Testing of the EK-Bio treatment system operated for two months in Denmark from mid-August though mid-November 2011, with monitoring continuing for six months.

Following the successful conference reports in May, the results will also be peer-review published, so other engineers and scientists can consider using the EK-Bio treatment systems successfully and closer to home.