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NSWC Indian Head Performs First East Coast Bioremediation of Perchlorate

NAVSEA News

By Dr. Randall J. Cramer, NSWC Indian Head Division Applied Technology Department

INDIAN HEAD, Md. -- Innovative science and technology measures recently reaffirmed the Naval Surface Warfare Center Indian Head Division's commitment to the protection of public health and the environment in helping to solve what has become a national problem. Indian Head Division's Applied Technology Department together with Envirogen, Inc. successfully demonstrated the use of naturally occurring microorganisms to clean up groundwater contaminated with perchlorate, an ingredient used in military munitions such as pyrotechnics, explosives, mines, and rocket fuels.

Ammonium perchlorate has been used since the 1940s in the United States as an oxidizer in solid propellants and explosives. At present, there is no national environmental standard regulating perchlorate.

Based on risk assessment studies, which indicated that large doses of perchlorate may have an adverse impact on human thyroid functions, it is anticipated that the Environmental Protection Agency (EPA) will propose new regulatory standards for perchlorate at levels as low as one to 14 parts per billion.

Remediation to these levels would be extraordinarily expensive unless innovative and practical cleanup methods, such as the one demonstrated at Indian Head, are developed.

The study area at Indian Head Division was used to clean out solid propellant containing ammonium perchlorate from various devices, including rockets and ejection seat motors, that have exceeded their useful life span. Past waste-handling methods have impacted the groundwater at this site where the wash water is now recycled.

Using a re-circulation cell design, naturally occurring microorganisms were stimulated to degrade perchlorate by injecting a food source (lactate) and neutralizing the groundwater acidity with a carbonate buffer. Starting with perchlorate concentrations in excess of 210 milligrams per liter, perchlorate levels were reduced by more than 95 percent in eight to nine monitoring wells within five months of testing.

In two of the monitoring wells, the perchlorate levels were lowered to less than five parts per billion. In addition to the perchlorate levels and the pH, alkalinity, nitrate, and sulfate concentrations were measured.

Since perchlorate is unreactive and very soluble in water, the development of suitable groundwater remediation and treatment technologies is difficult. However, specific types of bacteria have been found to metabolize perchlorate during growth when fed appropriate substrates, such as lactate, acetate, molasses and ethanol. Subsequently, perchlorate is converted completely to a chloride ion and oxygen, which is safe for the environment.

Naturally occurring perchlorate-degrading bacteria were found to be present, and pure cultures of the genera Dechlorosoma and Dechlorospirillum were isolated. Bioremediation treatment technology is based on getting these microbes to grow by providing a food source and adjusting the pH of their environment, then allowing them to metabolize the perchlorate present in the water.

These in-situ bioremediation techniques are much less expensive and significantly easier to maintain than traditional ex-situ pump-and-treat systems.

Indian Head Division is sharing it's findings with the Navy community, including Naval Facilities Engineering Command, in an effort to proactively find a solution to what has become a national concern.