Groundwater Study Program Initiates Pilot Test For Possible Perchlorate Treatment
Camp Edwards, Mass. — A pilot test of a treatment technology for perchlorate contamination in groundwater is now underway at Camp Edwards. The Impact Area Groundwater Study Program is exploring the use of fluidized bed reactors to treat contaminants found in groundwater on the upper 15,000 acres of the Massachusetts Military Reservation.
Fluidized bed reactors, which use naturally occurring microorganisms to break down groundwater contaminants, are currently being used in Texas and California to successfully treat perchlorate-contaminated groundwater. The Groundwater Study Program’s pilot test, being conducted by Envirogen, Inc., is designed to see if this same technology can be used to simultaneously eliminate perchlorate, a component of military propellants and munitions, and RDX, an explosive, which were both formerly used at Camp Edwards.
According to Groundwater Study Program Manager Ben Gregson, most perchlorate detections at Camp Edwards are in areas where RDX has been found. "This presents a unique challenge. The usual RDX clean up method of granular activated carbon alone, hasn’t been shown to work efficiently for perchlorate. We are looking at the fluidized bed reactor as a single solution for both of these contaminants."
The fluidized bed reactor removes the contaminants by pumping water upwards through a bed of granular activated carbon, inhabited by contaminant-cleaning microorganisms. The microorganisms are injected into the system where they attach to the carbon and grow to form a "biofilm". Then, in much the same way as humans take in oxygen and exhale carbon dioxide, the biofilm takes in the perchlorate for respiration as the groundwater passes through the reactor. It is reduced to water and chloride, a component of table salt, and expelled.
The pilot test, being conducted at Camp Edwards, is using three small models of the fluidized bed reactor. "These scaled-down units are being operated so that the perchlorate and RDX treatment results will be the same as we would expect to see for full-sized systems," Gregson explained.
Two of the fluidized bed reactors will gauge the system’s ability to remove contaminants using different food bases (substrates) -- vinegar and molasses -- for the microorganisms. A third system will serve as a control, running the contaminated water through a cylinder of granular activated carbon without a biofilm.
Part of the pilot test is to determine if one of the substrates will be more effective in promoting the breakdown of both contaminants. In Texas, an acetic acid (vinegar) food base is being used to clean perchlorate concentrations of up to 40,000 parts per billion to less than 4 parts per billion. In the Groundwater Study Program’s test, molasses was selected as the second test base because it contains compounds shown to be effective in promoting the breakdown of RDX.
The trial at Camp Edwards will be using groundwater from a monitoring well in Demolition Area 1, which contains RDX concentrations of 200 parts per billions and perchlorate concentrations of 100 parts per billion.
According to Gregson, the fluidized bed reactor has been successful at cleaning perchlorate concentrations that are hundreds of times higher than those being found at Camp Edwards. However, in addition to the presence of RDX in the groundwater, this test presents the additional challenge of meeting the 0.35 parts per billion detection limit for perchlorate used by the Groundwater Study Program.
"In Texas and California they are only looking at a cleanup limit of 4 parts per billion for perchlorate and the treatment technologies currently in use haven’t really
been tested at the lower limits being used at Camp Edwards," Gregson explained. "Envirogen’s system has been tested at 0.87 parts per billion, so we hope to prove through the pilot test that these fluidized bed reactors can remove perchlorate to our lower detection limit."
The pilot test, which will run through June, will begin with an evaluation of whether the fluidized bed reactor can simultaneously break down the perchlorate and RDX in the groundwater. When that is known, the next phase will be to test the variables, such as the required food base level and water flow rate, to find the operating capacity of a full-sized fluidized bed reactor system. This will help determine the size of the system that would be needed at Camp Edwards.
A full-sized system can be designed, constructed and operating within four to five months. A single fluidized bed reactor unit can clean almost two million gallons of water a day. One such system has been successfully treating perchlorate-tainted water in California for more than 2 years.
According to Gregson, the fluidized bed reactor has low maintenance costs and is environmentally friendly. In addition, everything about the fluidized bed reactor’s treatment is organic, with the only waste produced being non-hazardous, biodegradable solids.
"The biofilm consists of microorganisms that are naturally occurring in local soil, although the ones being used in the test were supplied by the contractor. The food bases are natural and the carbon only requires cleaning, not replacement," Gregson explained.
The biofilm in the fluidized bed reactor destroys contaminants in groundwater, rather than capturing and concentrating them for subsequent disposal. A sand filter is installed on the system to catch any stray particles of carbon or biofilm, so that nothing is introduced into the ground that wasn’t there before. It just puts back cleaned water.
Due to their ability to treat water without the introduction of non-food-grade chemicals, fluidized bed reactors have just received approval to be used for drinking water production in California. Mr. Gregson said that since the fluidized bed reactor is not yet approved for wellhead treatment in Massachusetts, the Groundwater Study Program is not currently considering it for that, but believes that the California approval confirms the benefits of the system’s biological approach to contaminant removal.
Based on the pilot test results, Mr. Gregson would like to consider the system for use in cleaning up RDX and perchlorate contaminated groundwater at Camp Edwards.
"We are looking forward to moving ahead with cleanup in the areas of contamination we’ve identified in the Central Impact Area and Demolition Area 1," Gregson said. "We are testing the fluidized bed reactor and other options now, so that we can rapidly move to the clean up phase of our project when we finalize the delineation of the plumes."
The Impact Area Groundwater Study Program, led by the National Guard Bureau, has been working on an investigation and cleanup of the upper 15,000 acres at Camp Edwards since 1997. The Environmental Protection Agency and the Massachusetts Department of Environmental Protection oversee the program.
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