CEE student builds device to treat perchlorate in water
An engineering student has built a device that could prove to be a better way to remove perchlorate contamination from water. Robert McKeever, a senior in the Civil and Environmental Engineering (CEE) Department, has designed and built a pilot bioreactor that uses common soil bacteria to “eat” perchlorate, an anion used in rocket fuel, fireworks, defense manufacturing and other industries. McKeever’s pilot bioreactor is being tested at the Massachusetts Military Reservation (MMR) in Bourne, which has been using the current state-of-the-art technique for removing perchlorate from drinking water, a method known as “ion exchange.”
McKeever is working on a research project led by Sarina Ergas, associate professor in CEE, and funded for $300,000 by the National Science Foundation. Along with graduate students in Environmental Engineering and Microbiology, McKeever recently installed the pilot bioreactor at a well on the MMR property and is now collecting data to measure its effectiveness eliminating perchlorate. The technique has already been successfully tested in the lab on a smaller scale. If the pilot bioreactor confirms those laboratory test results, the new method would be substantially less expensive than the ion exchange technology, and it would create none of the waste products.
“My job was designing and constructing the bioreactor to remove perchlorate from the ground water in the MMR,” says McKeever. “So basically you pump up the water through the bioreactor. And the whole system has those bacteria in it. They are eating the perchlorate.”
At least 36 states have water with perchlorate contamination. High levels of perchlorate are associated with thyroid disease and other health problems. McKeever’s bioreactor is designed to be used by public utilities that are treating drinking water contaminated with perchlorate.
The MMR is a 22,000-acre property that has been used for military training activities since 1911 and is located over a sole source aquifer that provides drinking water for the town of Bourne. The MMR property includes Otis Air National Guard Base, Camp Edwards and the Coast Guard Air Station Cape Cod, and has been declared a Superfund Site by the U.S. Environmental Protection Agency.
McKeever’s bioreactor is constructed from a polyurethane tank three feet tall and two feet in diameter. A pump brings up ground water from the aquifer 180 feet below and circulates it through the tank. A five-inch layer of gravel on the bottom of the tank helps distribute the flow of water. The rest of the tank is filled with 200 liters of oyster shells and sulfur pellets. The oyster shells provide the proper alkalinity for the process, while the sulfur pellets act as nutrients for a special strain of perchlorate-reducing autotrophic bacteria, developed in the Environmental Engineering and Microbiology departments. Sulfur is a waste product of oil refining and oyster shells are available from oyster processors, so the material is cheap and readily available. The biological reaction produces chloride, sulfate and oxygen, which are harmless products.
The NSF-funded research project is entitled, “A Novel Method for Biological Perchlorate Reduction Using Elemental Sulfur as an Electron Donor.” As the NSF proposal explains, “This project describes a novel process to entirely break down perchlorate in contaminated ground and surface waters to innocuous products.” The co-principal investigator is Klaus Rudolf Nüsslein of the Microbiology Department. Nüsslein is investigating the perchlorate-reducing bacterial community.
If it proves effective, the new technology would be a significant upgrade over ion exchange. First of all, the new technique is much less expensive than ion exchange, which requires the purchase of expensive resins. Also, in ion exchange, perchlorate is transferred from the water to a resin material in a packed bed. Once the packed bed is full of perchlorate, it must either be disposed of off-site or be regenerated using a brine solution, creating a brine waste that is high in perchlorate.
McKeever’s pilot-scale bioreactor experiments at the MMR site will be used to examine the operational stability of the new technique, the scale-up to larger bioreactors and potential costs for typical water utility applications.
His data will also measure this method’s effects on the other contaminants at the MMR. Two other contaminants connected with the MMR site are RDX and HMX, two explosive nitroamines widely used in military and industrial applications. It’s quite possible that the new bioreactor will help remove these two nitroamines from the water, but that possibility hasn’t been proven yet, and removing those two contaminants would be an additional benefit of the research project.
December 3, 2008.
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