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USGS Patents Bioreactors that Treat Nitrate and Methyl Bromide Contamination

U.S. Geological Survey (USGS) scientists have developed and patented two bioreactor treatment systems. One is designed to remove dissolved nitrate from water supplies. The second is designed to remove gaseous methyl bromide from the exhaust that results from the fumigation of shipping containers. The systems are called bioreactors because they make use of specialized bacteria for efficient and cost-effective removal of the contaminants.

Nitrate Bioreactor

Many households in the United States have ground water with elevated nitrate concentrations. High nitrate concentrations in drinking water are associated with adverse health effects, such as blue-baby syndrome. To help solve this problem, USGS scientist Richard L. Smith has designed, constructed, and patented (patent number 6,863,815 B1) a bioreactor that utilizes specialized microorganisms (hydrogen-oxidizing, denitrifying (HOD) bacteria) to remove excess nitrate from water supplies. The bacteria used in the reactor were originally isolated from sediments at the Toxic Substances Hydrology Program's research site on Cape Cod. The nitrate bioreactor is designed as a small-scale unit to treat single-well water supplies, which are typically affected by rural, non-point sources of nitrate contamination. The HOD bacteria in the bioreactor use hydrogen and nitrate to grow, and produce only water and nitrogen gas in the process, both of which are harmless end-products. The unit generates the hydrogen for the bacteria by the electrolysis of water. As a safety feature, the bioreactor is designed to contain only small amounts of hydrogen at any one time, and it produces the hydrogen only when needed. The inventor tested the bioreactor with ground water and surface water being used for home water supplies. He found the bioreactor to be functional and stable for long periods of time and capable of completely removing high levels of nitrate with only a 2-hour contact time.

Laboratory-scale bioreactor for removing nitrate from water.
Laboratory-scale bioreactor for removing nitrate from water. Shown here is the bioreactor after 250 days of continuous bacterial growth. The purple pigmentation in the nitrate-free zone is created by the bacteria.

References

  • Smith, R.L., Buckwalter, S.P., Repert, D.A., and Miller, D.N., 2005, Small-scale, hydrogen-oxidizing-denitrifying bioreactor for treatment of nitrate-contaminated drinking water: Water Research, v, 39, p. 2014-2023.
  • Smith, R.L., 2005, Small-scale hydrogen-oxidizing-denitrifying bioreactor: Washington, D.C., U.S. Government Patent and Trademark Office, United States Patent No. 6,863,815 B1.

More Information

More Information on Nitrate

Methyl Bromide Bioreactor

Seaports all along the coasts receive thousands of shipping containers each day that are routinely fumigated with methyl bromide to prevent non-native insects and other unwanted organisms from invading the country. The downside of this practice is that the methyl bromide (also know as bromomethane) exhausted to the atmosphere from fumigation operations has a negative impact on the Earth's ozone layer. In addition, methyl bromide is hazardous to human health. USGS scientists Larry Miller, Ron Oremland, and Shaun Baesman have received a patent (patent number 6,916,446) for a bioreactor that removes methyl bromide from the exhaust from fumigation operations. The bioreactor contains a culture of specialized microorganisms (methylotrophic bacteria) that removes methyl bromide from the exhaust by oxidizing it to carbon dioxide, hydrobromic acid, and water. A 1,000-liter bioreactor is capable of removing 10 kilograms (kg) of methyl bromide in 50 hours. The development of the bioreactor is a practical application of the extensive research by these scientists on microorganisms in the natural environment that degrade methyl bromide and other methyl halides (see text box).

Laboratory-scale bioreactor for removing methyl bromide.
Laboratory-scale (10 liter) bioreactor for removing methyl bromide from the exhaust from fumigation operations. The fermenter contains 3 x 1012 cells of methylotrophic bacteria, Aminobacter ciceronei, capable of oxidizing 0.12 g of methyl bromide per hour.

References

  • Miller, L.G., Oremland, R.S., and Baesman, S.M., 2005, A bioreactor for the oxidation of the fumigant methyl bromide: Washington, D.C., U.S. Government Patent and Trademark Office, United States Patent No. 6,916,446.
  • Miller, L.G., Baesman, S.E., and Oremland, R.S., 2003, Bioreactors for removing methyl bromide following constrained fumigations: Environmental Science and Technology, v. 37, no. 8, p. 1698–1704.
  • Oremland, R.S, Connell, T.L., and Miller, L.G., 2000, Method for enhancing oxidation of methyl bromide with strain IMB-1: Washington , D.C., U.S. Government Patent and Trademark Office, United States Patent No. 6,013,254.

More Information

More Information on Methyl Bromide (Bromomethane)

Bacterial Oxidation of Methyl Bromide References

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Created on December 20, 2005