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Bioremediation of Perchlorate in Ground WaterRiverside, CASource: Research Summary W-902 in Research Program Activities of Water Resources Center, University of California 1998-1999, available at http://waterresources.ucr.edu/publications/AR9899-copy%20(1).pdf. Project Summary: The following text was excerpted from Research Summary W-902 in Research Program Activities of Water Resources Center, University of California 1998-1999, available at http://waterresources.ucr.edu/publications/AR9899-copy%20(1).pdf: Bioremediation is a viable option for perchlorate removal from ground water, as some bacteria can transform perchlorate into an innocuous end product, chloride. The bacterium, percIace, was isolated from a biosolids enrichment. This bacterium can use perchlorate as an alternate electron acceptor, instead of oxygen, for growth. In batch culture, this isolate completely transformed perchlorate into chloride in 48 hours with simultaneous removal of nitrate. PercIace will reduce perchlorate when acetate is the carbon source. Optimum growth conditions include a pH between 7.0 and 7.2 and a temperature of 30 deg.C. Anaerobic conditions are important, as the bacterium will also use oxygen as an electron acceptor and will not begin to reduce perchlorate until all of the oxygen is removed from the medium. PerIcace was not identifiable by standard methods, indicating that it may be a novel organism. PercIace was tested in a flow-through system to stimulate a potential bioreactor design. Using a 30-ml glass column, perIace was immobilized on a sand matrix. At various flow rates through the column, the bacterium was able to completely remove perchlorate and nitrate from mineral salts medium. A 300-ml column made of PVC pipe was designed with diatomaceous earth pellets (Celite) as the solid support for the bacterium. This column was used to demonstrate the removal of 738 g L-1 perchlorate from San Gabriel Valley ground water to levels below the State Action Level. A residence time in the column of 5 hours resulted in removal of perchlorate to less than 4 ppb, the current detection limit. At a residence time of 2.5 hours, perIace removed perchlorate from the ground water to below the State Action Level. These studies demonstrated the potential for perIace to be used as a means for removing perchlorate from ground water in a flow-through bioreactor system. It appears that the extent of perchlorate removal is flow rate dependent. A contributing factor may also be the distribution of biomass throughout the reactor. Another, larger column study is currently underway. This study intends to minimize the residence time of ground water in the column by increasing the biomass attached to the solid support. A faster flow of water through the column will make the system more economically feasible. Another aspect of the project involves investigation of alternative carbon sources for perchlorate bioremediation. A stable consortium of bacteria, which can grow with hydrogen as the electron donor, perchlorate as the electron acceptor and bicarbonate as the carbon source, has been cultured. Investigation of the growth kinetics of this consortium demonstrated that it can use bicarbonate and perchlorate already present in ground water as a growth substrate. This consortium may be a valuable bioremediation tool, as the consortium would not require the addition of a carbon source for growth. Water utilities need treatment methods that can reliably reduce perchlorate concentrations to low or nondetectable levels. The treatment method must be cost-effective, acceptable to regulatory agencies and the public, cause not other water quality problems and minimize waste generation. Because the perchlorate ion is nonvolatile and highly soluble in water, it cannot be removed by conventional methods. The most commonly used method for reducing perchlorate levels in contaminated water supplies is to blend the water with an uncontaminated supply. Some cities, including Loma Linda and Redlands, must purchase expensive water to meet the demands of these communities. The use of microorganisms immobilized in a flow-through bioreactor for the removal of nitrate is a common strategy used in Europe and one such system is in place in the United States. Development of this type of system for perchlorate removal would be a great advance in technology, as current remediation methods such as ion exchange and reverse osmosis, are capable only of concentrating perchlorate, not destroying it. Bacterial metabolism of this contaminant would be an efficient, cost-effective process for completely removing perchlorate from the environment. Additional Info Source: Giblin, T., D.C. Herman, and W.T. Frankenberger, Jr. 1999. Bacterial reduction of perchlorate and nitrate in groundwater by perIace. Presented at the Perchlorate Conference, Ontario, California. Giblin, T., D.C. Herman, and W.T. Frankenberger, Jr. 1999. An autotrophic system for removal of perchlorate from groundwater. Presented at the Perchlorate Symposium, Annual Meeting of the American Chemical Society. New Orleans, August. Herman, D.C. and W.T. Frankenberger, Jr. 1999. Bacterial reduction of perchlorate and nitrate in groundwater, in Journal of Environmental Quality 28:1018-1024. Herman, D.C. and W.T. Frankenberger, Jr. 1998. Microbial-mediated reduction of perchlorate in groundwater, in Journal of Environmental Quality 27:750-754. Research Summary W-902 in Research Program Activities of Water Resources Center, University of California 1998-1999, available at http://waterresources.ucr.edu/publications/AR9899-copy%20(1).pdf. |
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