Treatment of Perchlorate and 1,1,1-Trichloroethane in Groundwater using Edible Oil Substrate (EOS®)

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ABSTRACT: Laboratory studies and a pilot-scale field test are being conducted to evaluate the use of edible oil emulsions for biodegradation of perchlorate and 1,1,1-trichloroethane (1,1,1-TCA) in groundwater at a site in Maryland. The patented Edible Oil Substrate (EOS®) process is a cost-effective approach for stimulating in situ anaerobic biodegradation with little or no operation and maintenance. Laboratory microcosms showed rapid and complete removal of perchlorate with slower degradation of 1,1,1-TCA to measurable daughter products. Preliminary results from the pilot-scale permeable reactive biological barrier (PRBB) show complete removal of perchlorate in the injection and downgradient monitor wells as quickly as 5 days after injection. Within 68 days of EOS® injection, 1,1,1-TCA concentrations decreased by 95% in monitor wells located up to 20 feet downgradient of the PRBB. The barrier will continue to be monitored to evaluate the long-term effectiveness and cost associated with the use of EOS® for in situ biodegradation of perchlorate and 1,1,1-TCA.

INTRODUCTION
Groundwater and surface water contaminated with perchlorate (CIO 4') has become a major environmental issue for the U.S. Department of Defense (DoD) due to the use, release and/or disposal of solid rocket fuel and munitions containing ammonium perchlorate. Perchlorate is a highly mobile, soluble salt that sorbs poorly to most aquifer material and can persist for decades under aerobic conditions. However, recent research has shown that a very diverse array of bacteria can anaerobically degrade perchlorate to chloride and oxygen. These organisms appear to be widespread in the environment and can use a variety of different organic substrates as electron donors for perchlorate reduction.

Similarly, chlorinated solvents in groundwater are also a frequently encountered problem at DoD facilities. Anaerobic reductive dechlorination has been shown to be an efficient microbial means of transforming more highly chlorinated species to less chlorinated species. Chlorinated solvents amenable to in situ anaerobic bioremediation include tetrachloroethene (PCE), trichloroethene (TCE), c/s-l,2-dichloroethene (c/s-DCE), vinyl chloride (VC), 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,2-dichloroethane (1,2-DCA), carbon tetrachloride (CT), and chloroform (CF).

The patented EOS® process (U.S. Patent #6,398,960) provides an innovative, low-cost approach for distributing and immobilizing biodegradable organic substrates in contaminated aquifers to promote in situ anaerobic biodegradation of perchlorate and chlorinated solvents. EOS® consists of food-grade soybean oil, surfactants, macro and micro nutrients, and vitamins blended to form a stable micro-emulsion with small, uniformly-sized oil droplets. Once injected, the oil droplets stick to the sediment surfaces providing a residual oil phase. The EOS then serves as a carbon source for cell growth and an electron donor for energy generation, supporting long-term anaerobic biodegrade-tion of the target contaminants. This approach provides good contact between the slowly biodegradable organic substrate (oil) and the contaminants and substantially reduces initial capital and long-term operation and maintenance (O&M) costs.

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