CASE HISTORY FOR TREATING CONTAMINATED GROUNDWATER WITH COMETABOLIC METHANOTROPHIC BIOREMEDIATION

摘要

Site investigations at a manufacturing facility in Virginia identified three soil and groundwater contaminant source areas. Each source area had a different volatile organic compound (VOC) profile of chlorinated solvents trichloroethylene (TCE); 1,1,1- trichloroethane (TCA); and associated breakdown products (cis-1, 2-dichloroethene (DCE), vinyl chloride (VC), 1,1-dichloroethane (DCA), and chloroethane (CA)); as well as acetone and isopropanol in soil and groundwater in a fractured rock aquifer. Chemical and microbiological sampling over time confirmed that natural biodegradation of these compounds was occurring at a limited rate. In-situ aerobic cometabolic bioremediation was implemented at three on-site source areas to stimulate existing microbial populations to accelerate the degradation of target VOCs. Results of pilot and full-scale bioremediation efforts have been successful to varying degrees at each of these different locations. The first source area at this site where the bioremediation technology was applied contained the chlorinated hydrocarbons, acetone and isopropanol. Monitoring data indicate that the enhanced bioremediation program has been successful in stimulating microbial growth based on increases in phospholipid fatty acid (PLFA) biomass and methanotroph most probable number (MPN) measurements of several orders of magnitude within four months of system start-up throughout full-scale operation. Initial total VOC concentrations ranged from 10,000 ug/l to >1,000,000 ug/l. Groundwater monitoring indicates significant (99 to 99.96%) total VOC reductions in this source area, and in some downgradient monitoring locations. However, after this significant VOC reduction, VOC concentrations in groundwater from some of the monitoring wells remain above drinking water standards despite approximately four years of system operation. The second source area contained primarily acetone and isopropanol in groundwater. The acetone and isopropanol concentrations in this source area ranged from 200,000 ug/l to 500,000 ug/l for each compound prior to initiation of the bioremediation system. Following three months of system operation, the acetone and isopropanol concentrations were below detection limits in several wells.