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(191) Enhanced biodegradation of chlorinated solvents in a karst aquifer using lactic acids .
Byl, Tom*,1,2, Hampton, LyTreece2, Chakaraborti, Koushik2, Ary, Alham2, Hileman, Gregg1, 1 USGS, Nashville, TN, USA2 College of Engineering, Tennessee State University, Nashville, TN, USA
ABSTRACT- A sanitary landfill situated on a karst terrane in northern Tennessee is leaking chlorinated solvents, primarily trichloroethylene (TCE) and its breakdown products. These compounds have been found in water from the karst bedrock aquifer, implying that they are in the conduits. It appears that some biodegradation has occurred by the appearance of breakdown products. Also, indigenous sulfur-reducing bacteria have been measured in water collected from wells screened in the karst bedrock. Additional water from the karst bedrock was collected and used to make 250 mL water microcosms. These microcosms were stocked with 5 ppb perchloroethylene (PCE) and different formulations of lactic acid, including 50 mg/L crude lactic acid (30%), sodium lactate (60%) and methyl-lactate. Preliminary results indicate that these lactic acids stimulated the reductive dechlorination of PCE to TCE and cis-dichloroethylene (cDCE). Within 2 weeks, there was a 25-30% decrease in PCE from the initial concentration and a subsequent rise in TCE. Within 4 weeks, there was a 40-60% decrease in PCE from the initial concentration. There was also a significant decrease in TCE and rise in cDCE compared to week 2. The microcosms treated with methyl-lactate also appeared to stimulate cometabolism for a short period, as evident by the disappearance of all cDCE and dissolved oxygen. These preliminary results indicate that lactic acids can stimulate reductive dechlorination of chlorinated solvents in water microcosms. Further tests are needed establish if these results extend to the field.
Key words: karst aquifer, biodegradation, chlorinated solvent, microorganism
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