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(P800) QUANTIFYING BACTERIA IN A KARST AQUIFER FOR BIOREMEDIATION MODEL.
AGYEMANG, DANIEL*,1, BYL, THOMAS1,2, 1 CIVIL & ENVIRONMENTAL ENGINEERING DEPARTMENT, NASHVILLE, TN, U.S.A2 US GOELOGICAL SURVEY,640 GRASSMERE PAK, ,SUITE, NASHVILLE, TN, U.S.A
ABSTRACT- It has been assumed that there are fewer bacteria in karst aquifers compared to unconsolidated aquifers because there is less surface area for biofilm development,hence the belief that no significant biodegradation of contaminants takes place in karst conduits due to low bacteria counts.However, recent research indicates that biodegradation of fuel contaminants can occur in a karst aquifer (Byl and others, 2001). This implies that karst bacteria numbers may be higher than assumed because they have developed free-living morphologies suitable for conduit conditions. Microcosms were established using water and bacteria from the karst aquifer to measure the rate of benzene biodegradation. The rate of biodegradation ranged from 50% removed (T1/2) in 1 to 14 days. This broad range of biodegradation rates appears to be the result of initial bacteria concentration since all other conditions were similar. Thus, any mathematical equation that is used to describe the rate of fuel biodegradation in karst should incorporate bacteria concentration The objective of this research was to find the best technique to measure karst bacteria for such an equation. This objective was achieved by using several techniques to measure bacteria concentrations in water from clean and fuel-contaminated karst-aquifer wells. The techniques included heterotrophic plate counts (a traditional bacteria counting method), direct bacteria counts using a microscope and dyes, optical density at 687nm in a spectrophotometer, fluorescence of fluorescent bacteria using a fluorometer, and Biological Activity Reaction Test (BART). The methods are evaluated for accuracy, repeatability, expense and ease of use. The direct count and BART tests gave high counts ranging from 100,000 bacteria per milliliter to 1.3 million bacteria per milliliter. The heterotrophic plate counts consistently gave results that were 3 or more orders of magnitude lower than the direct count or BART tests. The optical density and fluorometer methods both require that another method be used to set up a calibration curve. The fluorometer appears to be more sensitive and have a straighter calibration curve than a spectrophotometer reading. Also, the fluorometer tends to measure fluorescing bacteria such as Pseudomonas fluorences which are known to biodegrade fuels.
Key words: BART
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