Microbiological changes during bioremediation of explosives-contaminated soils in laboratory and pilot-scale bioslurry reactors

Changes in the microbial community during bioremediation of explosives-contaminated soil in a molasses-fed bioslurry process were examined. Upon addition of molasses to laboratory-scale reactors, total culturable heterotrophs increased rapidly by three to four orders of magnitude. However, heat-shocked heterotrophs and the percentage of gram-positive bacterial isolates did not increase until the soluble concentrations of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrobenzene (TNB) began to decrease. The number of identified phospholipid fatty acids (PLFA) and the total PLFA concentration also exhibited an immediate increase in response to molasses addition, while the concentration of branched PLFA, indicative of the gram-positive population, remained low until soluble TNT and TNB concentrations had significantly decreased. This same general relationship between explosives degradation and gram-positive-specific PLFA was observed during an experiment with a large field-scale bioslurry lagoon reactor. These results indicate that the gram-positive organisms, which have been shown to be severely impacted by even low concentrations of TNT and TNB [Current Microbiol. 35 (1997) 77; Environ. Toxicol. Chem. 17 (1998) 2185], are able to increase in concentrations after explosives compounds are reduced to non-inhibitory levels, and should therefore be able to reestablish themselves in remediated soils.