The intermediates of microbial transformation of 2,4-dinitrotoluene by a mixed bacterial culture derived from activated sludge were identified as 2-amino-4-nitrotoluene, 4-amino-2-nitrotoluene, 2-nitroso-4nitrotoluene, and 4-nitroso-2-nitrotoluene. The biotransformation of 2,4-dinitrotoluene occurred only under anaerobic conditions with an exogenous carbon source. The two nitroso compounds were unstable and could be observed only at the early stage of 2,4-dinitrotoluene anaerobic biotransformation.
Efficient operation of the activated sludge process in a sewage treatment plant requires a simple, rapid, and accurate method for determining the biological activity in the mixed liquor. A test utilizing resazurin reduction by sludge microbial dehydrogenase has been adapted for the purpose. Biological activity by this method, 02-uptake rate, levels of mixed liquor suspended solids (MLSS), and heterotrophic bacterial count were determined on laboratory and pilot plant scale activated sludges. Good correlations, between resazurin reduction and all of these parameters, were observed. The rapid response of biological activity to nutrient loading and its sensitivity to toxicants in the activated sludge are reflected by the resazurin reduction method, which is a sensitive tool for routine plant monitoring work, as well as for research into sludge activity and process control.
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