Microbial removal of chlorinated hydrocarbon pesticides from water



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The removal of chlorinated hydrocarbon pesticides were examined by the use of two systems of microorganisms. One system was found to be composed of three Gram-negative bacteria. The second system was composed of four Gram negative bacteria, the three from the first system plus one additional organism. These organisms produced floc forming cultures which gave some evidence for the partial degradation of the pesticides by the identification of metabolic by-products and production of increased biomass. One of the organisms present in each system was shown to have small concentrations of bacteriochlorophyll and to function with CO2 as the only carbon source under anaerobic conditions. A complicated interrelationship of cross-feeding and synergistic growth was found to exist in the systems of mixed organisms. Light and electron microscopy studies showed initial pesticide removal was accomplished by adsorption to floc material formed by the systems, by absorption into the lipid material of the cells, and by a crystallization process carried out by certain cells. Flocculation was shown to be carried out by production of a polymer material of carbohydrate nature or by adsorption of individual cells to the highly charged pesticide material by means of surface charges. The environmental factors which regulated the flocculation process were examined and optimum conditions were determined. Both systems produced the best floc in shake cultures incubated at 30° C. The presence of light stimulated the amount and onset of floc formation in each system. Best flocculation was obtained when each system was grown in the presence of heptachlor and yeast extract. The optimum pH was 8.0 for System A and 7.0 for System D. System A showed best flocculation when 0.002% magnesium was present in the culture. Flocculation of System D cells was best with a magnesium concentration of 0.00002%.