BIODEGRADATION OF THE PESTICIDE 4,6-DINITRO-ORTHO-CRESOL BY MICROORGANISMS IN BATCH CULTURES AND IN FIXED-BED COLUMN REACTORS

A mixed culture of microorganisms able to utilize 4,6-dinitro-ortho-cr esol (DNOC) as the sole source of carbon, nitrogen and energy was isol ated from soil contaminated with pesticides and from activated sludge. DNOC was decomposed aerobically in batch cultures as well as in fixed -bed column reactors. Between 65% and 84% of the substrate nitrogen wa s released as nitrate into the medium, and 61% of the carbon from unif ormly C-14-labelled DNOC was recovered as (CO2)-C-14. The mixed microb ial culture also decomposed 4-nitrophenol and 2,4-dinitrophenol but no t 2,3-dinitrophenol, 2,6-dinitrophenol, 2,4-dinitrotoluene, 2,4-dinitr obenzoic acid or 2-sec-butyl-4,6-dinitrophenol (Dinoseb). Maximal degr adation rates for DNOC by the bacterial biofilm immobilized on glass b eads in fixed-bed column reactors were 30 mmol day(-1) (1 reactor volu me)(-1), leaving an effluent concentration of less than 5 mu g l(-1) D NOC in the outflowing medium. The apparent K-s value of the immobilize d mixed culture for DNOC was 17 mu M. Degradation was inhibited at DNO C concentrations above 30 mu M and it ceased at 340 mu M, possibly bec ause of the uncoupling action of the nitroaromatic compound on the cel lular energy-transducing mechanism.