Aerobic biological treatment of 2,4-dinitrotoluene in munitions plant wastewater

Wastewater from the manufacture of propellants typically contains 2,4-dinit rotoluene (DNT), a known animal carcinogen. Previous studies have indicated that DNT is aerobically biodegradable. However, inconsistent removal of DN T during aerobic treatment has been observed at a munitions wastewater trea tment plant, necessitating the use of activated carbon pretreatment. The ob jective of this study was to evaluate the effect of nutrient and cosubstrat e amendments on the rate and extent of DNT removal. Addition of ethanol (10 0-500 mg/l) and phosphate (0.8-3.3 mg/l) significantly accelerated the rate of aerobic DNT (0.3-5.6 mg/l) biodegradation. Addition of phosphate alone also increased the rate of DNT degradation, bur to a lesser degree. The pre sence of ethyl ether, another substrate commonly found in munitions plant w astewater. had comparatively little affect on the, rate of DNT removal. Int erruptions in the DNT manufacturing process can result in DNT being absent from the munitions plant wastewater for extended periods. The effect of suc h interruptions was evaluated in semicontinuously operated reactors, fed da ily with phosphate-amended wastewater (containing no detectable background level of DNT), at a hydraulic residence time of 3 d. DNT was added at varyi ng intervals (from once every 3 d to once every 15 d), DNT removal resumed without a lag even after it was absent from the feed for periods up to 15 d ; During aerobic biodegradation of DNT, reduction to 4-amino-2-nitrotoluene and 2-amino-4-nitrotoluene was consistently observed, with reduction at th e para position predominating. The highest level of aminonitrotoluene forma tion was 23% of the total DNT degraded. Aminonitrotoluene isomers were cons umed within 1 d after the DNT disappeared in the semicontinuously operated reactors. confirming the potential for degradation of these metabolites. Al though the aminonitrotoluene isomers are not currently regulated, their pre sence in treated munitions wastewater is a concern due to possible toxicity . (C) 2000 Elsevier Science Ltd. All rights reserved.