Bacterial growth on N,N-dimethylformamide:: implications for the biotreatment of industrial wastewater

The degradation of N,N-dimethylformamide (DMF) by bacterial consortia was investigated under aerobic, fermentative and nitrate-reducing conditions and a variety of salt concentrations (0.2%, 4% and 7% NaCl w/v) and pH values (5 and 7), Optimization of degradation conditions was studied to provide information and recommendations for large-scale biological treatment processes. Under aerobic conditions, mineralization of DMF (200 mg l(-1), 2.7 mM) was achieved under all combinations of salinity and pH. The rate of bacterial growth decreased with increasing salinity. Changes in the salt concentration and pH still resulted in mineralization and unchanged yield of bacterial cells. At 0.2% NaCl and either pH 5 or 7, growth occurred on DMF in the range 0.2-1 g l(-1), However, cell yield decreased with increasing concentrations of DMF. Under conditions of 0.2% NaCl, pH 7 and 4% NaCl, pH 5, growth on DMF at 5 g l(-1) resulted in the production of an intermediate that was detected using gas chromatography (GC). It is proposed that the intermediate was dimethylamine, and its persistence in growth media;was attributed to suppressed growth as a result of an increase in pH. A culture capable of degrading DMF under nitrate-reducing conditions was obtained at 0.2% NaCl and pH 7, but not at more saline and acidic conditions. Growth and degradation of DMF were considerably slower under these conditions compared with aerobic conditions. Fermentative degradation of DMF was not observed.