Bio-Kinetics of Simultaneous Nitrification and Aerobic Denitrification (SNaD) by a Cyanide- Degrading Bacterium Under Cyanide-Laden Conditions

A microorganism isolated and identified asAcinetobacter courvaliniiwas found to be able to perform sequential free cyanide (CN-) degradation, simultaneous nitrification and aerobic denitrification (SNaD); this ability was associated with the multiphase growth profile of the microorganism when provided with multiple nitrogenous sources. The effect of CN(-)on SNaD including enzyme expression, activity and protein functionality ofAcinetobacter courvaliniiwas investigated. It was found that CN(-)concentration of 1.9 to 5.8 mg CN-/L did not affect the growth ofAcinetobacter courvalinii. Furthermore, the degradation rates of CN(-)and ammonium-nitrogen (NH4-N) were found to be 2.2 mg CN-/L/h and 0.40 mg NH4-N/L/h, respectively. Moreover, five models' (Monod, Moser, Generic Rate law, Haldane, and Andrews) ability to predict SNaD under CN(-)conditions, indicated that, only the Rate law, Haldane and Andrew's models, were suited to predict both SNaD and CN(-)degradation. The effect of CN(-)on NH4-N, nitrate-nitrogen (NO3-) and nitrite-nitrogen (NO2-) oxidizing enzymes indicated that the CN(-)did not affect the expression and activity of ammonia monooxygenase (AMO); albeit, reduced the expression and activity of nitrate reductase (NaR) and nitrite reductase (NiR). Nevertheless, a slow decrease in NO(2)(-)was observed after the supplementation of CN(-)to the cultures, thus confirming the activity of NaR and the activation of the denitrification pathway by the CN-. These special characteristics of theAcinetobacter courvaliniiisolate, suggests its suitability for the treatment of wastewater containing multiple nitrogenous compounds in which CN(-)is present.