Bio-kinetics of simultaneous nitrification and aerobic denitrification (SNaD) by a cyanide- degrading bacterium under cyanide-laden conditions

Abstract

A microorganism isolated and identified as Acinetobacter courvalinii was 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 of Acinetobacter courvalinii was investigated. It was found that CN- concentration of 1.9 to 5.8 mg CN-/L did not affect the growth of Acinetobacter 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 NO2- 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 the Acinetobacter courvalinii isolate, suggests its suitability for the treatment of wastewater containing multiple nitrogenous compounds in which CN- is present.