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.