The final cyanide reduction increased when initial cyanide concentration was increased (Table 2). Cyanide reductions of 56%, 58%, and 65.3% were obtained corresponding to initial NaCN concentrations of 50, 100 and 150 mg l−1 respectively. This is in agreement with Fisher et al. [20] who observe increased NH3 and CH4 at NaCN concentrations of up to 5 mM indicative of increased cyanide reduction. The rate of removal seems to be dependent on the initial NaCN concentration. When the concentrations increased from 50 to 150 mg l−1, the rate of cyanide removal was found to increase from 0.4 to 1.5 mg l−1 h−1. In addition, rate of cyanide removal was observed to be faster when the cells are at their exponential growth phase (6–30 h) as compared to when the cells are at their stationary phase (over 36 h). This suggests that rate of cyanide removal is linked to the metabolic activity of A. vinelandii.