Comparative study of free cyanide inhibition on nitrification and denitrification in batch and continuous flow systems

The differences of free cyanide inhibition on nitrification and denitrification responsible for nitrogen removal in an activated sludge process were investigated in both batch and continuous flow systems. In a batch system, free cyanide of 0.2 mg/L caused a distinct lag phase on nitrification in activated sludge, while denitrification was almost completely inhibited at 5.0 mg/L of free cyanide. However, the continuous exposure to the toxicity of free cyanide in a successive batch system progressively increased its toxicity, resulting in lowering the threshold level necessary to inhibit both nitrification and denitrification over time. Compared to the batch systems, the threshold level of nitrification and denitrification of the continuous flow systems were 100 and 20 times higher than that of the batch systems, and the threshold level of denitrification of the continuous flow system was 2 times higher than that of nitrification. Contrary to CN- removal efficiency of the continuous nitrification reactor being gradually decreased under higher CN- loading, the denitrification reactor provided a continuous CN- removal.