Influence of high partial pressure of carbon dioxide and/or oxygen on nitrification

The advent of new intensive wastewater treatment processes with high rates of solution of oxygen, such as the oxygen activated‐sludge process and the Deep‐Shaft process, implies that there will be conditions of high concentrations of carbon dioxide and oxygen in the mixed liquor. These processes, as operated, have problems in maintaining nitrification. To determine how the above conditions affect the nitrifying bacteria, other than by reducing the pH, a mixed culture of nitrifying bacteria was maintained on a synthetic substrate in a computer‐controlled chemostat at constant pH and temperature, with different proportions of carbon dioxide and oxygen in the aeration gas. The specific growth rate of the ammonia‐oxidising bacteria was independent of the concentration of carbon dioxide in the gaseous phase when this was between 0.03 and 2.0%. The ammonia‐oxidising bacteria were initially inhibited by high partial pressures of oxygen but eventually became acclimatised and retained this property, even when grown for several generations at lower partial pressures.