Effect of pH and nitrite concentration on nitrite oxidation rate

► Respirometric experiments are a reliable method to determine the effect of pH and substrate concentration on NOB activity. ► Nitrite oxidation rate is clearly affected by pH value. pH values below 6.5 caused the complete inhibition of NOB. ► High pH values did not affect NOB activity, (similar activity was measured at pH values from 7.5 to 9.95). ► The sigmoid function proposed to represent the pH inhibition was able to accurately reproduce the experimental results. ► The NOB growth rate depends on TNO2 concentration but does not depend on FNA concentration.