Inhibition of Nitrite Oxidation During Nitrification: Some Observations

Abstract

Abstract A series of laboratory experiments were performed under controlled pH conditions and at room temperature to quantitatively study the inhibitory effects on Nitrobacter during nitrification. The results indicated that, in addition to the free ammonia (FA) concentration, the pH itself played an additive role in the inhibition of Nitrobacter. Reactors which were maintained at the same FA concentrations but at different pH levels exhibited different inhibition characteristics. It was also found that the acclimatization of Nitrobacter for an extended period of time may increase its FA tolerance limit from 0.1–1.0 mg/L cited in literature to 2.5 mg/L. Laboratory units containing less biomass (about 1000 mg/L) were more sensitive to FA inhibition than those with a higher concentration (1500 mg/L). A new concept of “recovery time” was introduced in this study to describe the microbial behaviour under inhibited conditions. The recovery time of Nitrobacter was found to depend on FA concentration, pH, time of exposure and biomass concentration.