Nitrification rates in a saline medium at different dissolved oxygen concentrations

A kinetic study was carried out in a saline medium to assess the effect of O₂ on the two-step nitrification process: for the first nitritation step, 2–26 mg dissolved O₂ (DO) l^–1 was used and for the second nitratation step, 0.5–24 mg DO l^–1 was used. Nitritation rate was measured in the presence of sodium azide so as to inhibit nitratation. Ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacterial in the mixed culture were determined by 16 S rRNA hybridization. The affinity constants for oxygen O₂ of the AOB and the NOB were 1.66 mg O₂ l^–1 and 3 mg O₂ l^–1 respectively. The larger than the previously reported values of these constants might be due to the high salt content in the medium. High O₂ concentrations did inhibit the nitrification rate.