The effect of sodium chloride on the two-step kinetics of the nitrifying process.

Sodium chloride affects the transformation rate of several compounds in bioreactors. Most authors report a decrease in microorganism activity at increasing salt concentrations. In this work, a kinetic model that relates sodium chloride concentration with the rates of each step of the nitrification process is proposed; thus, the effect of sodium chloride concentration (0 to 60 g/L) on the nitritation and nitratation rates was separately studied. To carry out the independent study of each step, a combination of the respirometric method with sodium azide, an inhibitor of the nitratation step, was performed. The dot-blot hybridization technique with 16S rRNA-targeted probes was used to determine the ammonia-oxidizing and nitrite-oxidizing bacterial fraction, then it was possible to relate the culture's function with its biological composition. Rates of both steps were linearly reduced at increasing salt concentrations: the nitratation rate was more affected than the nitritation rate. Simulations carried out in a nitrifying sequencing batch reactor indicate that nitrite might accumulate at high salt concentrations. Sodium chloride exerts a reversible inhibition on ammonia oxidation and nitrite oxidation.