Ammonium load determines the performance of a continuous nitritation process and the related microbial communities even under excesses of O2 supply

Background Partial oxidation of ammonium to nitrite, process known as nitritation, has important advantages over complete nitrification, including energy savings due to a reduced aeration, a lower organic carbon requirement for denitrification, a reduced production of sludge, and the potential use of nitrite in anammox and anoxic biogas purification technologies. Dissolved O-2 (DO) concentration commonly has been regarded as the most important parameter to be controlled for achieving a successful nitritation process. Results The present study showed that setting average DO values below 1 g O-2 m(-3) was insufficient to achieve a high and stable nitritation at ammonium loading rates between 2.5 to 5.1 g N-NH4+ m(-3) h(-1). Under these conditions, the predominance of nitrite oxidizing bacteria (NOB) resulted in ammonium oxidation selectivity to nitrite from 5.2 +/- 3.6% to 42.8 +/- 21%. Increasing the ammonium loading to 10.1 gN-NH4+ m(-3) h(-1) together with an average DO value of 0.9 +/- 0.6 gO(2) m(-3) resulted in an ammonium oxidation efficiency of 94 +/- 1.1% and ammonium oxidation selectivity to nitrite >90%. Conclusion Continuous nitritation was achieved in a single reactor provided with an easy-to-implement aeration strategy. The ammonium loading rate was the most important parameter to be controlled, which inhibited NOB above a threshold value. NOB inhibition was mediated mainly by free nitrous acid, and by free ammonia to a lesser extent. Increasing the ammonium loading rate led to an enrichment of ammonium oxidizing bacteria of the Nitrosomonas genus. (c) 2022 Society of Chemical Industry (SCI).

Automated summary

This study showed that controlling the ammonium loading rate is the most important parameter for achieving efficient and stable nitritation. Continuous nitritation was achieved by using an easy-to-implement aeration strategy.