Does denitrification via direct biological oxidation of ammonia to dinitrogen gas exist?

Abstract

To explore the possibility of directly biological oxidation of ammonium (NH4) to dinitrogen gas (N2) via oxygen (O2), the stoichiometric equations of the reaction were established via a thermodynamic method. Moreover, the yields of the microbials responsible for the possible reactions under different energy-transfer efficiencies were evaluated. The results indicated that, the direct oxidation of NH4 to N2 by O2 was an exergonic reaction, the microorganisms catalyzed this reaction were chemolithotrophs, and can obtain energy from this reaction for growth and synthesis. When energy-transfer efficiencies and sludge retention times were in the range of 20%–70% and 10–20 d, respectively, the microbial yields were in the range of 0.0225–0.2424 mg Cell/mg N. Compared with the known biological nitrogen removal processes, nitrogen removal via direct oxidation of NH4 to N2 has great advantages, for example, low sludge yield and low energy consumption. More efforts should be devoted to find the evidence of the existence of the direct oxidation of NH4 to N2 by O2.