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 (N-2) via oxygen (O-2), 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 NH(4)(+ )to N-2 by O-2 was an exergonic reaction, the microorganisms catalyzed this reaction were chemolith- otrophs, 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 NH(4)(+ )to N-2 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 NH(4)(+)to N-2 by O-2.