Comparison of typical nitrite oxidizing bacteria suppression strategies and the effect on nitrous oxide emissions in a biofilm reactor

In mainstream partial nitritation/anammox (PN/A), suppression of nitrite oxidizing bacteria (NOB) and mitigation of N2O emissions are two essential operational goals. The N2O emissions linked to three typical NOB suppression strategies were tested in a covered rotating biological contactor (RBC) biofilm system at 21 degrees C: (i) low dissolved oxygen (DO) concentrations, and treatments with (ii) free ammonia (FA), and (iii) free nitrous acids (FNA). Low emerged DO levels effectively minimized NOB activity and decreased N2O emissions, but NOB adaptation appeared after 200 days of operation. Further NOB suppression was successfully achieved by periodic (3 h per week) treatments with FA (29.3 & PLUSMN; 2.6 mg NH3-N L-1) or FNA (3.1 & PLUSMN; 0.3 mg HNO2-N L-1). FA treatment, however, promoted N2O emissions, while FNA did not affect these. Hence, biofilm PN/A should be operated at relatively low DO levels with periodic FNA treatment to maximize nitrogen removal efficiency while avoiding high greenhouse gas emissions.

Automated summary

In mainstream partial nitritation/anammox (PN/A) systems, suppressing nitrite oxidizing bacteria (NOB) activity and reducing N2O emissions are crucial goals. This study tested the N2O emissions associated with three NOB suppression strategies in a covered rotating biological contactor (RBC) biofilm system at 21 degrees C: low dissolved oxygen (DO) concentrations, free ammonia (FA) treatments, and free nitrous acids (FNA) treatments. Low DO levels effectively decreased NOB activity and reduced N2O emissions, but NOB adaptation occurred after 200 days. Periodic FA or FNA treatments effectively suppressed NOB, with FA treatment promoting N2O emissions and FNA treatment having no effect. Therefore, operating biofilm PN/A systems at low DO levels with periodic FNA treatment can maximize nitrogen removal efficiency while minimizing greenhouse gas emissions.