Enhanced nitrogen removal by partial nitrification-anammox process with a novel high-frequency micro-aeration (HFMA) mode: Metabolic interactions among functional bacteria

A novel high-frequency micro-aeration (HFMA) mode with aeration frequency of 15 times/h and DO concentration lower than 0.5 mg/L was proposed. Advanced partial nitrification-anammox (PN-A) performance was achieved in a two-stage sequencing batch reactor-integrated fixed-film activated sludge reactor with the HFMA mode. When treating wastewater with carbon/nitrogen ratio of 3, the abundance of NO₂⁻-N oxidation related genes decreased, and the genes carried out NO₃⁻-N reduction and carbon source consumption were up-regulated. These variations in microbial metabolism brought more NO₂⁻-N substrate for the subsequent anammox process, and consumed part of the accumulated organic matter and NO₃⁻-N. Thus, the HFMA conditions eventually promoted the expression of anammox bacteria with NH₂OH as an intermediate metabolite and the substance exchange activity of anammox bacteria. The changes in microorganisms lead to increase in the nitrite accumulation rate, nitrogen removal efficiency and abundance of anammox bacteria (16.34%, 18.71% and 5.92%, respectively).