Study on simultaneous short-cut nitrification-denitrification for nitrogen removal in wastewater with low C/N ratio

This study employed a single-stage aerobic sequencing batch reactor (SBR) to establish a simultaneous short-cut nitrification-denitrification (SSND) system, addressing the denitrification challenges in wastewater with low carbon-to-nitrogen (C/N) ratios. By controlling low dissolved oxygen (DO, 0.3-0.5 mg/L) and employing a strategy of gradually increasing influent nitrogen loading, short-cut nitrification was rapidly initiated within 18 days, achieving a nitrite accumulation rate exceeding 95%. Under conditions of an influent C/N ratio of 2, chemical oxygen demand (COD) of 1000 mg/L, and total nitrogen (TN) of 500 mg/L, the single-stage aerobic (O) mode demonstrated superior denitrification efficiency compared to the A/O mode, achieving COD and TN removal rates of 84.2% and 68.9%, respectively. Microbial community analysis revealed successful directed succession of functional bacterial communities: ammonium-oxidizing bacteria (Nitrosomonas) were effectively enriched (abundance increased to 11.10%), while nitrite-oxidizing bacteria (Nitrospira) were effectively suppressed (abundance <0.1%); Functional denitrifying bacteria (Thauera genus) emerged as the dominant genus (30.58% abundance). These bacteria undergo a 'saturation-starvation' cycle, utilising intracellular poly-β-hydroxybutyrate (PHB) accumulated during the anaerobic phase as an endogenous electron donor to drive simultaneous denitrification during the aerobic phase. Additionally, the study revealed that under carbon-limited conditions (C/N = 1), environmentally induced autolysis and extracellular polymer secretion occur, explaining fluctuations in effluent COD. This research provides theoretical support for applying the SSND process to treat low C/N wastewater.