Exploring the optimized strategy in the nitritation-anammox biofilm process for treating low ammonium wastewater

The main challenge for achieving the simultaneous nitritation, anammox and denitrification (SNAD) process is to optimize the concentrations of nitrite and dissolved oxygen (DO). This study explored the performance of SNAD biofilm reactor under three operational strategies. At Stage 1, 2 and 3, the average concentrations of DO were 0.7, 2.7 and 5.2 mg/L, respectively. The peak concentrations of NO₂^--N in the sequencing batch reactor (SBR) cycle were 5.3, 6.0 and 2.7 mg/L, respectively. The average removal rates of total inorganic nitrogen (TIN) were 0.30, 0.42 and 0.22 kg N/m³/d, respectively. Protein (PN) was the dominant extracellular polymeric substance (EPS) content on the SNAD biofilm. The PN concentration remained stable while the polysaccharide (PS) concentration changed rapidly under different operational strategies. High-throughput sequencing analysis indicated that high DO and long aeration period condition could lead to a slight decrease in the abundances of denitrifying bacteria and anammox bacteria.