Comparison between two anammox fiber fillers under load impact and the effect of HCO₃ ^- concentration

Based on the establishment of a stable anaerobic ammonia oxidation treatment system in 100 days, the impact resistances of two different anammox fiber fillers (the curtain filler: R1 and the bundle filler: BR) were compared. Furthermore, the effect of HCO₃ ^- concentration on the bundle filler system was also investigated, the results have shown that the activity of the two anammox fiber fillers was not inhibited when the NO₂ ^--N concentration was lower than 750 mg L^-1 (FNA = 0.085 mg L^-1), while it was significantly suppressed at 900 mg L^-1 (FNA = 0.118 mg L^-1). However, the two fiber fillers could be recovered and exhibit a good impact resistance reduction of the substrate concentration. On day 95, the structure of the bundle filler was more conducive to the stable attachment, proliferation, and aggregation of anammox bacteria. Dominant anammox bacteria in both the curtain and bundle fillers were Candidatus Kuenenia, which accounted for 25.9% and 35.9% of the total population, respectively. When the influent HCO₃ ^- concentration was 900 mg L^-1, the bundled fiber filler had the highest total nitrogen (TN) removal efficiency, which reached 89.0%. Even though it was inhibited under 2000 mg L^-1 of HCO₃ ^- concentration, the reactor was able to recover within one week by reducing the substrate concentration. In addition, the HCO₃ ^- inhibition mechanism was independent of pH, which resulted in high FA content.