Effect of influent substrate ratio on anammox granular sludge: performance and kinetics

Effect of influent substrate ratio on anammox process was studied in sequencing batch reactor. Operating temperature was fixed at 35 ± 1 °C. Influent pH and hydraulic retention time were 7.5 and 6 h, respectively. When influent NO₂^--N/NH₄⁺-N was no more than 2.0, total nitrogen removal rate (TNRR) increased whereas NH₄⁺-N removal rate stabilized at 0.32 kg/(m³ d). ΔNO₂^--N/ΔNH₄⁺-N increased with enhancing NO₂^--N/NH₄⁺-N. When NO₂^--N/NH₄⁺-N was 4.5, ΔNO₂^--N/ΔNH₄⁺-N was 1.98, which was much higher than theoretical value (1.32). The IC₅₀ of NO₂^--N was 289 mg/L and anammox activity was inhibited at high NO₂^--N/NH₄⁺-N ratio. With regard to influent NH₄⁺-N/NO₂^--N, the maximum NH₄⁺-N removal rate was 0.36 kg/(m³ d), which occurred at the ratio of 4.0. Anammox activity was inhibited when influent NH₄⁺-N/NO₂^--N was higher than 5.0. With influent NO₃^--N/NH₄⁺-N of 2.5-6.5, NH₄⁺-N removal rate and NRR were stabilized at 0.33 and 0.40 kg/(m³ d), respectively. When the ratio was higher than 6.5, nitrogen removal would be worsened. The inhibitory threshold concentration of NO₂^--N was lower than NH₄⁺-N and NO₃^--N. Anammox bacteria were more sensitive to NO₂^--N than NH₄⁺-N and NO₃^--N. TNRR would be enhanced with increasing nitrogen loading rate, but sludge floatation occurred at high nitrogen loading shock. The Han-Levenspiel could be applied to simulate nitrogen removal resulting from NO₂^--N inhibition.