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.