FACTORS AFFECTING NITRITE BUILD-UP IN NITRIFYING BIOFILM REACTOR

Abstract

Nitrite build-up in a nitrifying biofilm reactor for direct denitrification from the nitrite stage was investigated. At least three factors were found to influence the nitrite build-up: (i) the relative specific growth rates of Nitrosomonas to Nitrobacter, μ_Ns/ μ_Nb in the biofilm; (ii) the relative initial ratio between Nitrosomonas and Nitrobacter on the support surface, (M_ao)N_s/(M_ao)_Nb; (iii) the level of free ammonia, particularly at greater than 0.1 mg N/l that can be inhibitory to Nitrobacter. Results showed that without free ammonia inhibition, the first two factors determined the degree of nitrite build-up. The effect of (M_ao)_Ns and (M_ao)_Nb on nitrification kinetics were more significant than the specific growth rates of Nitrosomonas and Nitrobacter. By regulating effects of these three factors, extremely high concentrations of nitrite build-up could occur in a biofilm reactor. This offers a potential for achieving direct denitrification through a nitrate shunt.

Keywords:

• Nitrifying biofilm
• Nitrite build-up
• Free ammonia inhibition
• Nitrification kinetics
• Population dynamics

Acknowledgments