Nitrifying microorganisms in fixed-bed biofilm reactors fed with different nitrite and ammonia concentrations

Nitrifying bacteria and archaea were fed in fixed-bed biofilm reactors with different nitrite and ammonia concentrations in synthetic and real wastewater. During high nitrite concentrations ( ρ ( NO 2 - ) = 5–10 mg/L), an increase in the abundance of Nitrobacter species was detected with fluorescence in situ hybridization (FISH), while Nitrospira species disappeared to a large extent. During high ammonia concentrations ( ρ ( NH 4 + ) = 60–80 mg/L), a slight increase in ammonia-oxidizing bacteria was obtained, while the abundance of archaebacteria remained unchanged. Lab-scale reactors showed a similar nitrifying microbial population as reactors fed with real wastewater. However, increased abundances of Nitrospira species as observed in wastewater reactors and in the wastewater trickling filters could not be found in the laboratory reactors.