Effect of salinity on nitrification efficiency and structure of ammonia-oxidizing bacterial communities in a submerged fixed bed bioreactor

•The effect of salt (NaCl) on biological nitrogen removal was studied.•Nitrification process is inhibited at high salt concentrations (⩾24.1g NaCl/L).•Ammonia oxidizing bacterial communities were studied by 454-pyrosequencing.•Only 5 OTUs of 42 OTUs were found at all salinities tested.•amoA sequences related to Nitrosospira disappeared at high salinity. The effect of salt (NaCl) on biological nitrogen removal and community structure of ammonia-oxidizing bacteria (AOB) was investigated in a submerged fixed bed bioreactor (SFBBR). Influent wastewater was supplemented with NaCl at 0 (control), 3.7, 24.1 and 44.1g/L, and the rate of ammonia removal efficiency was measured by ion chromatography. The structure of the AOB community was profiled by 454-pyrosequencing, based on the amplification of partial ammonia-monooxygenase subunit A (amoA) genes. Salinity did not inhibit nitrification at 3.7g/L, while ammonia oxidation activity significantly decreased and nitrite was consequently accumulated in the SFBBR when the salt concentration was ⩾24.1g/L. The sequencing of amoA genes revealed that many of the OTUs found in the control experiment were still present at the full range of NaCl studied, while concentrations of 24.1 and 44.1g of NaCl/L promoted the emergence of new OTUs phylogenetically related to AOB described in saline environments.