Impact of free ammonia on anammox rates (anoxic ammonium oxidation) in a moving bed biofilm reactor

► The free ammonia FA on nitrogen removal rate (NRR) was investigated in anammox MBBR. ► FA had a significant inhibitory impact on NRR when exceeded 2 mg N/L. ► FA had greater effect on NRR than pH alone within pH range of 7.0-8.0. ► NRR was not inhibited by load changes when FA was low. ► Nitrite up to 120 mg N/L resulted in higher NRR under low FA concentrations.