The performance of ANAMMOX (anaerobic ammonium oxidation) process with different operation strategies was investigated in two lab-scale upflow bioreactors. The results showed that the nitrogen removal rate of 3.78 kg·m-3·d-1 was achieved when the bioreactor was operated at high substrate concentrations with recirculation ratio of 1.07. However

it went up to 25.04 kg·m-3·d-1

which was 6.62 times higher than that above-mentioned

when the bioreactor was operated at relatively low substrate concentrations without recirculation. The operation strategy to run the bioreactor at relatively low substrate concentrations was far better than that to run it at high substrate concentrations. In the operation

ammonia could be a little excess over nitrite since the toxicity of ammonia was weaker than that of nitrite. The nitrite loading rate should be determined according to the capacity of nitrite conversion so as to avoid the nitrite inhibition from the overloading. When nitrogen-containing wastewater with a high concentration is treated

effluent recirculation can alleviate the nitrite inhibition or influent dilution can reduce the nitrite concentrations below the threshold value.