In order to assess the stability of nitrogen removal systems utilizing anaerobic ammonium oxidation (anammox), it is necessary to study effects of influent dissolved oxygen (DO) on anammox activity since effluent from nitritation process feed to anammox process. In this study, the effects of influent DO on anammox bacteria entrapped in gel carriers were investigated using continuous feeding tests. The tests were performed in duplicate to confirm the reproducibility and anammox activities were evaluated under different DO concentration of 0 from 5 mg/L in influent. These results suggested that the DO concentration in influent to anammox reactor must be less than 2.5 mg/L. In addition, it was shown that the effect of influent DO on the anammox reaction is reversible because fallen anammox activity by influent DO of 5 mg/L recovered when the influent DO concentration was decreased to less than 1 mg/L.
