Abstract:Stable operation of partial nitritation reactor by using ORP online monitoring equipment and the effluent satisfied the anammox process were studied in continuous flow reactor. The results showed that fluctuation of ORP value was mainly caused by the fluctuation of DO concentration, when the ratio of nitrite and ammonia, pH and temperature were constant in the reactor. In partial nitritation system, the ratio of nitrite and ammonia was greater than 2.1when the ORP value was greater than 250mV, which didn’t satisfy the ANAMMOX process demanded. The ratio of nitrite and ammonia was oscillating between 1.2 and 1.3when ORP value was controlled at 150mV. The ratio of nitrite and ammonia was oscillating between 0.9 and 1.06when ORP value was controlled at 120mV. The results also showed that the ratio of effluent nitrite and ammonia was oscillating between 1.1 and 1.3 with the influent ammonia concentration increased from 300mg/L to 813mg/L when ORP value was controlled at 150mV. However, increased free ammonium (FA) concentration inhibited ammonia-oxidizing bacteria activity. Sensitivity and accuracy of ORP were better than DO monitoring equipment as indicators to controlling partial nitritation reactor in low oxygen environment.