Operation of a nitrite-type airlift reactor at low DO concentration

Laboratory scale experiments were performed to evaluate the feasibility and potential of nitrite-type nitrification process with an airlift reactor having aerobic granular biomass. Oxygen limitation was selected as the main control parameter for inhibiting the growth of nitrite oxidizer and thus achieving only nitritation. To enhance granule formation, seeding of methanogenic anaerobic granules was used to serve as an initial carrier material. After 90 days of operation at low DO concentration of less than 1.0 mg/l, the maximum nitrite conversion rate of 2.6 g NO2-N/L/d could be achieved. During the continuing year-long stable operation, the granular mass of nitritation granules increased to about 15 g VSS/L with an average granule size of 0.7 mm. Nitrate-N concentration was observed to be below 10 mg/L during the whole operational period. From the results of the experiments, it is concluded that a granule-type airlift reactor with DO control is feasible for achieving stable nitritation.