[Granulation of completely autotrophic nitrifying sludge in sequencing batch reactor]

The formation of aerobic granular sludge was investigated by seeding completely autotrophic nitrifying sludge in sequencing batch reactors (SBR) using synthetic wastewater containing ammonia in the range of 120-650 mg/L under the loading rates of 0.48-3.60 kg/(m3 x d). The experimental results indicated that the granular sludge could be formed on day 22 in SBR by inoculating nitrifying sludge when ammonium loading rate was 0.48 kg/(m3 x d), temperature was 30 degrees C +/- 2 degrees C and the settling time was gradually decreased to 10 min. The size variation of granular sludge underwent three stages: stagnant, rapid increase and stable stages. The granules kept increasing in size to around 500 microm at rate of 12 microm/d and became stable on 43 days. The mature granules held regular shapes and clear outline. The granular sludge with diameter larger than 300 microm accounted for 74.6%, there was almost no flocculate sludge in the reactor. During the granulation process, the color of the sludge became yellow reddish from grey. There were great amount of bacillus and clump of EPS distributed on the surface of granular sludge.