| In order to investigate the effects of decreasing settling time and biofilm on the rapid start-up of aerobic granular sludge reactor for nitrification, the real domestic wastewater was treated in three sequencing batch reactors (SBR, named as R1,R2 and R3) and one sequencing batch airlift reactor (SBAR, named as R4). After decreasing the settling time from 20 min directly to 2, 4 and 2 min respectively in R1, R2 and R4, for the reason that the selective pressure of settling velocity was so strong that the activated sludge was all washed out of the reactors, the three SBRs lost their function of treating wastewater. Then the biofilm grew on the walls of the three reactors, and lots of soft granular-like sludge appeared in the reactors, 35～40 days later. The biofilm made the effluent ammonia of R1, R2 and R4 lower than 1 mg/L. The soft granular-like sludge was not the aerobic granular sludge, but there were lots of rotifers both around the soft granular-like sludge and the aerobic granular sludge. The phenomena showed that aerobic granular sludge was one type of biofilm. In R3 the settling time was shortened gradually from 20 min to 8, 6, 5 and 4 min. When the settling velocity was 10 cm/min, the activated sludge began to granulate, and when the settling velocity reached 12 cm/min, the aerobic granular sludge became dominant in the reactor, but the sludge floc coexisted with aerobic granular sludge. It took 33 days to cultivate aerobic granules in R3. The average diameter of the aerobic granular sludge was 0.5 mm, the ratio of aerobic granular sludge to sludge floc by weight was 2∶1, and the ammonia oxidized rate of aerobic granular sludge was 5 times as the sludge floc's. |
