| Aerobic granulation and properties of aerobic granules are studied in two sequencing batch airlift reactors. The reactors are running under different operational condition, such as organic loading rate, seeding sludge, carbon source, superficial air velocity and hydraulic cycle time, the conclusions are as follows.Under different organic loading, surface of aerobic granules formed by seeding anaerobic granules is covered lots of filamentous organisms. When organic loading rate are under 1.58 Kg/m3 dand 14.120 Kg/m3d, removal rate of COD, TN and TP is 90%, 80% and 90%, respectively. But specific gravity, settling ability and ratio of water containing are worse than that of seeded anaerobic granules.When activated sludge is seeded in reactor, specific gravity of aerobic granules is 1.025 and ratio of water containing was 96% while SVI is decreased from 126.12 ml/g to 28.16~33.486 ml/g, and oxygen consumed rated is 1.312 mg O2/(min·g). Removal rate of COD, TN and TP is 96%, 86% and 96%, respectively.The process of aerobic granulation is different when seeding with different sludge.The granulation process is: collided each another→adhered reversibly→adheredirreversibly→ microbial growth→granulated when activated sludge is seeded. Afterthen, in the role of hydraulic shear force, bacteria are contacted tightly each other and come into being aerobic granules. On the contrary, when anaerobia granules are seeded, aerobic granulation can be regarded as the process of bio-film growth on surface of the anaerobic granules. Since anaerobic bacteria in the anaerobic granules can not survive under aerobic condition, the inner zone of granules becomes hollow which lead to inferior properties of granules.The influencing factors on the stability of aerobic granules are studied in the reactors. Different superficial air velocities, such as 1.3 cm·s-1 and 2.6 cm3·s-1 are conducted in two reactors R1 and R2 respectively while sucrose acted as solo carbon source. Aerobic granules formed under the lower superficial air velocity are not stable because of heavy growth of filamentous organisms in Rl, but aerobic granules formed under high superficial air velocity are easier to reach maturity with SVI is 18.53ml· g-1 in R2. When sludge loading rate is below to 0.3 kg·(kg·d)-1 in R2, however, surface of aerobic granules began to grow filamentous organisms which lead to instability of aerobic granules. When acetic sodium acts as solo carbon source in reactor, it is found aerobic granulation is not well because floc sludge is dominant. But when mixed carbon source, such as sucrose and aceticsodium, are acted as carbon source, the stability of aerobic granules is improved distinctly.Granules size, VSS%, granules strength and specific gravity are reduced when prolonging hydraulic cycle time in reactors. Under 3h cycle time, diameter of granules is 1.5-2.0 mm, VSS is 92.08% and settling velocity is 36.78-42.71 m/h. But when diameter of granules is too large (>2mm), the settling ability of granules is worse for diffusive resistance of nutriments to inner zone of granules. Taking the consideration of all effective factors, it is proposed that the suitable size of granules was 1.0-1.5mm, so the optimize hydraulic cycle time is 6 h.Aerobic granules are a new biotechnology for simultaneous nitrification and denitrification. Nitrifying bacteria in aerobic granules are cultured separately using selected mediums. Growth properties and morphology of bacteria colonies under different condition are studied by controlling oxygen in culture medium. It is found that nitrifying bacteria is diverse in aerobic granules and they had different requirement for oxygen. The diversity of bacteria in aerobic granules is a premise of simultaneous nitrification and denitrification.
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