| Anaerobic granular sludge was trained under the condition of aeration to be aerobic granular sludge with the function of simultaneous nitrification and denitrification. Microorganisms like heterotrophic bacteria; nitrification and denitrification bacteria grew in the aerobic granular sludge, and cooperated and supported each other during reaction. The aerobic granular sludge became an ideal place for simultaneous nitrification and denitrification.With the aerobic granular sludge, the characteristics and reaction process, feature and distribution of microorganisms, the kinetic and mechanism of reaction, the generation and control of N2O were studied in a 2L reactor. Main research and corresponding results are described as follow from five aspects: i. Cultivation of aerobic granular sludgeAnaerobic granular sludge was changed to aerobic granular sludge under the condition of aeration after 93d cultivation. The aerobic granular sludge obtained had the function of simultaneous nitrification and denitrification. Over 90% COD and almost 98% NH4+-N could be removed during the reaction period with aerobic granular sludge, NO2~-N and NO3--N in effluent were not detected. Aerobic granular sludge had established the good reaction system of nitrification and denitrification. In a 6h reaction process, 73.6% COD was removed at 2h, COD degraded to 87mg/L after 3h, while the concentration of NO2~-N and NO3--N was decreased continually. The 6h reaction process showed that the aerobic granular sludge had strong ability of simultaneous nitrification and denitrification.The aerobic granular sludge obtained had the average diameter 2.26mm, the range of 2.1 ~2.8mm granular sludge was 60% of all sludge. STR was 22d, there were about 1.1 x 104 granular in the 1.5L reaction. The special surface of granular was 389m2/m3, the maximum sedimentation speed was 9cm/min, and the maximum affording force was 23.236N. In the reaction, MLSS was 8g/L, SV 15-28%, SVI 20~38ml/g. Observed under the microscope, itwas found that the granular sludge was a suitable place for the reaction of aerobic and anaerobic reaction, the surface structure of granular sludge was mainly tighten by coccus, and the internal had a lot of gaps grown by bacilli. ii. Growth characteristics of aerobic granular sludgeThe best suitable growth temperature of aerobic granular sludge for simultaneous nitrification and denitrification was 25-3 8 , the pH 7-8 and the DO 1 ~2mg/L. The affinity constants of aerobic granular sludge for ammonium and COD were less than 2mg/L and 100mg/L respectively. When the COD concentration and ammonium were over 1500mg/L and 400mg/L respectively, the consumption rates of COD and ammonium decreased correspondingly. With high ammonium concentration in broth, the midst products of nitrification, nitrite and nitrate, accumulated during the reaction that restricted the activity of aerobic granular sludge.Lungs model, fitted the experimental data best (R2 for COD0.9932, for NH4+-N 0.9916). The coefficients were Kt=111.1mg/L, a=0.836 for inhibition of COD consumption by ammonium, and Ki=103.1mg/L, a=1.08 for inhibition of ammonium oxidation by ammonium. During cultivation by fed-batch experiment with low concentration of ammonium (30mg/L), there were low nitrite and nitrate existed after reaction; with concentration of 200mg/L, nitrite and nitrate were 12 and 30mg/L in broth; and with concentration of 400mg/L, nitrite was 60mg/L in broth after 2h that restricted the reaction.With the adsorption experiment of COD, it was found that aerobic granular sludge could adsorb COD 56.7mg/gSS after 2h. Simultaneously, PHAs was accumulated in the bacteria in granular sludge, and it served as the electron donor for effective simultaneous nitrification and denitrification. iii. Microorganism distribution and mixing cultivation of aerobic granular sludgeAccording to the features of morphology, physiology and biochemistry of 29 bacteria separated from the aerobic granular sludge, it concluded that there were 5 Pseudomonas, 1 Nitrosomonas, 4 Nitrospira, 3...
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