| Nitrogen and phosphorous are the main pollutants that cause eutrophication of water body. However, traditional nitrogen and phosphorus removal processes exist some problems such as complex system, large footprint, high investment, and etc. Therefore, to explore the economic, efficient and energy-saving technology of biological nitrogen and phosphorus removal is a main focus in the field of wastewater treatment today. Compared with conventional activated sludge process, aerobic granular sludge not only has some unique advantages, such as high biological activity, good settling performance and strong resistance capacity, but also can achieve simultaneous nitrogen and phosphorus removal.In the experiment, a sequencing batch reator(SBR) was adopted to cultivate aerobic granular sludge rich in phosphorus accumulating organisms(PAOs). And through inducing, simultaneous nitrogen and phosphorus removal could be achieved in aerobic granular sludge. Effects of organic load and shear stress on aerobic granular sludge cultivation under the condition of low dissolved oxygen(DO), phosphorus removal characteristics of mature aerobic granular sludge, inducing nitrogen removal process and nitrogen and phosphorus removal mechanism of aerobic granular sludge were mainly studied in this paper. The major results were as follows:(1) Sodium acetate was used as the carbon source, ordinary floccus activated sludge was used as the inoculation sludge and organic load was used as control parameter. An operating mode that incorporated anaerobic-aerobic portions was utilized in SBR. Mature aerobic granular sludge was successfully cultivated under the conditions of low DO and the settling time of 30.minutes. When organic load was 0.482～0.986kgCOD/(m3·d), sludge granulation could not be achieved completely. When organic load was increased to 2.218-2.263kgCOD/(m3·d),, the sludge granulation was obtained rapidly at the beginning, then the large-size granular sludge broke up; When organic load was decreased to 1.15kgCOD/(m3·d) around, sludge granulation was achieved completely(2) DO during the aerobic period, organic load and the settling time were kept as 0.5～1.5mg/L,1.15 kgCOD/(m3-d) and 5 minutes respectively. Mature aerobic granular sludge was cultivated successfully in different shear stress (4.2N/m2,5.3 N/m2,6.5N/m2,7.7 N/m2) The results showed that within the range of 4.2～7.7N/m2, the larger the shear stress was, the denser the structure of cultivated aerobic granular sludge was, more regular the shape was and the stronger the biological activity was. When shear stress is between 4.2 and 6.5N/m2, the larger the shear stress was, the faster the sludge granulation process was and the larger the cultivated granular sludge size was. However, excessive shear force (7.7N/m2) would slow down the process of sludge granulation and the size of cultivated sludge particles would become smaller instead.(3) COD/PO43--P and sludge age are important factors of biological phosphorus removal. Within the range of 15-35, the larger COD/PO43--P was, the higher the average rate of releaseing phosphorus in anaerobic period, the average rate of absorbing phosphorus and the phosphorus removal rate would be. When the influent concentration of COD and PO43--P were 350 mg/L and 10 mg/L respectively, the best sludge age was 15d.(4) Regarding mature aerobic granular sludge rich in PAOs in SBR as the study subject, aerobic granular sludge which had simultaneous nitrogen and phosphorus removal capacity was induced successfully by increasing ammonia nitrogen load of the influent gradually. The removal efficiency of the aerobic granular sludge on NH4+-N, TN and PO43--P were 99.7%, 89.8% and 94.5% respectively.(5) Unique hierarchical structure of aerobic granular sludge provided different living environment for nitrifying bacteria, denitrifying bacteria, PAOs and denitrifying PAOs and made it possible for aerobic granular sludge to realize simultaneous nitrogen and phosphorus removal.
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