| With the acceleration of the urbanization process, wastewater discharge and pollution degree increased constantly in medium-small towns, rural areas and communities, which caused great environmental pollutions and ecological destructions. As a result, urging the biological treatment process developing along the trend of efficient integration and developing the efficient, integrated wastewater treatment process was imperative. The aerobic granular sludge method has been paid more and more attention to in recent years because of its higher settling performance, better biological activity, larger biomass, stronger anti-shock loading capability and so on, which could maintain a higher concentration of the micro-organisms in the reactor thus achieve the purpose of high efficient degradation. Researches on aerobic granular sludge which was mainly cultured in SBR reactors with high height-diameter ratio were mainly focused on its operation mode, nutrition supplies, aeration conditions at present, while the researches concerning the influence of fluid shear stress on the formation of granular sludge was rarely reported. As a key factor influencing the composition and stability of granular sludge, fluid shearing stress or called hydrodynamic conditions (flow field and shearing stress) played an important role in the attachment and self-fixing process of microbial.Secondary-flow Sequencing Batch Reacto(rSSBR)was developed in this research by optimizing the boundary conditions of SBR reactor. The synchronous experiments with both SSBR and SBR were carried out to analyze the morphology, characteristic of granular sludge, and the mass-transfer performance, waste-water treatment performance, stability of different reactors. Based on the analysis, the influence of hydrodynamic conditions (secondary flow field) on the formation of aerobic granular sludge and the mass-transfer, degradation performance of the reactor were studied, as well as the mechanism.â‘ Comparison on the characteristic of granular sludge in SSBR and SBR indicated that sludge characteristics was greatly improved in SSBR thus accelerated the granulation process by controlling the hydrodynamic conditions and optimizing the secondary flow field. And the better settling performance of SSBR was beneficial to the formation of aerobic granular sludge with high concentration, which was an effective way of realizing highly effective biodegradation.â‘¡Contrast experiments on SSBR and SBR reactors showed that the oxygen transfer rate increased so significantly in SSBR by optimizing the hydrodynamic conditions that the penetration depth of dissolved oxygen also improved greatly. As a result, nutrition supply to the central region of granular sludge was so ample that microorganism in the granular sludge would not get aging easily, which could stabilize the granular sludge system and improve the removal efficiency of organic compounds and organic nitrogen.On the base of the researches above,"high concentration flocculating aerobic granular sludge fluidized bed equipment"was developed and semi-industrial experiments were performed. 3 months'continuous operation proved that this equipment had higher biodegradation efficiency and could run stably. The experiment results showed that the MLSS in the equipment could reach up to 14g/L, which was 4 times of AA/O oxidation ditch(MLSS:3~4 g). When the hydraulic retention time (HRT) took one hour, the effluent COD concentration turned out to be 45mg/L, which could satisfy the national emission standards. While the HRT was 4 hours, effluent COD concentration turned out to be 23 mg/L, which was 4 times of AA/O oxidation ditch. Finally, the mechanism of stable operation for this equipment was analyzed. Based on the analysis, the"wrap-breakdown-rewrap"model was proposed, which provided a certain theoretical basis for the highly efficient degradation of floc aerobic granular sludge.
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