Effect of Shear Stress on Activated Sludge Granular in Sequencing Batch Reactor

The cultivation of aerobic granular sludge with the capacity of removing phosphorus was performed in the Sequencing Batch Reactor(SBR) using conventional flocculent activated sludge as seeding sludge and synthetic municipal wastewater. The results showed that the aerobic granular sludge had the good settling-ability, the high biomass retention and the regular structure with a diameter of 1.0 to 2.0mm, SVI of which was 20~22mL/g. Moreover, the effect of shear stress on granulation, morphology and bioactive of granules were all investigated. The results showed that within the range of 4.2~ 7.7N/m2 of shear stress, the lager the shear stress was, the denser, the more regular and the more bioactive of granules was. When shear stress is between 4.2 and 6.5N/m2, the larger the shear stress was, the faster the sludge granulation process 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. In addition, Aerobic granular sludge which had the capacity of removing nitrogen and phosphorus simultaneously was successfully induced by gradually increasing ammonia nitrogen concentration in the influent. The removal efficiencies of the aerobic granular sludge on TN and PO4-P were 89.8% and 94.5%, respectively. Key words-low DO; aerobic granular sludge; shear stress; the capacity of removing nitrogen and phosphorus simultaneously.