Cultivation of aerobic granular sludge with municipal wastewater and studies on its characteristics under the continuous flow

The aerobic granular sludge was cultivated successfully in a continuous-flow airlift aerobic granular sludge fluidized bed(CAFB),with low-concentration municipal sewage as the influent and flocculent activated sludge as the seeding sludge.The formation,characteristics and the biological diversity of the aerobic granules in the CAFB were investigated and analyzed.Experimental results showed that many dense and compact granules with diameter of 800-1 000 μm were formed as early as the 6th days operation.At the start-up stage,sludge volume index(SVI) decreased to 35 mL·g-1,the mixed liquor suspended solid(MLSS) concentration increased to 6 000 mg·L-1,and the mass fraction of extracellular polymeric substances increased significantly.The granules presented a good biological diversity and high biomass contents at the steady running stage.The aerobic granules were basically composed of coccid and bacillus as observed by the scanning electron microscope.A large number of voids and channels were found to be located on the surface of the granules.The removal rate of COD maintained at 70%-75% at the steady stage of CAFB running,and the effluent COD concentrations were 70 mg·L-1.At the 32nd day of operation,filamentous bacteria grew apparently and sludge bulking happened.Above results showed the CAFB aerobic granules formed rapidly,and performed a good ability on the pollutant removal.However,more work is necessary on the steady running of this novel bioreactor in the future.