Characteristics Of Anoxic Granular Sludge Cultivated In SBR

More attention has been paid on granular sludge because of its high activity and settling ability. Experiment was carried out to investigate the physicochemical properties and the interspecies cooperation of species in anoxic granular sludge cultivated with synthetic wastewater. The results were showed as follows.(1) Anoxic granular sludge can be successfully cultivated in SBR through hydraulic selection. The COD and NO_X-N removal rate was higher than 80% and 98% respectively in stable running. The mean wet density of anoxic granular sludge was 1.003-1.020 g/cm~3, and the MLVSS/MLSS ratio was 54%～84%. The mean settling velocity was 38.89～43.3m/h, showing better settling ability. The content of calcium was between 11%～25%, but the content of iron was less between 0.1%～0.3%.(2) The diffusion of microorganisms and its effect on the denitrified activity was studied to discuss interspecies cooperation of species in anoxic granular sludge. The result showed that when C/N ratio was 4.5, the interspecies cooperation in small granules (the average diameter was 0.5mm) had certain function in denitrification. However, this function could not make the intermediate nitrite be removed as soon as produced. When C/N ratio was 6, the denitrified velocity of granular sludge was higher than that of flocculent sludge, and the maximum nitrite concentration accumulated was obviously less, which showed great interspecies cooperation of species in granular sludge. When nitrate concentration was 80mg/l, the interspecies cooperation in big granules (the average diameter was 2.0mm) would greatly improve the denitrified activity.(3) The microorganisms of anoxic granules were observed in scanning electron microscope (SEM). It indicated that the microorganisms in the surface were mainly short bacillus and arrayed closely while the surface was not smooth. There were less bacteria inside the sludge, the microorganisms were mainly bacillus but arrayed not closely as that in the surface of granules. There were holes and cavities on surface and interior, which was the tunnel of nitrogen produced in denitrification.