| Microbial populations exit in biological wastewater treatment systems as free or aggregated cells, such as flocs and granules. Self-immobilization of microorganisms into aggregates or granules is a process that has been exploited for biological treatment of municipal and industrial wastewaters. From microscope, we can see that activated sludge were different from aerobic granules which were regular in shape and yellow in color and have a mean diameter between 0.5~5 mm. In recent years, researchers have given more interests in it because of its advantages such as regular, dense and strong microbial structure, good settling ability, and high biomass retention, tolerance to high organic loading rate/toxic shocks and synchronous nitrogen and phosphorus removal. Aerobic granules sludge has been cultivated by seeding activated sludge and anaerobic granules under different operational conditions before. But how to cultivate aerobic granules in a very short time and the mechanism of its formation are still puzzling.The cultivation of aerobic granules in three sequencing batch reactors (SBRs) by seeding activated sludge (R1), 15% mature aerobic granule sludge (R2) and 15% anaerobic granule sludge (R3) was investigated respectively using glucose-based wastewater. And the other objective of this study was to evaluate the role of extracellular polymeric substances (EPS) in aerobic granulation. Performance of EPS in granulation process, as well as Relative Hydrophobicity (RH) and proteins (PN) and polysaccharide (PS) of EPS in aerobic granules was discussed in this study. This work could be helpful in the development of aerobic granule-based systems for full-scale application.Over all, formation of aerobic granular sludge was shown in three SBRs with different seed sludge. Results of this study provided useful information on aerobic granulation in SBR.Aerobic granule sludge can be cultivated in a short time(20d) by seeding 15% mature aerobic granule sludge,this time of its cultivation was much shorter than in R1(60d)and R3(40d), and this way to cultivate aerobic granules sludge hasn't been reported yet. Formation of aerobic granule sludge was the combined action result of many mechanisms including self-agglomerate, crystal nucleus theory and filamentous bacteria enlace theory. EPS must play a positive role in the granulation of aerobic granules sludge.During the granulation period, content of PN increased a lot, its vaule changed from 20 to about 120, and content of pN in R2 increased faster than the other two reactors. At the same time, PN/PS ratio increased also, its vaule increase from 2 to about 5.There was a positive correlation between PN/PS ratio and RH (0.9325, 0.9125 and 0.9482 respectively). Moreover, PN/PS ration has good positive correlation with FA (0.959, 0.9357 and 0.9001 respectively). Increase of PN/PS ratio and RH could change the surface property of sludge, thus promote the cell coagulation and keep the structure of granules, and then further favoring aerobic granulation.Content of EPS and the exudation of EPS can be enhanced by seeding part of aerobic granules as seed sludge, the RH increased accordingly, and granules will formed in a short time.
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