Role and influence of extracellular polymeric substances on the preparation of aerobic granular sludge

• Aerobic granules were prepared in about 30–35 days through 3 phases.
• Increased EPS contents significantly contributed to the formation of granules.
• More EPS could be secreted by the microbes with appropriate nutrients.
• The survival of microbes was reduced during a low ratio of F/M environment.
• A negative correlation between the EPS contents and SVI was found.

Due to the important role of the extracellular polymeric substances in the formation of aerobic granular sludge, the variation of the EPS contents in the process of cultivation and that in the one running cycle time were studied in this work. Aerobic granules with diameters between 0.8 and 1.1 mm were obtained within 30–35 days. The results suggested that the increase of EPS contents significantly contributed to the formation of aerobic granules. A linear relationship between the EPS and SVI was also developed, and it revealed that the aerobic granules had good settling property when the EPS exceeded 200 mg/g MLVSS. Two mainly components of EPS, protein (PN) and polysaccharides (PS), could act as the endogenous food for the microbes during the starvation period. The survival of the microbial population was jeopardized when the F/M ration was below 0.5 g COD/g SS d.

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