Insight into the role of exopolysaccharide in determining the structural stability of aerobic granular sludge

Extracellular polymeric substances (EPS) have a critical contribution to the stability of aerobic granular sludge (AGS), but the mechanism and details of EPS composition and function are far from clear. This work investigated the contribution of exopolysaccharide (PS) to maintaining the structural stability of AGS. The results revealed that PS hydrolysis induced by alpha-amylase, dextranase and cellulase significantly decreased the granular stability, whereas a substantial content reduction of extracellular protein (PN) was also observed. It was also found that hydrolysis of PS led to a decrease of sludge hydrophobicity, granular gel mechanical strength by 14.09 %, 38.67 %, respectively, and an increase of surface free energy by 49.59 %, which is not conducive to granular stability. Through fluorescent staining, existence of large amounts of PS and PN conjugates in EPS matrix was verified. It was proposed that these conjugates with PS as skeleton (PS-PN) dominate granular stability by affecting hydrophobicity interactions and hydrogen bonds system, which are two important parameters to gel properties, constituting a crucial finding of this work. This study offers an supplementation of EPS system theory and granular stability mechanism.

Automated summary

This study revealed the significant contribution of exopolysaccharide (PS) to maintaining the structural stability of aerobic granular sludge (AGS) by affecting hydrophobicity interactions and hydrogen bonds system, which are crucial parameters for gel properties. The hydrolysis of PS led to a decrease in sludge hydrophobicity, granular gel mechanical strength, and an increase in surface free energy, ultimately impacting the granular stability. Additionally, the existence of PS and PN conjugates in the EPS matrix was confirmed, proposing a new insight into the EPS system theory and granular stability mechanism.