Study On Quorum Sensing Effects And Regulation In Anaerobic Granular Sludge

Anaerobic granular sludge is used in wastewater treatment system by its numerous advantages, but its long cultivation period has always been the constraint of application. It is necessary to develop a new rapid cultivating technology of anaerobic granular sludge. This study ascertained the spatial distribution of key signal molecules by investigating three types of anaerobic granular sludge from typical industrial wastewater plants. The effects of signal molecules on the variation of anaerobic granular sludge characteristics were investigated by adding corresponding signal molecules. Then the relationships between signal molecules and anaerobic granular sludge in different pH, organic loading shock and the imbalance of nitrogen supply were explored. Finally, a novel regulation based on the quorum sensing theory was developed to accelerate the granulation of anaerobic sludge. Main conclusions were drawn as following: (1)70-90%of diffusible signal factor (DSF) was distributed in Sludge phase. Auto-inducer-2(AI-2) in the Water phase accounted for over80%of the total amount. Moreover, more than half of short and medium acyl chain N-acyl-homoserine lactones (AHLs) tended to spread in aqueous water, while the long acyl chain AHLs were located to granular sludge. The physicochemical properties of signal molecules, such as molecular weight, solubility in water or organic solutions might mainly affect their distributions.(2) The effects of three kinds of signal molecules on the main characteristics of anaerobic granular sludge were investigated by adding corresponding signal molecules. N-hydroxybutanoyl-homoserine lactone (C4-HSL) played a positive role in the synthesis of loosely bound (LB) extracellular polymer substances (EPS) in anaerobic granular sludge, not in the tightly bound (TB) one. C4-HSL would focus on promoting the content of protein (PN), and the degree of promotion was determined by the C4-HSL concentration. Moreover, AI-2played a positive role in the synthesis of LB-PN, TB-PN and LB-PS. However, the inhibition of DSF for EPS secretion was mainly concentrated on the synthesis LB-PN, but also on LB-PS and TB-PN to some extent. Then the relative hydrophobicity (RH) would decrease as EPS content decreasing.(3) The effects of signal molecules on anaerobic granular sludge under different environment were investigated. The results showed that the differences of EPS synthesis in different pH were not regulated by AHLs, but mainly by AI-2. The inhibition of DSF on the synthesis of EPS was insignificant. In the neutral and weak alkaline media, the combining regulation of increasing AI-2content and decreasing DSF content enhanced RH and granular strength in granular sludge, which made granular have a greater diameter and a more glossy granular shape. Whereas, the decreasing AI-2content and increasing DSF content in acid medium made a decrease in RH and granular strength, resulting in the degeneration of anaerobic granular sludge.(4) In two and three times organic loading rate (OLR) shock, the content of C4-HSL and N-3-oxo-hexanoyl-homoserine lactone (3-oxo-C6-HSL) decreased, but N-hexanoyl-homoserine lactone (C6-HSL) content increased followed by the OLR shocking and then decreased with the restoring OLR. The content of AI-2had a gradual decrease with the OLR shock and a rapid increasing at the end of shocking. The variation of DSF content was opposite to that of AI-2. In two times OLR shock, both of C6-HSL and AI-2played a role in promoting the synthesis of LB-and TB-EPS to reducing the negative impact from OLR shock. Three times OLR shock would improve DSF content, which would make a decreasing of PN to adapt the harsh environment. In above OLR shocks, the combination of AI-2and DSF made a decline of RH, granular strength and diameter in granular sludge. (5) With nitrogen supply of carbon/nitrogen (C/N)=200:1and200:20, the content of AHLs increased at first and decreased afterwards, and DSF content had an increasing change which was quite different with that of AI-2. In the nitrogen eutrophic reactor, the combination of C4-HSL, AI-2and DSF made an increase of LB-EPS secretion, which contributed to maintain the stability of granular structure. Whereas, in nitrogen unbalanced reactors, the regulation of AI-2and DSF made granular sludge degenerate.(6) According to the above results, a novel regulation method designed by the quorum sensing theory was developed to accelerate the granulation of anaerobic sludge. Increasing the content of AI-2in anaerobic sludge would promote the synthesis of PN and PS, improve RH and sludge diameter, and accelerate the granulation of anaerobic sludge. The same acceleration was found with the regulation of C4-HSL, but its promoting effect was weaker than that of AI-2in this study.