Study Of Key Component In Extracellular Polymeric Substances During The Formation And Stability Of Aerobic Granular Sludge

The aerobic granular sludge is a class of microbial aggregates with compact physical structure and excellent settleability. Extracellular polymeric substances(EPS), as major compents of aerobic granular sludge, plays an important role in the formation and stability of aerobic granule. As the limitation of EPS extract and analytical methods, it's difficult to analysis the main EPS components and reveal the mechanism of aerobic sludge granulation. Based on the comparison of different EPS extraction methods for microbial aggregates, three-dimensional fluorescence spectroscopy (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the key components of EPS during the formation and stablility of aerobic granular sludge. Main conclusions were as follows:1,In view of the different effectiveness of various methods for EPS extraction from flocs sludge, unstable and stable aerobic granular sludge,3D-EEM was applied to investigate EPS extract efficiencies of cation exchange resin (CER), Sulfide, CER combined Sulfide, Formamide combined NaOH and Heat methods. It was found that the cells was negligibly broken to all of the extract methods. EPS concents extracted by Formamide+NaOH and Heat methods were higher than those by CER, Sulfide and CER+Sulfide methods, which suggested that Formamide+NaOH and Heat method had a higher EPS extraction efficiency. Analysis of 3D-EEM revealed that the EPS components extracted by CER, Sulfide and CER+Sulfide methods were incomplete, and Formamide+NaOH method, which could not effectively extract aromatic protein-like, was not suitable for the following analysis of sludge EPS composition. In contrast, the Heat method, which could fully extract EPS components including aromatic protein-like, fulvic acid-like and visible humic acid-like, was the best EPS extraction method for microbial aggregates.2, The results of sludge EPS analysis during aerobic sludge granulation using 3D-EEM showed that the response values of fluorescence peak B, D and F (Ex/Em=220-230/358.5-364,280-290/360-368,230/308.5) which represent aromatic protein-like gradually increased along with sludge granulation, and it's found that tyrosine protein-like(peak F, one of the aromatic protein-like) was enhanced granular sludge. The response value of fluorescence peak C (Ex/Em=350-360/445.5-452.5) which represent humic acid-like firstly increased and then decreased to a stable value, it's speculated that humic acid-like also favor microbial aggregates. Further analysis with FTIR indicated thatβ-sheet protein (1650-1640cm-1) and aspartic acid (1400cm-1) existed in the whole sludge granulation, and their variation tendency was consistent with PN content. The enrichment of tyrosine protein-like (1517cm-1) was also found in mature granule, and it's further confirmed its importance in the granular stability. In addition, the variation of absorption band between 1200-1000cm"1 which represent polysaccharide demonstrated that the structural shift of polysaccharide favors the aerobic sludge granulation and the mechanism about it need further research.3. The analysis of stable-and unstable aerobic granule EPS showed that the PN and PS contents of unstable aerobic granule significantly increased compared to the stable granule, but it's worth noting that aromatic protein-like (Ex/Em=220-230/342-368.5,230/308.5) was greatly decreased, which comfirmed the importance of aromatic protein-like in maintaining structural stability of aerobic granular sludge. Futhermore excessive humic acid-like (Ex/Em=360/447.5-452) would result in the loss of granular stability. FTIR results demonstrated that the existence of tyrosine protein-like(1517cm-1) and the structural shift of polysaccharide(1200-1000cm-1) played a critical role in the formation and stability of aerobic granule, and they are the key EPS components of aerobic granular sludge.