Extraction method and structural and composition characteristics of extracellular polymeric substances in granular sludge from an enhanced biological phosphorus removal system

In this study, based on the granular sludge formation mechanism of "microsphere-collision-bonding," biological phosphorus removal granules were divided into the following three structural levels: submicron particles, microsphere particles, and mature granules. Therefore, extracellular polymeric substances (EPS) were classified into microsphere level extracellular polymers (MEPS) and granular level extracellular polymers (GEPS), which provided a novel approach to identifying the role of EPS in microbial aggregations of granular sludge. With regard to this sludge, compared with another three common and efficient methods for EPS extraction, the ultrasonic-cation exchange resin method effectively separated these two extracellular polymers based on the new classification paradigm of EPS. The results also showed that the contents of protein, polysaccharide and the total polysaccharides/total proteins (PN/PS) ratios in the MEPS were much higher than those in the GEPS. In addition, the MEPS contained higher molecular weight proteins than the GEPS. The ultrasonic-cation exchange resin method was used to extract EPS from granular sludge with different carbon sources to evaluate its versatility. The results showed that the variety and size of proteins were clearly different in the different carbon source feeds and this was demonstrated to be an efficient and reliable extraction method.