[Study on the stratification components of extracellular polymeric substances (EPS) in activated sludge and their variation characteristics in physicochemical properties].

To study extracellular polymeric substances (EPS) in activated sludge, EPS were extracted by cation exchange resin (CER) method as the total EPS, and stratified through centrifugation and ultrasound into three fractions: slime, LB-EPS and TB-EPS from the outside to the inside. The contents of proteins (PN), polysaccharides (PS) and DNA were determined separately. Furthermore, their variation characteristics in physicochemical properties along with the solution conditions were also investigated. Results showed that the maximum contents of PN, PS and DNA were found in the TB-EPS fraction. The hydrophilic components of the total EPS and its fractions had a higher concentration than the hydrophobic components, and PN showed a higher hydrophobicity than PS. The PS/PN ratio had a great influence on Zeta potentials and isoelectric point values of EPS. That is to say, the greater PS/PN ratio of EPS was, the smaller Zeta potentials for the total EPS or its fractions and the higher isoelectric point values for EPS fractions were. All Zeta potentials of EPS solutions presented a general decrease trend with increasing pH. The corresponding isoelectric point values were 2.9 for the total EPS, 2.2 for the slime, 2. 3 for the LB-EPS and 1.3 for the TB-EPS, respectively. The increase in ionic strength resulted in the tendency of straight climb with the increase in the conductivity of EPS solutions, while the corresponding Zeta potentials tended to reach stable negative values after a rapid increase. In addition, when temperature went up (<40 degrees C), the apparent viscosity of EPS solutions decreased, then gradually kept unchanged in the range from 40 degrees C to 60 degrees C.