Fouling property and interaction energy with EPS membrane in normal sludge and bulking sludge

Extracellular polymeric substances (EPS) are the major substances leading to membrane fouling, and the EPS collected from different sludges have different characteristics. Therefore, characterization of the fouling property of EPS in normal sludge and bulking sludge (NS-EPS and BS-EPS) is important. Results from this study showed that the fouling rate of bulking sludge was much higher than that of normal sludge, and the EPS concentration and the ratio of protein/carbohydrate (P/C) of bulking sludge ((172.9±10.4) mg·g^-1 and 2.26, respectively) were also higher than the counterpart of normal sludge ((95.9±6.6) mg·g^-1 and 1.97, respectively). In addition, adsorptive fouling experiment was carried out to identify different EPS fouling properties between normal sludge and bulking sludge, and the interaction energy between the membrane and EPS was calculated based on the extended Derjaguine-Landaue-Verweye-Overbeek (XDLVO) theory. The result indicated that the membrane with EPS had a negative total energy, indicating self-adsorption as EPS approached the membrane. The energy between BS-EPS and membrane (-63.943 mJ·m²) was higher than that between NS-EPS and membrane (-56.366 mJ·m²), indicating stronger adsorption of BS-EPS than NS-EPS. The energy barrier of NS-EPS and BS-EPS were 8.89 kT and 7.51 kT, respectively, which showed that the NS-EPS had a strong repulsion force than BS-EPS, and BS-EPS was easier to attach to the membrane and led to membrane fouling.