The role of EPS in fouling and foaming phenomena for a membrane bioreactor

•Low content of foam-formation microorganisms was found.•There is a possible transfer of the EPS from the mixed liquor to the foam.•We found a good correlation between fouling and EPS and foaming and bound EPSs.•Fouling rate decreases with the foam formation.•In UCT-MBR plants the foam can be formed even without foam-former bacteria. In contraposition to conventional activated sludge processes, the foaming phenomenon in membrane bioreactor (MBR) is still in its infancy. On the other hand, although several studies have been carried out for better understanding the fouling phenomenon in MBR there are still some gaps in the up-to-date knowledge. The extracellular polymeric substances (EPSs) may have a primary role in fouling and foaming phenomena which in turn can be crucial for MBRs. The aim of this study is to detect a possible relationship that EPSs may have with fouling and foaming in an MBR for wastewater treatment. Foaming phenomenon is monitored by performing specific foam-tests: Foam Power, Scum Index, Foam Rating and filamentous abundance. Results show a high correlation between fouling vs EPS and foaming vs bound EPSs. A relationship between foaming and fouling was also found: in general, when foaming occurred the fouling rate decreases because the EPS bound remained trapped in the floating scum.