Foaming in membrane bioreactor: identification of the causes

The biological foaming was related to the metabolism of certain microorganisms that synthesize and excrete hydrophobic compounds. Recently, by the attention of many researchers the biological foaming in the MBR has attracted, because MBR foam has been also observed in the absence of foam-forming microorganisms, contrarily to conventional activated sludge systems. In this paper the authors investigate the role of EPS and filamentous bacteria analyzing different samples from different MBR pilot plants. In particular, in order to define the macroscopic features and the role of EPS and filamentous bacteria a modified Scum Index (MSI) test was applied. Further a multiple classification of SI was proposed, relating to effect of EPS or filamentous bacteria. The causes of biological foaming were identified in terms of foaming potential, foam quality and quantity, basing on the modified Scum Index and Foam Power test