Foaming in membrane bioreactors: Identification of the causes

Michele Torregrossa, Gaetano Di Bella

Research output: Contribution to journalArticle

26 Citations (Scopus)


Membrane bioreactors (MBRs) represent by now a well established alternative for wastewater treatment.Their increasing development is undoubtedly related to the several advantages that such technology isable to guarantee. Nevertheless, this technology is not exempt from operational problems; among themthe foaming still represents an “open challenge” of the MBR field, due to the high complexity of phe-nomenon. Unfortunately, very little work has been done on the foaming in MBRs and further studies arerequired. Actually, there is not a distinct difference between conventional activated system and MBR: themain difference is that the MBR plants can retain most Extracellular Polymeric Substances (EPSs) in thebioreactor. For these reason, unlike conventional activated sludge systems, MBRs have experiencedfoaming in the absence of foam-forming micro-organisms. Nevertheless, the actual mechanisms of EPSproduction and the role of bacteria in producing foam in activated sludge in MBRs are still unclear. In thispaper, the authors investigated the roles of EPS and foam-forming filamentous bacteria by analyzingsamples from different pilot plants using MBRs. In particular, in order to define the macroscopic featuresand the role of EPS and filamentous bacteria, a Modified Scum Index (MSI) test was applied and pro-posed. Based on the MSI and the foam power test, the causes of biological foaming were identified interms of the potential for foaming, the quality and the quantity of the foam. The results indicated that theMBR foaming was influenced significantly by the concentration of bound EPSs in the sludge. In addition,the quantity and stability of MBR scum increased when both bound EPSs and foam-forming filamentousbacteria were present in the activated sludge.
Original languageEnglish
Pages (from-to)453-461
Number of pages9
JournalJournal of Environmental Management
Publication statusPublished - 2013

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Waste Management and Disposal
  • Management, Monitoring, Policy and Law

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