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PhD Defense by Escandar Poorasgari

Escandar Poorasgari, Department of Chemistry and Bioscience, will defend his thesis on "Fouling of membrane bioreactor by soluble microbial products: contribution of adsorption, gel formation and gel compression".

Last modified: 11.11.2014


11.12.2014 kl. 13.00 - 16.00


"Fouling of membrane bioreactor by soluble microbial products: contribution of adsorption, gel formation and gel compression"


Wastewater treatment is an important part of environmental protection which is an issue of concern worldwide. So far, several treatment technologies have been developed among which conventional activated sludge (CAS) and membrane bioreactor (MBR) are the most common. In comparison with CAS, MBR produces less excess sludge and effluent of higher quality, and requires smaller foot print. However, MBR technology suffers from the problem of membrane fouling which is the reduction of the permeability due to deposition of substances of MBR sludge, foulants, on the membrane or within its pores. Fouling necessitates periodical physical and chemical cleaning which results in increased operational costs and reduced membrane life-time.

The foulants of MBR sludge are present in two phases: solid and liquid phase. The foulants of the solid phase are mainly sludge aggregates that form a porous cake layer on the gel layer. The foulants of the liquid phase are called soluble microbial products (SMP). According to the existing knowledge of the field, the SMP adsorb to the membrane, form gel layer on the membrane surface and play crucial roles in fouling of MBR systems.

The contribution of adsorption and gel formation to fouling of MBRs has not yet been well understood. Moreover, effects of physical-chemical parameters on gel layer fouling have not been investigated. The present research has been carried out to study contribution of adsorption of SMP and gel formation by SMP to membrane fouling and irreversibility of the fouling. Furthermore, it has been investigated whether the SMP gel layer properties are dependent on applied pressure, pH and ionic strength.

It was shown that both adsorption and gel layer formation occurred. While adsorption did not have a significant effect on permeate flux, gel formation was mainly responsible for permeate flux decline. It was observed that the gel layer was compressible and the gel compression was reversible. Permeability of the gel layer was dependent on pH and ionic strength. Filtration resistance of the gel layer increased and compressibility of the gel layer increased with increasing pH. Effect of ionic strength was more complicated than the effect of pH.


  • Associate Professor, Morten Lykkegaard Christensen, Department of Chemistry and Bioscience, Aalborg University, Denmark


  • Associate Professor, Donghong Yu, Department of Chemistry Bioscience, Aalborg University, Denmark
  • Professor, Ann-Sofi Jönsson, Department of Chemical Engineering, Lund University, Sweeden
  • Associate Professor, Birgir Norddahl, Institute of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern University



Section of Chemistry, Department of Chemistry and Bioscience


Fredrik Bajers Vej 7H, 9220 Aalborg Ø, Denmark (room: 2403, 2405, 2407, 2409)