The importance of liquid phase analyses to understand fouling in membrane assisted activated sludge processes—six case studies of different European research groups

In combination with wastewater treatment by activated sludge processes, micro- or ultrafiltration membranes can be used either for direct sludge filtration (membrane bioreactor concept) or as a polishing step after the settler (effluent filtration concept). In both applications, membrane fouling is a major issue. Recent research activities point towards the importance of soluble and colloidal material on membrane fouling in wastewater applications. Up to date no standardised methods for fouling determination, phase separation, or liquid phase analyses exist. In this paper, six independent research projects are presented. Wastewaters treated and research aims were basically unequal. Although starting from different angles, all groups finally ended up analysing the organic fraction in the effluent and activated sludge supernatant, respectively. Results of the presented case studies show the clear relevance of liquid phase constituents, either colloidal or soluble, with regards to membrane fouling. The analytical methods applied by the different research groups are presented and – where possible – compared. Giving the observed impact of liquid phase organic matter on membrane fouling, the paper is intended as a step towards a standardisation of possible analytical methods. The availability of such standards would allow direct comparison of different research projects and applications and help to create tools for trouble shooting in membrane assisted wastewater treatment.