1. a Wetsus, Centre of Excellence for Sustainable Water Technology , Agora 1, P.O. Box 1113, 8900 CC , Leeuwarden , The Netherlands
2. b Environmental Biotechnology Group, Delft University of Technology , Delft , The Netherlands
3. c Biofilm Centre, University of Duisburg–Essen , Duisburg–Essen , Germany
4. d Vitens , Lelystad , The Netherlands
5. e Membrane Process Technology Group, University of Twente , Enschede , The Netherlands