1. Wetsus, Centre of Excellence for Sustainable Water Technology, Agora 1, P.O. Box 1113, 8900 CC Leeuwarden, The Netherlands, Sub-Department of Environmental Technology, Wageningen University, Bomenweg 2, P.O. Box 8129, 6700 EV Wageningen, The Netherlands, and Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, P.O. Box 8038, 6700 EK Wageningen, The Netherlands