1. Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 9,
8911MA Leeuwarden; P.O. Box 1113, Leeuwarden 8900CC, The Netherlands
2. Environmental Technology, Wageningen University, Bornse Weilanden 9, 6708 Wageningen; P.O. Box 17, Wageningen 6700 AA, The Netherlands