1. Institute of Urban Water Management and Environmental Engineering, Ruhr-Universität Bochum, Bochum, Germany
2. Instrumental Analytical Chemistry, University of Duisburg-Essen, Essen, Germany
3. Centre for Water and Environmental Research (ZWU), University of Duisburg-Essen, Essen, Germany
4. Emschergenossenschaft/Lippeverband, Essen, Germany