1. Institute of Chemical Engineering, Bulgarian Academy of Sciences, Acad. G. Bontchev Str., Bl. 103, BG-1113 Sofia, Bulgaria
2. Institute for Water Problems, Bulgarian Academy of Sciences, Acad. G. Bontchev Str., Bl. 1, BG-113 Sofia, Bulgaria
3. Arbeitsbereich Gewaesserreinigungstechnik, Technical University of Hamburg-Harburg, Eissendorfer Str. 42, D-21073 Hamburg, Germany