1. Department of Civil Engineering, Benha High Institute of Technology, P.O. Box 13512, Benha El-Gedida, Benha, Egypt (E-mail: t_elmitwalli@yahoo.com)
2. Institute of Wastewater Management and Water Protection, Hamburg University of Technology, Eissendorfer Strasse 42, D-21073, Hamburg, Germany (E-mail: moataz.shalabi@tuhh.de; c.wendland@tuhh.de; otterpohl@tuhh.de)