Suspensions can be conditioned by treatment in a standing ultrasonic field. This increases the efficiency of a following solid-liquid separation step. This project, supported by BMBF, investigates the application of ultrasound in the treatment of waterwork sludges. These sludges and sludge containing waters often have poor thickening or dewatering properties. The use of ultrasound is an alternative to conventional methods. It works without chemicals and thus does not increase the waste volume. Experiments in batch- and continuous flow systems show: The treatment of sludge containing filter backwash water is effective with a frequency of 2 to 3 MHz. The separation efficiency is up to 96%. For the thickening of flocculation sludge frequencies from 40 to 300 kHz are suitable. Volume reduction of more than 75% has been achieved. The results are used for scaling up the method. This scale-up is subject of a further project, funded by the BMBF, at the Department of Water Quality Control, TU Berlin. (orig.)Available from TIB Hannover: F97B947 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman