The high compressibility of sludge leads to deterioration of the efficiency of its dewatering process. Therefore the conditioning of sludge before its dewatering is reasonable. This process allows both restsivity and compressibility of sludge to be reduced. It is possible to increase the sludge poros-ity by addition of chemical substances. In the sludge, they can create permeable and stiffer sludge space structure (i.e. grate). The structure developed in this way can be resistant to high

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... e in a mechanical dewatering process. Through the application of ultrasonic field, as a factor that intensifies the action of chemical substances, we pursue boosting of dewatering effects. In this paper, we present the analysis of dewatering effectiveness of a pressure filtration process of sludge after its co-agulation, being conditioned by different methods: only by polyelectrolytes, by ultrasounds + polye-lectrolytes and by chemically neutral substances (ash, gypsum and cement).