Apparatus and method for the dewatering of slimes and sludges. An anode and cathode are provided with the sludge disposed between the electrodes, and with a material for providing a continuation of the boundary layer of the sludge disposed in intimate contact with at least the cathode between the cathode and the sludge, the material allowing the passage of water therethrough, and the cathode being constructed to allow passage of water therethrough. The sludge to be treated is maintained between the electrodes during treatment, and structure is provided to ensure continuous contact between the electrodes and the sludge or the like during treatment even as the volume of the sludge decreases due to water removal. The treatment may be continuous or batch, and by practicing the invention it is possible to render sludge incapable of being dewatered by ambient evaporation so that it is capable of being dewatered by ambient evaporation, while applying only about 200 kwh or less of energy; and it is possible to produce a product sufficiently free of heavy metals to be safely used as a fertilizer from sewage sludge containing significant amounts of heavy metals since the heavy metals pass out of the sludge with the water removed therefrom.