Dewatering of sewage sludges on chamber filter presses

Claim 1

A process for dewatering sewage sludges with a chamber filter press without adding lime, ash or sand wherein the flocculated flake structure of the sludge remains stable in the filter press, which comprises: a. adding an organic flocculant to the sewage sludge in the amount of from 100 to 400 g/m 3 of sewage sludge; b. mixing the organic flocculant with the sewage sludge; c. holding the flocculant and sludge mixture for from 0.5 to 5 minutes for the formation of flocculated sewage sludge particles; d. passing the flocculated sewage sludge to a gravity filtration stage without pumping, thereby preventing the break-up of flocculated sewage sludge particles; e. gravity filtering the flocculated sewage sludge using a gravity filtration means to a sludge solids content of from 10 to 20% by weight; f. passing the gravity filtered flocculated sewage sludge particles to a chamber filter press without using shear forces by conveying using reciprocating diaphragm pumps or eccentric screw pumps, thereby preventing the break-up of the flocculated sewage sludge particles; and then g. pressure filtering the gravity filtered flocculated sewage sludge at a pressure of about 10 to 15 bar using a chamber filter press to a sludge layer thickness of from 15 to 30 mm, the sludge layer thickness being selected to suit the particular sludge to achieve a particularly high dewatered sludge solids content.