Filter press is an applicable dewatering technique primarily for sludge. It offers advantages for difficult sludge because it is a batch operation where the sludge can be kept under pressure on the filter for extended periods of time until it dewaters to desired consistency. Filtrate liquors produced are usually low in suspended solids content.
Filter press consists of number of plates that are held rigidly in a frame to ensure alignment and are pressed together hydraulically, between a fixed and a moving end. It is a fixed volume recessed plate filter press type, or also called chamber filter press. Liquid is pumped by high-pressure pumps into a volume between two filter plates. On the face of each individual plate, a filter cloth is mounted. As a result of the high pressure that the sludge is under in, a substantial portion of the water in the feed sludge passes through the filter cloth and drains from the press. Sludge solids and the remaining water eventually fill the void volume between the filter clothes, so that continued pumping of solids to the press is no longer productive. At this point, pumping is stopped and the press is opened to release the dewatered sludge cake prior to initiation of new “pressing cycle”. Filter press is installed well above floor level so that the cake can drop out into hoppers positioned underneath the press, where it is to be disposed by truck.