Dewatering Sludges Using a Novel Membrane Technology

Abstract

A novel tubular configured filter press has been developed for the filtration or dewatering of sludges. The unique features of this filter press are:during the cake deposition stage, sludge is fed under pressure into a self-supporting array of horizontal collapsible porous fabric tubes (the cake is deposited on the internal walls of the tubes).during the cake removal stage, sludge is pumped through the array of tubes at a high velocity and the cake is dislodged from the tube walls by means of a roller cleaning device which traverses the length of the array of porous tubes. The dislodged cake, which is in the form of flakes, is simultaneously hydraulically transported out of the tubes, drained and conveyed to a collection hopper. A brief process description of the tubular filter press process is given. A prototype unit was erected at a water treatment plant to dewater clarifier waste sludge. The cake produced by the filtration of the clarifier waste sludge was very compressible. After tube blockage problems were experienced during the filtration cycle on the prototype unit, research was done on the deposition of a compressible cake inside a porous tube. A predictive internal cylindrical compressible cake filtration model was developed. The results of this research work are discussed. The differences between internal cylindrical, external cylindrical and planar compressible cake filtration are highlighted. At various times low cake recoveries (high cake losses) were experienced on the prototype unit. An investigation was consequently conducted into the dislodging of a very compressible cake during the cake removal process. The results of this investigation are discussed.