The present sludge processing operations at the District consist of heated anaerobic digestion, dewatering by centrifugation, and air drying. A critical unit operation in the overall sludge processing train is the mechanical dewatering step. Typically, sludge dewatering by the District's existing centrifuges produces a cake having a solids content of 15%. Four different types of mechanical sludge dewatering machines were evaluated in a pilot test program to determine if these machines could produce cakes having greater solids contents than that produced from the existing centrifuges. The machines tested were two modified versions of the conventional horizontal solid bowl centrifuge design, a screw press, and a diaphragm filter press. The two modified centrifuges produced cakes having average solids contents of 20% and 29.4%, respectively; the screw press produced a cake having an average solids content of 17.5%, and the diaphragm filter press produced a cake having an average solids content of 29.4%. Based on the pilot test program, a test evaluation program was conducted using full-scale centrifuge machines of the modified designs. The preliminary results of this test program confirmed that centrifuges can produce a cake with a solids content approximately equal to or greater than 30%.
A sludge dewatering equipment with a vertical screw press. SOMAPRESS.
