Belt Press Dewatering: Laboratory Simulation of the Pressure Rollers

Belt presses are used for dewatering of flocculent sludge such as polymer conditioned wastewater sludge, industrial sludge, and water treatment silts. This paper describes a portable laboratory apparatus useful for understanding the pressure section of the press. The design of the apparatus is based on pulling a belt pair against a static curved face. Equations for approximating the pressures in full-scale presses as they compare to the static pressure applied with the test units are presented. Results produced by the laboratory equipment at four wastewater treatment plants are compared to full-scale press results. Cake solids produced by the laboratory equipment compared favorably to within 0.4 to 0.6 percent total solids of the cake solids produced at the full-scale plants. In the test apparatus, the sludge cake is not confined at the edges, such that migration of sludge occurs when pressure is applied. Preliminary study of the migration, measured as the increase in cake diameter of one sludge on the laboratory equipment before and after pressing, suggests that migration correlates linearly with initial cake height and compares favorably to full-scale migration measured as the increase in cake width between the wedge and the discharge from final pressure roller.