Optimization of Sludge Dewatering Through Pretreatment, Equipment Selection, and Testing

Biological sludge dewatering is a crucial step in industrial wastewater treatment processes. There are always challenges as these sludges tend to form highly compressible cakes and the sludge properties are continually changing. In this work, a method was developed to optimize the selection and design of a dewatering process for these highly compressible materials and a case study was used to demonstrate this methodology. A Capillary Suction Time (CST) method was shown to be effective in the initial screening of pretreatment methods. Laboratory pressure filtration can show general trends of the dewatering behavior but cannot match plant-scale operation due to dissimilarities in the equipment configuration and operating procedures. A pilot filter press equipped with both chamber and diaphragm plates was found to work well for this evaluation. It was demonstrated that pressure filtration alone produces wetter cakes (3034wt% cake solids),but with the additional expression exerted by the diaphragm, drier (4144wt% cake solids) cakes can be produced. This work also shows that high sludge-handling capacity can be achieved by shorter cycle times, which can be advantageous, but is offset by the fact that this produces wetter cakes, increasing both the total amount of solids for final disposal and handling cost. The selection and design of a sludge dewatering process needs to include both cake dryness and sludge-handling capacity in the economics analyses to achieve the optimum design.