Sludge Dewaterability Testing: Relationship Between Capillary Suction Time (CST) and Specific Resistance to Filtration (SRF) for coagulation flocculation sludge

Capillary suction time (CST) and specific resistance to filtration (SRF) are widely accepted measurements to test for sludge dewaterability properties. Previous investigations indicated that CST and SRF are strongly inter-related for most relevant variables. Only few investigations have shown no correlation between CST and SRF. This study aims to assess the goodness of CST and SRF relationship for different process variables relevant for coagulation flocculation sludge. Findings suggested that CST and SRF demonstrate different trends and are not related well for different rapid mixing velocities, materials and temperatures. The lack of overall relationship can be explained by the use of different procedures and equipment at variable boundary conditions in practice. SRF is more temperature-dependent than CST. The use of alum sulphate (alum) and ferric chloride (ferric) resulted in the lowest CST values, followed by Moringa oleifera. This result contradicted the SRF findings for which alum produced the lowest SRF values followed by M. oleifera and ferric.