The role of compactibility in liquid-solid separation of wastewater sludges

The dewaterability of sludges is generally evaluated by the measurement of specific resistance to filtration (SRF) and capillary suction time (CST). It is generally, but not truly, agreed that the lower figures of these parameters indicate the easiness of sludge dewatering. The biological sludges which have the lower particle size and EPS contents may be characterised as hard-to-filter sludges based on SRF and CST measures. However, cake solids concentration of such a kind of sludge can be unexpectedly higher when the centrifugation is used as the dewatering mechanism. This study introduces compactibility, which is cake solids concentration of sludges after centrifugation as a new measure of dewaterability of hard-to-filter sludges. The results of this study claim that although the filterability indexes (CST and SRF) are moderately high for hard-to-filter sludges, their compactibility might be high indicating particle packing characteristics.