Review of Capillary Suction Time Testing

M. Scholz, O. Sawalha, and D. Borges (UK)


Sludge dewaterability testing, capillary suction time (CST), funnel geometry, filter paper, solids, and floc structure


The aim of this review paper is to critically assess recent trends in capillary suction time (CST) dewaterability testing research and application. The importance of floc structure in explaining practical dewaterability problems such as paper clogging is highlighted. The empirical CST test is well established as the leading method for the determination of sludge dewaterability despite its shortcoming of restricted modeling possibilities, and therefore limited predictability of the physical processes such as the amount of water bound by the paper. Nevertheless, the CST apparatus is portable, and the method is easy to conduct, quick, cost-effective and accurate, if the product of solid concentration and average specific resistance to filtration are of interest. Modified CST tests with a rectangular instead of a circular sludge storage and distribution facility, as well as a (filter) paper with a relative small pore diameter were promising.

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