Review of recent trends in Capillary Suction Time (CST) dewaterability testing research

The aim of this review paper is to critically assess recent trends in capillary suction time (CST) dewaterability testing research. The importance of floc structure in explaining practical dewaterability problems such as filter paper clogging is assessed. Current literature on CST for sludge dewaterability is reviewed. The empirical CST test is well-established as the leading method for the determination of sludge dewaterability, despite its shortcomings, such as restricted possibilities to model - and, therefore, predict - physical processes, such as the amount of water bound by the filter 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 is of interest. The use of modified CST tests with a rectangular instead of a circular sludge storage and distribution facility, and a filter paper with smaller pore diameter, were most promising.