Consolidation theory applied to the Capillary Suction Time (cst) apparatus

The Capillary Suction Time-method was introduced in 1967, and was designed for establishing the dewaterability of sludge samples. The CST-test was developed as an alternative to the more cumbersome filtration tests using vacuum pumps. Over the years, extensive research has been conducted on models describing the dewatering process in this apparatus. Most of these models have been based on traditional filtration theory, comprising an assumed average cake filtration resistance. An alternative theory which has not been investigated in this respect before is the large-strain consolidation model proposed by Gibson (1967). When this particular consolidation theory is applied to the CST-apparatus, it can be shown that from measurements with the CST-test, conducted on a series of samples of a certain sludge or soil with different initial void ratios (or water contents), the coefficient of consolidation of the soil can be deduced. The benefits of this approach are multifold. BY describing the dewatering of a sludge with the consolidation theory, e.g. in a lagoon, filter press, centrifugal pumps and so forth, the dry matter content can be predicted with respect to time using the coefficient of consolidation found with the CST-test. Also, the influence of polyelectrolytes added to the sludge to improve the dewaterability can be measured quantitatively as an increase of the coefficient of consolidation. (C) 1998 IAWQ. Published by Elsevier Science Ltd.