A simple method for evaluating sludge yield stress

Three physical behaviors (liquid, paste-like and solid) can be observed with sludges. The requires laboratory procedures to define the boundary limit between liquid and paste-like behavors (flowability). The yield stress is a typical characteristic of non-Newtonian fluids, in particular for concentrated suspensions, that can be considered as an indicator of sludge flowability. Rotating viscometers are generally used for measuring yield stress, but they are costly and difficult to operate in the field. Therefore, research has been carried out to evaluate this property by adopting simple and applicable field procedures. For experiments two synthetic suspensions of kaolin and quartz sand in water, at different solids concentrations, and an extrusion apparatus (Kasumeter) have been used, and values compared to those obtained by a conventional rotating viscometer. Results showed that the Kasumeter apparatus is able to give yield stress values comparable to those obtained by a rotating viscometer, thus allowing sludge flowability to be evaluated in a very simple way.