Sludge surfaces and their relation to the rheology of sewage sludge suspensions

An examination of activated, anaerobically digested and aerobically digested sludges has shown that their rheological characteristics are related to the surface charge carried by the component particles. This relation is controlled partly by the ionic strength of the suspending fluid and partly by the chemical nature of the sludge surfaces. Polysaccharides are known to play an important role in determining the surface charge of activated sludge. This study has shown that as the surface polysaccharide content is reduced (by the action of cellulase), so is the viscosity and indicates that surface polysaccharides are significant in determining the viscosity of activated sludge suspensions. The surfaces of other sludge types are not as well characterised and further work than described here is necessary to identify the more significant components for these sludges.