The characterisation of slurry dewatering

The dewatering of flocculated suspensions presents a significant challenge to water and waste water processing operations world-wide. Traditionally the dewatering process is enhanced through the use of flocculants or a surface chemical modifier to draw together fine particles and increase settling rates and sediment permeabilities, however, present methods of gauging chemical performance are somewhat empirical. Recently, Landman and White developed a theory of suspension filtration which incorporates the compressibility and permeability of a sediment into a filtration diffusivity, D(φ). D(φ) is a material property used to calculate the time scale of a dewatering process from first principles for a given set of process conditions i.e. final desired solids concentration, applied pressure, initial sediment height. A model alumina system and an alum water treatment sludge have been used to show the effect of flocculation conditions on compressibility, permeability (determined from filtration experiments) and the diffusivity, D(φ).