The shear sensitivity of activated sludge - Relations to filterability, rheology and surface chemistry

Many solid/liquid separation properties are dependent upon the number of li ne (micron sized) particles present in the suspension, which in turn is a c onsequence of the flocculation/break-up balance of the sludge. The present study revealed strong correlations between the dispersed mass concentration , resistance to filtering (capillary suction time) and rheological paramete rs for activated sludge suspensions of varying solids content. It seems lik ely that the restriction of flow caused by development of inter-particle ne tworks causes increased surface erosion of primary particles. The increased dispersed mass concentration in turn causes deterioration of filterability . The shear sensitivity parameter quantifies the degree of dispersion in re sponse to turbulent shear and is thus expected to be of prime importance fo r solid/liquid separation processes. The parameter reflects changes of the surface chemistry, and is therefore suitable as a means of assessing variat ions of surface chemistry for full scale activated sludge plants. Differenc es in interaction energies of different sludges may be estimated from shear sensitivity estimates. The observed changes in interaction energy upon add ition of sulphide or detergent, changed pH or lowering of the ionic strengt h were in qualitatively agreement with DLVO-theory. (C) 2001 Elsevier Scien ce B.V. All rights reserved.