Freeze-thaw conditioning of sludges: the effect of double layer compression and agitation

Abstract

Freeze-thaw conditioning of sludges is known to be effective and economical when natural freezing is employed. When sludge freezes, both the suspended and dissolved solids are rejected by the growing ice front. The rejected solids are pushed together into tight flocs which are then trapped in the ice. Diffusion drives more water from the flocs to the ice and the particles are forced closer together. Aggegation of particles is achieved, and surface forces keep the particles attached after sludge is thawed. Particles trapped in ice are known to have a very thin layer of water surrounding them. This water does not freeze at normal temperatures. Dissolved solids accumulate in this layer, causing an increase in the ionic strength of the water. This may cause compression of double layer, thus leading to particle aggregation. The first part of the thesis deals with the testing of this hypothesis. Is the hypothesis of double layer compression being a major factor in freeze correct? The second part of the thesis studies the effect of agitation to wastewater sludges after freeze-thaw. /Kir10