Patent ID: 7754087

Claim:
A process of dewatering an aqueous sewage sludge suspension employing a flocculating system comprising i.) treating the suspension with a flocculating amount of a first flocculant having a molecular weight of at least one million and a dewatering amount of a second flocculant, which second flocculant is in the form of particulates, ii.) thickening the treated suspension of step i.) by release of free water, iii.) mixing the thickened suspension, wherein the second flocculant particulates are distributed throughout the thickened suspension of step ii.), using mixing equipment, and iv.) subjecting the suspension to mechanical compression dewatering to form a cake, wherein the first flocculant brings about flocculation and assists thickening of the suspension and the second flocculant further dewaters the suspension, characterised in that the second flocculant is a water-soluble or water swellable polymer formed from 80 to 100% by weight methyl chloride quaternary ammonium salt of dimethyl amino ethyl (meth)acrylate and 0 to 20% by weight acrylamide of intrinsic viscosity between 3 and 10 dl/g that is mixed into the suspension in the form of a water-soluble or water swellable particulate polymer having a particle diameter of at least 50 microns, wherein the first and second flocculants are not counterionic and the first flocculant is cationic acrylamide polymer.