Ciba Specialty Chemicals Water Treatments Limited

Janine Marie Griffith

Steven Weir

Simon Paul Oldfield

A method of dewatering a suspension of solids in an aqueous medium, comprising introducing into the suspension a flocculating system, which flocculation system comprises, a) a substantially non-ionic water-soluble polymer and b) a cationic polymeric flocculant of intrinsic viscosity at least 4 dl/g, thereby causing the solids to flocculate, separating the flocculated from aqueous medium, characterized in that i) the components a) and b) are introduced into the suspension as an aqueous blend; or ii) component a) is a non-ionic polymer that has an average molecular weight of below 750,000 and components a) and b) are introduced into the suspension as an aqueous blend or separately. Also claimed is an aqueous composition comprising the substantially non-ionic water-soluble polymer and cationic polymer, method for making it and a composition comprising a blend of substantially anhydrous particles of component (a) and component (b). The method and novel composition are particularly suitable for dewatering aqueous suspensions such as sewage sludges.

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Liversedge, United Kingdom

Janine Marie Griffith