Digested Sludge Thickening Experiences in Yorkshire Water's Southern Division

S ludge T reatment and disposal costs contribute a large proportion to the overall operating costs of sewage treatment installations. With the increasing drive towards more cost-effective operation it has been recognized that thickening sludge prior to disposal can achieve significant cost savings for limited capital outlay. This paper describes the practical experiences at the Lundwood, Old Whittington, and Aldwarke works of Yorkshire Water (YW) where digested sludge is gravity thickened in shallow tanks of large surface area prior to land disposal. Existing structures have been utilized where possible to minimize capital cost. Digestion plant operational data for the three works are given, and an evaluation is made of cost savings resulting from the post-digestion thickening process.