Mechanical dewatering alternatives for waste activated sludge. A pilot study

A pilot investigation of biological sludge thickening and dewatering alternatives, including pressure filtration, precoat vacuum filtration, centrifugation, and ultrafiltration, was conducted on waste activated sludge resulting from the treatment of wastewater from an integrated bleached kraft - fine paper mill. Based upon a criterion of attainable cake consistency, three levels of performance are indicated: (a) pressure filtration and precoat vacuum filtration generating the driest cakes, (b) filter belt pressing yielding intermediate cake consistencies, and (c) gravity filtration, centrifugation, and ultrafiltration resulting in relatively low cake consistencies. In general, performance was found to be severely affected by changes in feed sludge consistency, the amount of sludge conditioning, and the sludge's specific resistance to filtration. The type and amount of sludge conditioning required was shown to be extremely variable, depending upon the dewatering technique employed, the level of performance expected of it, and the consistency and nature of the sludge.