Method of dewatering sewage sludge particularly on recessed plate pressing equipment

Claim 1

A method of dewatering sewage sludge in a filter press including a filter cloth wherein organic polymeric flocculants are added to the sludge to improve the dewatering behavior of the sludge and water is removed from the flocculated sludge in a preparatory stage, comprising the steps of: adding a flocculating amount of an aqueous cationic acrylamide copolymer solution to form a flocculated sludge; maturing the flocculated sludge in a conditioning container for at least two minutes in the absence of mechanical strain prior to feeding it to the filter press, thickening the flocculated sludge in said conditioning container by separating part of the sludge water by decantation using a pump to transport the thickened sludge to the filter press; adding an additional amount of the organic polymeric flocculant to the thickened sludge on the delivery side of the sludge pump to reactivate the flocculated solids agglomerates, wherein the weight ratio of pre-decantation flocculant addition to reactivating flocculant addition is within the range of 3:1 to 9:1; delivering the reactivated solids agglomerates directly to the filter press; and filtering the sludge to provide a filter cake containing at least about 40% dry solids which do not stick to the filter cloth, said aqueous cationic acrylamide polymer solution having been prepared by inverting a water-in-oil emulsion of the polymer, and said aqueous cationic acrylamide polymer solution containing hydrophobic components which hydrophobise the filter cloth during filtering to facilitate filter cake removal therefrom.

Claim 2

A method of dewatering sewage sludge in a filter press including a filter cloth wherein organic polymeric flocculants are added to the sludge to improve the dewatering behavior of the sludge and water is removed from the flocculated sludge in a preparatory stage, comprising the steps of: adding a flocculating amount of an aqueous cationic acrylamide copolymer solution to form a flocculated sludge; maturing the flocculated sludge in a conditioning container for at least two minutes in the absence of mechanical strain prior to feeding it to the filter press, thickening the flocculated sludge in said conditioning container by separating part of the sludge water by decantation using a pump to transport the thickened sludge to the filter press; adding an additional amount of the organic polymeric flocculant to the thickened sludge on the delivery side of the sludge pump to reactivate the flocculated solids agglomerates, wherein the weight ratio of pre-decantation flocculant addition to reactivating flocculant addition is within the range of 3:1 to 9:1; delivering the reactivated solids agglomerates directly to the filter press; and filtering the sludge to provide a filter cake containing at least about 40% dry solids which do not stick to the filter cloth, said aqueous cationic acrylamide polymer solution having been prepared by inverting a water-in-oil emulsion of the polymer, and said aqueous cationic acrylamide polymer solution containing hydrophobic components which hydrophobise the filter cloth during filtering to facilitate filter cake removal therefrom.