The effects of coagulation of organic matter by alum (as influenced by coagulation pH, dosage, and potassium permanganate preoxidation) on the thickening and dewatering characteristics of aluminum hydroxide sludges were examined. Sludge dewatering characteristics worsened as the specific amount of organic matter incorporated into the sludge floc matrix increased. The observed changes in sludge characteristics were correlated to a decrease in sludge floc size and density that occurred when great amounts of organic matter were incorporated into the floc structure. Addition of potassium permanganate improved sludge dewatering rates; the dosage required for improvement was a direct function of the amount of organic matter present in the sludge.
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