An extensive study of changes that occur in waste activated sludge when it is processed by commonly used handling procedures and the effect of these changes on subsequent dewatering of the waste sludge is described. The purpose of the study was to identify the types of conditions that make activated sludge more difficult to dewater and to formulate procedures that would optimize dewatering. The principal handling procedures studied were: anaerobic storage, chlorination, aerobic digestion, polymer conditioning, and combinations of these techniques. The effects of operational parameters on the results were also studied. These include solids concentration, temperature, mixing, dissolved oxygen concentration, aeration rate, and digester flow conditions. Dewatering changes were measured by vacuum filterability, specific resistance, and compressibility. Mechanisms of dewaterability change were elucidated. A procedure for measuring floc size was developed. (Modified author abstract)