ABSTRACT
This chapter describes that only batch studies were conducted by putting about 2 liters of pulp and paper sludge having total solids of about 1.33% in the freezer. The treatment results in a residue called "sludge," which contains a lot of chemicals, especially sulfates and sulfites, in colloidal suspension and dissolved forms, making the sludge less amenable to settling, thickening, conditioning, and dewatering, before final discharge. Many investigators had previously considered natural and indirect freeze-thaw processes on laboratory or large size pilot plant scale experiments as an alternative in conditioning and dewatering of domestic sludges. To overcome or reduce the problems a direct slurry freezing process was developed for conditioning and disposal of the waste activated sludge from sewage treatment works serving residential areas. The improved settling rates, reduction in specific resistance, and the better solids production rate can be attributed to the fact that during the process of slow freezing, the freezing ice exerted a pressure of 12 atm.
