ABSTRACT
The sludges comprise 92–98% moisture, the remaining part being the putrescible organic materials. Subsequent operations, notably those associated with trickling filtration and activated sludge treatment constitute ‘secondary treatment’. Sludge treatment may include all or a combination of the following unit operations and processes: thickening, digestion, conditioning, dewatering, and incineration. The waste liquor from wastewater sludges is often putrescible and high in solids. Sludge thickening and stabilisation are the key processes in water and wastewater treatment facilities practiced before disposal of sludge. The sludge moisture is remove by thickening, conditioning, dewatering, and drying, however, aerobic and anaerobic digestion, incineration, and wet oxidation are used to stabilise the organic material in the sludge. Sludge grinders use one of two techniques: hammer mill pulverizing or cutting. Mechanical mixing may be necessary to assure complete blending of the sludge. Chlorine and hydrogen peroxide are often used to arrest septicity and to control the doors from sludge storage and blend tanks.
