Dewatering and drying of wastewater treatment sludge

Sludge is the name that describes a muddy or slushy mass, deposit, or sediment as (1) the precipitated solid matter produced by water and sewage treatment processes; (2) mud from a drill hole in boring; (3) the muddy sediment in a steam boiler; (4) waste from a coal washery; or (5) the precipitated or settled matter from industrial processes. Water treatment sludge consists of suspended solids, coagulation chemicals, usually an alum or polymers with a limited amount of biological materials. A comprehensive review of industrial sludge can be found elsewhere [1]. In that review, sludge from petroleum, metal-nishing, flue gas cleaning, water treatment, pulp and paper processing, polymer plants, chemical plants, as well as mineral and metallurgical industries are discussed. The sludge addressed in this chapter is the by-product of a wastewater treatment plant. Brief reviews on the treatment, usage, and disposal of this type of sludge are available [2,3]. In this chapter, we take a comprehensive approach to examine the literature on sludge dewatering and drying in order to give readers a relatively detailed and complete picture of this area that is growing with the expenditures on environmental cleanup and control, amounting to about US $150 billion in the United States and about US $400 billion globally in 1997 [4].