ABSTRACT
This chapter discusses the mechanical and chemical unit operations on sludge that improve substrate availability are referred to as "pretreatment" methods. Sludge handling costs represent 30 to 40% of the capital cost and about 50% of the operating costs of a typical wastewater treatment facility. About two thirds of the volume of sludge in secondary treatment plants is waste activated sludge (WAS). Anaerobic digestion is a commonly used form of secondary sludge stabilization. Digestion of WAS, in which most of the substrate is enclosed within cell membranes, requires conversion of cell bound substrate into more readily accessible forms before it can be utilized by viable anaerobes. While thermal and thermochemical pretreatment of WAS resulted in an increase in biodegradability, these are processes that consume a substantial amount of energy. Any form of low level chemical pretreatment at ambient temperatures, if it increased digestibility, would be desirable.
