TABLE OF CONTENTS In this chapter the pretreatment of suspensions by chemical and physical means is described from a process engineering perspective. The majority of the text relates to the addition of chemicals that promote coagulation or flocculation, as these are the most widely used and important pretreatment processes. Towards the end of the chapter other methods are discussed; these include the physical pretreatments of heat, freezing and ultrasonics as well as suspension pre-thickening. For the interested reader, aspects of pretreatment processes are discussed in more detail by Akers (1972), Bratby (1980), Glover et al (2004), Gregory (1973), Hermia (1980), Hunter (1995), La Mer and Healy (1966), Kirk-Othmer (1980), Michaels and Bolger (1962), Michaels et al (1967), Moody (1995), Moody and Norman (2005), Purchas and Wakeman (1986), Shaw (1992) and Tchobanoglous and Burton (1991).
Many practical aspects of chemical pretreatments, including extensive descriptions of test equipment and scale-up procedures, are given in Wakeman and Tarleton (2005b).
The throughput and efficiency of solid/liquid separation processes such as sedimentation, filtration and centrifugation are dependent on many interacting variables. They are all primarily affected, however, by the particle size and form of the solids to be separated from suspension. When particle size is small, both gravitational and centrifugal sedimentation rates can be low and filtration often results in the slow formation of high resistance cakes that are subsequently difficult to deliquor and wash. In order to improve the separation characteristics of finer and colloidal suspensions, the primary particle size can be...
