BOOK REVIEW

Solid-Liquid Filtration and Separation TechnologyA. Rushton, A. S. Ward and R. G. HoldichVCH, Weinheim, 1996528 pp, 268DMISBN 3 527 28613 6

Over the past ten years or so several texts on solid-liquidseparation have been published; these have generally falleninto one of three categories. Those books have taken eitheran industrial approach that has often been rather empiricaland pragmatic, or they have been written speci® cally forresearchers, or they have been a presentation of frequentlypublished theoretical analyses of the subject accompaniedby rather simplistic descriptions of the equipment involved.All have their uses, but it is time to marry theories of® ltration to the needs of industrial process design. Attemptsare made by the authors of this book to relate theory topractice in the case of ® ltration equipmentÐ particularlyvacuum and pressure driven equipmentÐ and the practicaluse of the simpler models for equipment sizing and scale-upare given careful consideration by the authors.

The ® rst three chapters of the book describe the principlesof solid-liquid separation, dealing in greater depth with® ltration and sedimentation fundamentals. The treatmentgiven to these topics is comprehensive enough for the readerto be able to use and understand the following chapters andthe theoretical approach adopted puts heavy reliance on thetheoretical developments of Tiller and Shirato. Theseprovide a useful approach to ® lter sizing, but are basedentirely upon empirical constitutive relationships for thesolid-liquid mixture being separated. Partly as a conse-quence, and it must be noted that these chapters do notpretend to bring cake ® ltration theory up-to-date, the readerwill gain little insight of the importance of system chemistryand chemomechanical properties in relation to separationtechnology. However, the Tiller-Shirato model provides theframework for ® lter system design and is used for thispurpose in subsequent chapters. This is done well inChapter 11 for the cases of vacuum and pressure ® lters,and the approach is also used for centrifugal systems inChapter 8; a tentative framework is attempted in a lesssystematic way for micro® ltration (MF) and ultra® ltration(UF) in Chapter 10, but one is left with a false impressionthat the basis, applications and problems of UF are more orless the same as those for MF; the concepts behindclarifying ® lters discussed in Chapter 6 are more diverseand are less easily put into a common framework. Some ofthe calculations are offered in spreadsheet format in theAppendix, which serves to further enhance the link betweenthe theory presented and the simpler process calculationsthat are performed.

Following as authoritative a discussion about ® lter mediaas is possible within a book of this sort, pretreatmenttechniques are given a rather cursory overview. Majoromissions from the latter are the uses and roles of

surfactants, and guidance to the choice and role of¯ occulents. Uncharacteristic of most of the rest of thebook, this chapter is too qualitative and non-speci® c. Adegree of speci® city here about chemical pretreatmentswould have been complementary to other parts of the book.

Chapter 9 is concerned with post-treatment processesÐcake washing and dewatering. The problem of choosingwhich models of cake washing to discuss seems to haveposed a conundrum to the authors, who decided to elaborate(correctly in the view of the reviewer) the dispersion model.However, equations that emanate from other sophisticatedmodels are also presentedÐ yet more advanced cakeformation models are not. The interacting effects of thevarious parts of the ® lter cycleÐ cake formation, washingand dewateringÐ are dif® cult to discover without the readercarrying out a large number of computations. This book hasnot managed to overcome a shortcoming of all others, as itconsiders the ® lter cycle as a series of apparentlyindependent operations, rather than treating the cycle as aprocess that is itself dependent on upstream processes (suchas a reactor of crystallizer) or that affects downstreamprocesses (such as dryers or pelletizers). It would have beeninstructive to see speci® c discussion on and quanti® cation ofthe important linking variables (for example, particle size orcake moisture content). This limiting facet makes theaspects of optimization discussed correspondingly limitedto particular parts of the ® lter cycle, mostly cake formation.

A feature of the book is the breadth of topics it tries topresent, which it does with success. The material has beenused by the authors in short course presentations overseveral years, which has allowed them to gather a number ofpractical problems to illustrate the book. For the discerning,an annoying aspect is the inconsistent presentation format of® gures; within a few pages one ® nds several graphs set inquite different formats with differing typefaces and sizes oflettering, etc.

Notwithstanding some of the comments above, this bookcontains something interesting for everyone concerned with® ltration. For industrial engineers, it forms a most usefulcompilation of information on solid-liquid separationprocesses and provides a considered assessment of thevalue of some of the available calculational procedures. Forthe researcher, the numerous references provide a helpfulstarting point for literature surveys and it gives a goodoverview of established knowledge, although the readermust be aware that the latest theoretical developments arenot always covered by the book. For the student, the bookoffers a wealth of knowledge about the most importantaspects of solid-liquid separation. This is the most usefulcontribution to the ® ltration literature that has appeared formany years in book form, and one that I am sure I will use.

R. J. WakemanUniversity of Loughborough

Trans IChemE, Vol 75, Part A, March 1997

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