TABLE OF CONTENTS John L.Cleasby, Ph.D., P.E.
Professor Emeritus
Department of Civil and Construction Engineering
Iowa State University
Ames, Iowa
Gary S.Logsdon, D.Sc., P.E.
Director, Water Process Research
Black and Veatch, Engineers-Architects
Cincinnati, Ohio
The filtration processes discussed in this chapter are used primarily to remove particulate material from water. Filtration is one of the unit processes used in the production of potable water. Particulates removed may be those already present in the source water or those generated during treatment processes. Examples of particulates include clay and silt particles; microorganisms (bacteria, viruses, and protozoan cysts); colloidal and precipitated humic substances and other natural organic particulates from the decay of vegetation; precipitates of aluminum or iron used in coagulation; calcium carbonate and magnesium hydroxide precipitates from lime softening; and iron and manganese precipitates.
A number of different types of filters are used in potable water filtration, and they may be described by various classification schemes. The granular bed and precoat filters discussed herein are comprised of porous granular material. In recent years, interest has grown in the use of membrane filtration in place of, or in addition to, granular bed filtration. Membrane processes are discussed in Chapter 11.
One classification scheme for granular bed filters is based on the type of media used. These filters commonly use a substantial depth of sand or anthracite coal or granular activated carbon or combinations thereof. A typical granular bed filter is shown in Figure 8.1. In contrast, precoat...
