TABLE OF CONTENTS Raymond D.Letterman, Ph.D., P.E.
Professor, Department of Civil and Environmental Engineering, Syracuse University, Syracuse, New York
Appiah Amirtharajah, Ph.D., P.E.
Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia
Charles R.O Melia, Ph.D., P.E.
Abel Wolman Professor, Department of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, Maryland
Coagulation is a process for increasing the tendency of small particles in an aqueous suspension to attach to one another and to attach to surfaces such as the grains in a filter bed. It is also used to effect the removal of certain soluble materials by adsorption or precipitation. The coagulation process typically includes promoting the interaction of particles to form larger aggregates. It is an essential component of conventional water treatment systems in which the processes of coagulation, sedimentation, filtration, and disinfection are combined to clarify the water and remove and inactivate microbiological contaminants such as viruses, bacteria, and the cysts and oocysts of pathogenic protozoa. Although the removal of microbiological contaminants continues to be an important reason for using coagulation, a newer objective, the removal of natural organic material (NOM) to reduce the formation of disinfection by-products, is growing in importance.
Aluminum and ferric iron salts have long been used to remove color caused by NOM. These organic substances are present in all surface waters and in many groundwaters. They can be leached from soil, diffused from wetland sediments, and released by plankton and bacteria. Natural organic material adsorbs on natural particles and acts as...
