TABLE OF CONTENTS Paul J.Delphos
HDR Engineering, Inc.
Norfolk, Virginia
George M.Wesner
Consulting Engineer
San Clemente, California
Coagulation and flocculation may be broadly described as chemical and physical processes that mix coagulating chemicals and flocculation aids with water. The overall purpose is to form particles large enough to be removed by the subsequent settling or filtration processes. Particles in source water that can be removed by coagulation, flocculation, sedimentation, and filtration include colloids, suspended material, bacteria, and other organisms. The size of these particles may vary by several orders of magnitude. Some dissolved material can also be removed through the formation of particles in the coagulation and flocculation processes. The importance of dissolved material removal has become much more critical in recent years with increased regulatory emphasis on disinfection by-products and total organic carbon removal.
There are several excellent discussions on the theory of coagulation and flocculation in Water Quality and Treatment and other AWWA publications listed at the end of this chapter.
Terms used in this chapter are defined as follows:
Coagulation is the process in which chemicals are added to water, causing a reduction of the forces tending to keep particles apart. Particles in source water are in a stable condition. The purpose of coagulation is to destabilize particles and enable them to become attached to other particles so that they may be removed in subsequent processes. Particulates in source waters that contribute to color and turbidity are mainly clays, silts, viruses, bacteria, fulvic and humic acids, minerals...
