AWWA WQTC69247

Coagulation is a process that has been applied in U.S. water treatment practice for over a hundred years. This long history can provide an illusion of familiarity, but changes in goals have altered its application in recent years, suggesting a need for new levels of understanding. Prior to 1989, filtered turbidities of less than 1 NTU were accepted for compliance with regulations. Progressive changes in regulations and greater awareness of the need for more efficient filtration have evolved since this period. Goals for increased levels of performance have emerged, requiring improved control over coagulation since it provides the process mechanisms required for effective removal of particles by granular media filtration. Additional changes in goals have occurred in association with applying coagulation for removal of naturally occurring organic matter (NOM), which reacts with disinfectants to form disinfection byproducts. NOM removal, as measured by changes in total organic carbon (TOC) and UV254, has thereby been proposed as a new focus for coagulation. While goals for this aspect of coagulation are different from those associated with turbidity removal, the set of conditions that must be satisfied can overlap and it is important not to focus entirely on one set of objectives. As such, it is important that an understanding of the coagulation process be advanced in a way that consolidates goals for turbidity and NOM removal as integrated objectives. Includes 4 references, figures.