AWWA WQTC62542

For the AWWARF funded project "Long Term Effects of Disinfection Changes on Water Quality", a number of utilities completed surveys and provided information describing the changes that they have made to their disinfection schemes and what they have discovered about the water quality within the distribution system. The study encompasses utilities that have made the following changes: chlorine to ozone for primary disinfection for both filtered and unfiltered water systems; chlorine to chlorine dioxide for primary and secondary disinfection; chlorine to ultraviolet light irradiation for primary or secondary disinfection; and, chlorine to chloramines for secondary (distribution system) disinfection for both filtered and unfiltered water systems. Each case study presents background about the utility, factors driving the decision for disinfection change, water quality before and after the disinfectant change with regard to microbial quality, disinfection byproducts, water chemistry and customer complaint records. The case studies highlight each type of the major disinfection change. The purpose of the study is to document changes in Distribution System Water Quality in all of the major areas that affect public health and acceptance of the water. The foremost reason to disinfect water is to improve the microbiological quality of the water. While chlorine has performed this task admirably for at least a century, the discovery of undesirable chemical reactions between chlorine and organic matter and the emergence of chlorine resistant pathogens such as Giardia lamblia and Cryptosporidium as waterborne pathogens has driven the search for new disinfection schemes. Issue papers prepared as one of the preliminary steps in the this project described theoretical or previously documented effects of a change from chlorine to chloramines, ozone, chlorine dioxide, or ultraviolet light on water quality. The issue papers addressed key factors affecting water quality changes, positive impacts on water quality, potential adverse impacts on water quality, and information gaps and data needed to fill those gaps. The case studies below focus on successful changes in disinfection scheme to present models and provide guidance to other utilities contemplating changes to their disinfection schemes. Includes table, figures.