For the AWWARF funded project "Long Term Effects of Disinfection Changes on WaterQuality", a number of utilities completed surveys and provided information describingthe changes that they have made to their disinfection schemes and what they havediscovered about the water quality within the distribution system. The study encompassesutilities that have made the following changes:chlorine to ozone for primary disinfection for both filtered and unfiltered watersystems;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 bothfiltered and unfiltered water systems.Each case study presents background about the utility, factors driving the decision fordisinfection change, water quality before and after the disinfectant change with regard tomicrobial quality, disinfection byproducts, water chemistry and customer complaintrecords. 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 inall of the major areas that affect public health and acceptance of the water. The foremostreason to disinfect water is to improve the microbiological quality of the water. Whilechlorine has performed this task admirably for at least a century, the discovery ofundesirable chemical reactions between chlorine and organic matter and the emergenceof chlorine resistant pathogens such as Giardia lamblia and Cryptosporidium aswaterborne pathogens has driven the search for new disinfection schemes.Issue papers prepared as one of the preliminary steps in the this project describedtheoretical or previously documented effects of a change from chlorine tochloramines,ozone,chlorine dioxide, orultraviolet lighton water quality. The issue papers addressed key factors affecting water quality changes,positive impacts on water quality, potential adverse impacts on water quality, andinformation gaps and data needed to fill those gaps. The case studies below focus onsuccessful changes in disinfection scheme to present models and provide guidance toother utilities contemplating changes to their disinfection schemes. Includes table, figures.
