ABSTRACT
An investigation was conducted to examine conventional disinfection options that would ensure control of Giardia and viruses yet minimize disinfection by-products (DBPs) and conform to disinfectant-disinfection by-product regulations. Primary issues were the types of disinfectants applied (chlorine or chlorine dioxide in combination with chloramines) and their point of application in a large Canadian drinking water treatment plant. Each application point was associated with a different chemical environment that affected disinfectant effectiveness and DBP formation. The effects of implementing different disinfection options on both inorganic and organic DBP formation were evaluated at bench and pilot scale for various raw water conditions. Examination of extremely cold (winter) and high organic content (spring) waters, where ensuring adequate disinfection has typically been difficult, were of special interest. Analyses were conducted for disinfectant residuals, inorganic by-products (chlorite, chlorate), organic by-products (adsorbable organic halides, trihalomethanes, haloacetonitriles, haloketones, haloacetic acids, chloropicrin, and cyanogen chloride), and odors. Promising disinfection strategies were also investigated using a simulated distribution system methodology that allowed the effect of distribution system conditions on DBP formation to be observed. Results have shown that the use of free chlorine as a primary disinfectant followed by chloramination to achieve a calculated overall 4.0 log Giardia reduction (following filtration) would not be compromised by the production of organic DBPs.
