AWWA ACE68637

The goals of this powerpoint presentation were to: assess the impact of dynamic water quality conditions on microorganism inactivation; identify the factors that affect the maintenance of a secondary disinfectant residual, including the benefits of maintaining various target levels; determine the ability of a disinfectant residual entering the distribution system to inactivate microorganisms that may be encountered; and, assess the ability of a disinfectant residual to serve as an indicator for distribution system microbial integrity. "Impact of Distribution System Water Quality on Disinfection Efficacy" (AwwaRF / USEPA Project 2771) includes the following four phases: revisit existing information in the form of a literature review, a modeling effort, utility survey and historical water quality data analysis; determine inactivation potential (bench scale); evaluate the impact of acute and chronic water quality changes on disinfection efficacy; and, examine analytical limitations of secondary disinfectants (organochloramines). The goal of annular reactor testing is to assess efficacy of free chlorine and monochloramine to inactivate suspended and attached microorganisms. The objectives of annular reactor testing are to: determine target disinfectant residual to preserve water quality during simulated microbial contamination; evaluate the impact of pipe material and water age on water quality, disinfection efficacy and biofilm production; and, examine the usefulness of flushing and increased disinfection to remediate microbial contaminations. The experimental plan is presented, along with the results of the disinfection phases and pulse of E. coli. Presentation summary includes the following: Acclimation phase -- the upstream reactor of each train had the highest biofilm HPCs, followed by the middle reactor, and then the downstream reactor; Low-level disinfection phase -- biofilm HPCs did not increase in the upstream reactors (disinfectant residual), but increased in the downstream reactors; High-level disinfection phase -- suspended HPCs at train effluent were lower; little effect on biofilm HPCs (increase when compared with acclimation phase); log reduction of suspended and biofilm HPCs was higher in the chlorinated trains than in the chloraminated trains with comparable Ct values; monochloramine was more efficient than free chlorine against biofilm coliforms, but less efficient than free chlorine against suspended coliforms in the CI reactors; and, biochemical assays indicated that coliforms isolated from the bulk liquid differed from those isolated from the biofilm of the same reactor. Includes figures.