Efficacy of Flushing and Chlorination in Removing Microorganisms from a Pilot Drinking Water Distribution System

Abstract

To ensure delivery of microbiologically safe drinking water, the physical integrity of the distribution system is an important control measure. During repair works or an incident the drinking water pipe is open and microbiologically contaminated water or soil may enter. Before taking the pipe back into service it must be cleaned. The efficacy of flushing and shock chlorination was tested using a model pipe-loop system with a natural or cultured biofilm to which a microbial contamination (Escherichia coli, Clostridium perfringens spores and phiX174) was added. On average, flushing removed 1.5–2.7 log microorganisms from the water, but not the biofilm. In addition, sand added to the system was not completely removed. Flushing velocity (0.3 or 1.5 m/s) did not affect the efficacy. Shock chlorination (10 mg/L, 1–24 h) was very effective against E. coli and phiX174, but C. perfringens spores were partly resistant. Chlorination was slightly more effective in pipes with a natural compared to a cultured biofilm. Flushing alone is thus not sufficient after high risk repair works or incidents, and shock chlorination should be considered to remove microorganisms to ensure microbiologically safe drinking water. Prevention via hygienic working procedures, localizing and isolating the contamination source and issuing boil water advisories remain important, especially during confirmed contamination events.

Evaluation of Monochloramine and Free Chlorine Penetration in a Drinking Water Storage Tank Sediment Using Microelectrodes

“…Finally, the importance of regularly cleaning storage tanks and flushing distribution networks should not be underestimated to remove an environment that will protect microbes from disinfectants. The best way to prevent contamination is to have tanks inspected and cleaned regularly, which when combined with effective investigation and flushing maintenance is the key to identifying issues early and responding to adverse conditions promptly to ensure distribution system water quality . The application presented here shows promise and calls for further investigations in laboratory-, pilot-, and full-scale systems.…”

“…The best way to prevent contamination is to have tanks inspected and cleaned regularly, 40 which when combined with effective investigation and flushing maintenance is the key to identifying issues early and responding to adverse conditions promptly to ensure distribution system water quality. 41 The application presented here shows promise and calls for further investigations in laboratory-, pilot-, and full-scale systems. Further studies of the long-term practical effectiveness of monochloramine and free chlorine conversions for controlling microbial activity in drinking water storage tank sediment would be of value.…”

Antibiotic Resistance Patterns of Bacteria Isolated from Dechlorinated Water Samples

“…Excess chloride in water distribution channels may lead to the precipitation of metals in the pipelines [3]. Microorganisms can attach to these precipitated metals and are thus protected from the action of disinfectants [1].…”

“…Disinfection of drinking water supplies is a critical requirement in the provision of safe drinking water [3]. Chlorination is commonly used for the disinfection of water meant for the pipeline distribution network because it is highly effective in destroying pathogens and has residual disinfection effects [4].…”

Climate change and management of biofilms within drinking water distribution systems

“…In operational networks, planned flushing regimes are carried out to manage a clean waterfront through the network, sequentially targeting pipe lengths by closing selected valves and opening hydrants (Ellison, 2003;Vreeburg and Boxall, 2007). Sometimes, flushing can be applied in conjunction with high concentrations of disinfectant (i.e., hyperchlorination) for more effective system cleaning, especially after pipes burst and are repaired (Chaves Simões and Simões, 2013;van Bel et al, 2019). These cleaning methods are known not to completely eliminate biofilm in the networks but remove weaker attached material that is commonly associated with the greatest risk to water quality, including discoloration (Douterelo et al, 2013;Fish, 2013).…”