Integrated disinfection strategies for treatment of drinking water

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In drinking water distribution systems, bacteria and other pathogens tend to cluster on pipe surfaces, otherwise known as the formation of biofilm. Disinfection is a key step for minimizing this formation, which has the potential to lead to an increase in pathogenic microorganisms. Suppliers will often utilize primary and secondary disinfectants in combination in the treatment process for different reasons, and although this is a widely used practice little emphasis has been placed on the potential for synergistic benefits between disinfectants. Synergistic benefits would include an enhanced ability to reduce bacteria in distribution systems when the disinfectants "work together". There have been few studies published that were designed specifically to investigate synergy, especially using UV light for the treatment of drinking water. Previous work done by Dr. Rand has established in laboratory tests that synergy exits between UV light and chlorine-based disinfectants for removing Escherichia coli (E. coli). It was also found in field studies through simulating distribution systems that there was potential for synergistic benefits. To calculate synergy, a concept presented by Koivunen et al. (2005) was adopted, which stated that synergy was present when the removal of a combined disinfection strategy was greater than the sum of removals achieved by each disinfectant alone. Although this is a useful equation, it relies on disinfectant efficacy alone. Therefore, it is difficult to apply in long-term studies, where pipe material, water quality, nutrient supply and other issues would play a serious role in the formation of biofilm. However, if synergy could be quantified realistically, this could lead to suppliers being able to reduce more pathogenic microorganisms without increasing disinfectant dosages. The purpose of this research is to investigate the potential for synergy between disinfectants under different conditions and to develop a model to quantify synergy so that utilities might be able to simulate their systems without long-term bench and pilot studies.