Disinfection research in low-income communities (here defined as low-income countries and low-income communities in middle-income countries) around the world has strongly prioritized pathogen inactivation, and rightly so. However, as disinfection becomes widely practiced in low-income communities, chronic health risks from exposure to disinfection byproducts (DBPs) are likely to increase. Factors affecting DBP formation that are specific to low-income settings remain poorly characterized due to a paucity of research as well as over-reliance on trihalomethanes (THMs) as an indicator. The objective of this research is to investigate the impacts of intermittent water supply and point-of-use (POU) disinfection practices on DBP formation through a field study in Dhaka, Bangladesh accompanied by bench-scale experiments. A concern of intermittent supply is that variation in distribution system pressure allows for intrusion of uncontrolled sewage and contaminated stormwater. This problem may be acute in areas such as Dhaka that experience extreme flooding. We conducted sampling campaigns in residential neighborhoods during the dry and rainy seasons. Using artificial sweeteners as a signal of wastewater intrusion, we identified a potential relationship of intrusion with increased formation of nitrogen-containing (N-DBP) classes at the tap. These water systems did not practice centralized disinfection; however, a separate study had installed disinfectant dosers on storage tanks of apartment buildings in the study area. These dosers delivered chlorocyanurates, an alternative chlorine disinfectant popular for POU applications (as well as swimming pools and cleaning products). We measured DBP formation in these systems and conducted bench-scale experiments to compare chlorocyanurates with chlorine bleach. Although chlorocyanurates reduced THM concentrations by ~10-20% relative to bleach in some cases, they promoted the formation of more toxic N-DBPs, Br-DBPs and I-DBPs. The mechanisms of these reactions are further investigated with controlled experiments. These findings have important implications for over 1 billion people served by intermittent water supplies, and for the many communities where centralized disinfection is not reliably practiced. In addition, the results highlight the need for more research on chlorocyanurate chemistry due to their widespread usage and recent implementation by several water systems in the US.

Effects of intermittent water supply and point-of-use disinfection with chlorocyanurates on DBP formation and exposure risk in low-income communities

ACS Fall 2021

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