Abstract
.We assessed the ability of sodium dichloroisocyanurate (NaDCC) to provide adequate chlorine residual when used to treat groundwater with variable iron concentration. We randomly selected 654 tube wells from nine subdistricts in central Bangladesh to measure groundwater iron concentration and corresponding residual-free chlorine after treating 10 L of groundwater with a 33-mg-NaDCC tablet. We assessed geographical variations of iron concentration using the Kruskal–Wallis test and examined the relationships between the iron concentrations and chlorine residual by quantile regression. We also assessed whether user-reported iron taste in water and staining of storage vessels can capture the presence of iron greater than 3 mg/L (the World Health Organization threshold). The median iron concentration among measured wells was 0.91 (interquartile range [IQR]: 0.36–2.01) mg/L and free residual chlorine was 1.3 (IQR: 0.6–1.7) mg/L. The groundwater iron content varied even within small geographical regions. The median free residual chlorine decreased by 0.29 mg/L (95% confidence interval: 0.27, 0.33, P < 0.001) for every 1 mg/L increase in iron concentration. Owner-reported iron staining of the storage vessel had a sensitivity of 92%, specificity of 75%, positive predictive value of 41%, and negative predictive value of 98% for detecting > 3 mg/L iron in water. Similar findings were observed for user-reported iron taste in water. Our findings reconfirm that chlorination of groundwater that contains iron may result in low-level or no residual. User reports of no iron taste or no staining of storage containers can be used to identify low-iron tube wells suitable for chlorination. Furthermore, research is needed to develop a color-graded visual scale for iron staining that corresponds to different iron concentrations in water.
Highlights
Household chlorination is one of the most cost-effective point-of-use (POU) water treatment interventions in resourcelimited settings.[1]
Our objectives were to assess whether 1) small-scale geographic variation of iron concentration may exist in these relatively low groundwater iron areas, 2) NaDCC tablets provide the recommended chlorine residual when used to chlorinate groundwater with varying iron concentration, and 3) user-reported iron taste and iron staining on storage containers are accurate proxy indicators of high groundwater iron concentration
Median iron concentration of tube wells varied within small geographical areas with significant variation between villages in the same union (P = 0.008) and between unions (P = 0.0001)
Summary
Household chlorination is one of the most cost-effective point-of-use (POU) water treatment interventions in resourcelimited settings.[1]. Groundwater is used for drinking purposes in many countries and often contains reduced forms of iron, arsenic, manganese, and sulfur. These reduced chemicals react with chlorine-based disinfectants and increase the chlorine demand.[6] The effectiveness of chlorine-based disinfectants in providing the targeted levels of residual-free chlorine in treated groundwater varies with the chemical makeup of the groundwater aquifer.[7] Efforts to use chlorine-based disinfectants such as calcium hypochlorite and sodium hypochlorite to treat groundwater were unsuccessful in Bangladesh,[8,9] likely because of the interference with groundwater chemicals
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