Escherichia coli Reduction in Water by Zero-Valent Iron–Sand Filtration Is Based on Water Quality Parameters

Improving the microbial quality of agricultural water through filtration can benefit small farms globally. The incorporation of zero-valent iron (ZVI) into sand filters (ZVI–sand) has been effective in reducing E. coli, Listeria spp., and viruses from agricultural water. This study evaluated ZVI–sand filtration in reducing E. coli levels based on influent water type and the percentage of ZVI in sand filters. A ZVI–sand filter (50% ZVI/50% sand) significantly (p < 0.001) reduced E. coli levels in deionized water by more than 1.5 log CFU/mL compared to pond water over six separate trials, indicating that water type impacts E. coli removal. Overall reductions in E. coli in deionized water and pond water were 98.8 ± 1.7% and 63 ± 24.0% (mean ± standard deviation), respectively. Filters constructed from 50% ZVI/50% sand showed slightly more reduction in E. coli in pond water than filters made from a composition of 35% ZVI/65% sand; however, the difference was not statistically significant (p = 0.48). Principal component analysis identified that the turbidity and conductivity of influent water affected E. coli reductions in filtered water in this study. ZVI–sand filtration reduces Escherichia coli levels more effectively in waters that contain low turbidity values.

Parameters for effective sand filtration of Schistosoma mansoni cercariae from water

Schistosomiasis is a water-based neglected tropical disease that is prevalent in over 78 countries. It affects communities that are reliant on freshwater bodies contaminated with schistosome cercariae for their daily water activities. Whilst treatment with the drug praziquantel is relatively effective, it does not prevent reinfection. One option for reducing schistosomiasis infection is providing at-risk communities with treated water, thereby reducing contact with cercaria-infested water for activities such as bathing or doing laundry. This study aims to establish design guidance for sand filtration to remove schistosome cercariae from water. Four sand filters were tested, varying from 300 to 2,000 μm in sand grain size. Each filter was tested with a sand depth of 20 cm, which was increased until no cercariae were detected in the effluent. The required filter depth to remove 100% of cercariae ranged between 40 and 70 cm depending on sand grain size. Cercaria removal was more effective in filters with smaller sand grain size and larger filter depth. These results are valid for intermittent flow, for up to six cycle flushes. While more rigorous testing is needed, these initial results suggest that sand filters can be an effective way to treat cercaria-contaminated water in low-income settings.