MnO₂-modified activated carbon and granular nano-TiO₂ in tandem succeed in treating domestic well water arsenic at point of use

Globally, millions of rural households that use groundwater for drinking are exposed to inorganic arsenic, frequently as arsenite (As(III)). Crucial for health protection, adsorption-based treatment works well for arsenate (As(V)) but not for slower-adsorbing As(III). Liquid oxidants, though impractical for point of use, are widely used to pre-oxidize As(III) to As(V) in point-of-entry treatment for better performance and cost saving. Here MnO₂-modified activated carbon, a solid oxidant, was integrated into a point-of-use system with granular nano-TiO₂ as the main adsorbent for two real-world tests, supplying As-safe water at less than US$0.01 l⁻¹. One 4-month deployment treated 4,200 bed volumes (~2.1 m³) of groundwater with 69 ± 16 μg l⁻¹ As (78 ± 5% As(III)). Another 28-month deployment treated 10,000 bed volumes (~5.0 m³) of groundwater with 42 ± 21 μg l⁻¹ As (33 ± 21% As(III)). Interactions between the groundwater matrix and filter media affect performance, highlighting the need to verify household As removal technologies through long-term deployments.