Arsenic is known as a toxic element to humans, and has been reported to co-exist with iron and manganese in groundwater worldwide. The typical method for arsenic removal from groundwater is to oxidize trivalent (As(III)) to pentavalent (As(V)) followed by the As(V) removal. This study aims to evaluate the oxidization efficiency of As(III) in a mature biological manganese (Mn²⁺) removal filtration system with different elevated influent As(III) concentrations. The effects of influent Mn²⁺ concentrations, influent As(III) concentrations, filtration rates and dissolved oxygen (DO) levels on the efficiency of As(III) oxidation were assessed. The results showed that As(III) oxidation can be simultaneously achieved with removing Mn²⁺ in the filtration system. The oxidation efficiency was not impacted by increasing the influent As(III) concentration up to nearly 2500 µg L⁻¹, but the filtration rate was limited at 11 m h⁻¹ for maintaining the effluent As(III) concentration below 10 µg L⁻¹. The oxidation process followed first-order kinetics with the constant reaching 0.56–0.61 min⁻¹. The As(III) oxidation process was most likely to be mediated by the bacterial community initially developed for Mn²⁺ removal in the filtration system, which performed the catalytic oxidation for As(III).

GRAPHICAL ABSTRACT