Toward One-Step As(III) Removal in Ultrafiltration with In Situ BioMnOx Cake Layer: Mechanism and Feasibility Insights

Abstract

Inorganic arsenic (As) is one of the most significant chemical contaminants in drinking water worldwide. Although membrane-based technologies are commonly used for As removal, they often encounter challenges including complex operation, high energy consumption, and the need for chemical addition. To address these challenges, we proposed a one-step ultrafiltration (UF) process empowered by in situ biogenic manganese oxides (BioMnO_x) cake layers without any additional chemicals, to treat source water contaminated with both As and manganese (Mn). During the filtration, BioMnO_x continuously deposited on the membrane surface with the oxidation of Mn²⁺ by Mn-oxidizing bacteria. The in situ generated BioMnO_x cake layer exhibited a heterogeneous structure, high specific surface area, and significant catalytic activity. Notably, with this BioMnO_x cake layer, the one-step UF successfully achieved a nearly 100% removal of As(III). This high efficiency is due to the catalytic oxidation of As(III) to As(V) by BioMnO_x, followed by the adsorption of As(V) onto the BioMnO_x surface. With the removal of Mn²⁺, new BioMnO_x was continuously formed, which provided new catalytic and adsorption sites, thereby enabling a self-sustained removal of As(III). In addition to the advantages of simple operation and chemical free, the process also exhibited a good economic feasibility with a low energy consumption (0.078 kWh/m³) and a low operating cost (0.229 CNY/m³). Our study provides an example to show that cake layers on membranes are not inherently detrimental and can be beneficial in specific applications.