Effect of venturi air hole configuration and aeration duration on oxygen transfer and oxidation kinetics of Fe and Mn in groundwater

Venturi aeration is widely applied in groundwater treatment to enhance dissolved oxygen (DO) levels and facilitate the removal of dissolved metals. Its converging cone creates a pressure drop that increases fluid velocity and generates a vacuum. This vacuum draws in air, forming a two-phase mixture that accelerates oxygen transfer. However, the specific impacts of system geometry and runtime on these kinetics remain poorly understood. This study evaluated the influence of aeration duration and venturi air hole configuration on oxygen transfer efficiency and the oxidation kinetics of iron (Fe) and manganese (Mn). Aeration experiments were conducted for 60 min using venturi injectors equipped with one, two, and three air holes, while DO was measured using both manual methods and an Arduino-based sensor system. The initial DO concentration of 4.9 mg/L increased progressively with aeration time and air hole number, reaching maximum values of 33%, 49%, and 88% for one-, two-, and three-hole configurations, respectively. Correspondingly, Fe concentrations decreased from 0.7182 mg/L to 0.1027, 0.0948, and 0.0088 mg/L, while Mn concentrations declined from 0.3022 mg/L to 0.2287, 0.1551, and 0.0997 mg/L after 60 min of aeration. The venturi aerator configuration with three air holes generated the highest removal efficiencies, namely 98.77% Fe and 67.01% Mn removal. Kinetic analysis showed that the oxidation of both metals followed a zero-order reaction model, with coefficients of determination (R²) of 0.8709–0.9751 for Fe and 0.9078–0.9913 for Mn, and reaction rate constants ranging from 0.0104 to 0.0123 min− 1 for Fe and 0.0012–0.0036 min− 1 for Mn. These results demonstrate that venturi aerator configuration plays a critical role in controlling oxygen transfer and metal removal efficiency in groundwater treatment. The addition of air entrainment holes improves flow characteristics and bubble dispersion that enhances oxygen transfer rate and oxidation kinetics of manganese alongside rapid iron removal without requiring chemical oxidants. Venturi aeration increased dissolved oxygen to 9 mg/L within 60 min. Fe removal efficiency reached 98.77%, while Mn removal achieved 67.01%. Zero-order kinetics dominated Fe and Mn oxidation processes. Turbulence effects on oxygen transfer were assessed.