Role of manganese oxides for enhanced the removal of dissolved manganese by aeration process using pilot-scale bubble column: Key role autocatalysis, kinetic modeling, performance comparison, and economic evaluation

Dissolved manganese (Mn(II)) removal from drinking water by an aeration-based oxidation process was investigated in a pilot-scale bubble column reactor (BC) reactor. The study examined the effects of pH, aeration flow rate, and in-situ formed MnO2 on Mn(II) oxidation efficiency. Experimental results showed that Mn(II) removal was not limited by oxygen mass transfer. Raising the pH from 9.2 to 10 and increasing Mn(II) concentration significantly enhanced oxidation efficiency, reducing the time for 90 % removal from 119 min at pH 9.5-25 min at pH 10. Furthermore, Mn(II) oxidation kinetics exhibited strong pH dependency and autocatalytic behavior, as confirmed by a kinetic model fitting well with experimental data. XRD, FTIR, SEM, and PSD analyses highlighted the formation of mixed Mn(III) and Mn(IV) oxides with varying sizes and morphologies, influenced by pH. Compared to the BC reactor, the ALR achieved 90 % Mn(II) removal in just 25 min with 0.029 kWh.m-3, whereas the BC required 60 min and 0.072 kWh.m-3. This was attributed to the ALR's superior internal mixing, ensuring homogeneous pH and MnO2 dispersion. Additionally, physicochemical analyses revealed that increasing pH from 9.2 to 10 altered the crystallographic structure, shape, and size of manganese oxides. These findings highlight the potential of optimizing aeration-based oxidation for Mn(II) removal, emphasizing the role of operating conditions, reaction mechanisms, and energy efficiency in enhancing process performance.