New insights into the role of powdered activated carbon in Mn(II) oxidation by ozone

Ozone–activated carbon (O 3 /AC) systems are widely applied for the removal of soluble manganese (Mn(II)) in drinking water treatment. However, the underlying mechanisms remain poorly understood. In this study, the effects of granular activated carbon (GAC) and powdered activated carbon (PAC) on Mn(II) removal by O 3 were investigated. Mn(II) was rapidly removed by O 3 alone ( k obs = 0.069 s −1 ), whereas lower rate constants of 0.048 and 0.031 s −1 were observed in the O 3 /GAC and O 3 /PAC systems, respectively, at pH 7.0. Although increasing pH enhanced Mn(II) oxidation by O 3 alone, the inhibitory effect of PAC became progressively stronger from pH 7 to 9. The inhibitory effects of GAC and PAC on Mn(II) removal were closely associated with enhanced O 3 consumption, as demonstrated by O 3 decay experiments. Although hydroxyl radicals (•OH) and superoxide radicals (O 2 •⁻ ) were generated in the O 3 /GAC and O 3 /PAC systems, radical scavenging experiments demonstrated that these species contributed negligibly to Mn(II) oxidation. Overall, GAC and PAC enhanced O 3 consumption and reduced Mn(II) removal. These findings provide new mechanistic insights into the role of AC (especially PAC) in O 3 oxidation for Mn(II) removal and contribute to a deeper understanding of combined O 3 /AC oxidation processes.