Intensified ozonation in packed bubble columns for water treatment: Focus on mass transfer and humic acids removal

Ozonation has been widely applied for the oxidation of contaminants in wastewater, and the disinfection of water. However, low ozone (O₃) mass transfer efficiency in common ozonation reactors requires high O₃ doses and causes high energy consumption. In this study, to intensify the O₃ mass transfer and oxidation of humic acids (HA) solution, a lava rock packed bubble column (LBC) and a metal pall ring packed bubble column (MBC) were developed and evaluated. In comparison with non-packed bubble column (BC), both LBC and MBC enhanced the O₃ mass transfer efficiency and the generation of hydroxyl radicals, thereby increasing the HA removal from an aqueous solution. At applied O₃ dose of 33.3 mg/(L_column h), the HA removal efficiency in BC was only 47%. When MBC and LBC were applied, it increased to 66% and 72%, respectively. Meanwhile, the O₃ utilization efficiency in LBC reached 68%, which was higher than that in MBC (50%) and BC (21%). Consequently, LBC has the lowest energy consumption (E_EO) for HA removal (1.4 kWh/m³), followed by MBC (1.6 kWh/m³) and BC (2.9 kWh/m³). LBC had better performance than MBC due to the adsorptive and catalytic roles of lava rock on the ozonation process. This study demonstrates the advantages of using lava rocks as packed materials in O₃ bubble column over metal pall rings in intensifying O₃ mass transfer and organic matters removal, which provides some insights into promoting the industrial application of O₃.