Mechanism for Enhancing the Ozonation Process of Micro- And Nanobubbles: Bubble Behavior and Interface Reaction

The combination of micro- and nanobubble (MNB) technology with ozonation is a promising wastewater treatment technique that increases the solubility and oxidation capacity of ozone. However, the underlying mechanism remains unclear. We investigated the oxidative capacity of reactive oxygen species (ROS) produced by ozone bubbles of different sizes. Our results show that the process of bubble shrinkage and collapse facilitates the production of ROS. In the domain of MBs with particle sizes ranging from approximately 1 to 100 μm, a reduction in bubble size is positively correlated to increasing tendencies toward bubble shrinkage, collapse, and disappearance. However, ozone NBs have a longer lifespan than MBs, allowing them to collapse continuously and produce ROS over an extended duration of storage time. We studied the specific reaction of ROS production at the gas–liquid interface and confirmed that ozone MNB water produces hydroxyl radicals (•OH) but not hydrogen peroxide (H2O2). •OH is produced by a reaction between ozone and hydroxide ions on the surface of the bubbles. When applied to treating actual reclaimed water, the ozone MNBs shortened the sterilization time of E. coli. The long-term production of •OH by ozone MNBs can be advantageous in water disinfection systems.