BACKGROUNDIn comparison with ordinary bubbles, microbubbles exhibit low floating rate and high surface charge density. More importantly, microbubbles shrink gradually and the gas-liquid interface charges congest significantly, generating large surface potential and energy, which promotes the formation of reactive oxygen species (ROS) when microbubbles eventually collapse. In this study, size-controllable microbubbles were introduced to alkaline solutions by titanium microporous filters, and the effects of microbubble diameter, alkaline concentration and temperature on the formation of ROS were examined.