Generation of bulk nanobubbles using a high-shear rotor-stator device

We describe the generation of bulk nanobubbles (BNBs)in pure water using a high-shear rotor–stator device. The technique can be used in the batch mode to produce relatively small volumes of BNB suspension on the order of hundreds of milliliters or in the semicontinuous mode to process much larger volumes on the order of tens of liters, making it more amenable for scale-up. The design of the stator influences the effectiveness of nanobubble generation. The two operating modes generate comparable concentrations of BNBs when using similar rotor–stator configurations and hydrodynamic regime. The BNB yield can be enhanced up to a limit through greater energy input, longer operating times, and higher water operating temperatures to release more dissolved air or by continuous additional sparging of air or nitrogen. Sparging CO₂, however, annihilates the generation of BNBs as it forms carbonic acid which is detrimental to the stability of BNBs.