Effect of Microbubble Mixtures on the Washing Rate of Surfactant Solutions in a Swirling Flow and an Alternating Flow

Wastewater from laundry cleaning contributes to water pollution, and the amount of detergent used needs to be reduced. In the present study, water, four types of surfactants, and their microbubble mixtures were used, and washing rates were measured in swirling flows and alternating flows. The microbubble/water mixtures (average particle diameter: 25 μm; mixed with air at 1.5 vol % in water) achieved washing rates higher than those of water alone. Furthermore, microbubbles mixed with an aqueous surfactant solution had a washing rate that depended on the ionization of the surfactant: the mixtures with microbubbles and non-ionic and anionic surfactants had a washing rate that was higher than that of aqueous non-ionic and anionic surfactant solutions without microbubbles. The surface tensions of microbubble/water mixtures and mixtures of microbubbles with non-ionic and anionic surfactants were lower than those without microbubbles. These results provide evidence of an enhanced washing effect for microbubble mixtures in laundry cleaning.