(Received December 4, 2007; accepted April 9, 2008; published online August 8, 2008)
Recently, technology using microbubbles has been studied for water purification. However, the mechanism and physical parameters of the purification process have not yet been sufficiently clarified. The purpose of this study is to clarify the physical parameters of microbubbles that influence water purification. Firstly, we measured and analyzed the purifying performance using various millimeter-sized bubbles, and we obtained the equilibrium constant of the pollutant adsorbed on the bubble surface from the experimental results. Secondly, we experimented with purifying the polluted water using microbubbles and clarified that the purification performance of microbubbles agreed with that theoretically expected using the equilibrium constant obtained in the preparatory experiment. We assume that an important parameter affecting adsorption on the surface of microbubbles is the equilibrium constant in the chemical potential. Because the equilibrium constant is derived from the surface chemical potential, it is equal to the bulk chemical potential of the liquid. In the microbubbles diameter (70 µm) range in this study, we have found that the most significant factor determining the adsorption is the surface area. The surface tension of microbubbles is not significant factor.
KEYWORDS:microbubbles, purification, adsorption coefficient, oleic acid, chemical potential