The performance of a multi-stage bubble separator was studied with the emphasis on a dimensionless term composed of the backmixing rate between adjacent stages, surface production rate, and two parameters of Langmuir adsorption isotherm. The dimensionless term represents the efficiency of separation in the multi-stage bubble separator, and it can be a scaling-up factor. The number of stages necessary to obtain a given effluent concentration can be obtained by modification of McCabe-Thiel method.