In the present study, we measured the surface-to-liquid mass transfer coefficient, K-W, for the wall and the immersed vertical cylinder electrodes in the slurry (liquid-solid) and gas-slurry (three-phase) transport beds for controlled solid concentrations in the slurry using the limiting current method. The slurry contained 0.1 min inert glass beads and the solid fraction in the slurry was varied from 0% to 10% by volume. The gas holdup and the solid concentration in the slurry were also measured for the use in correlating the mass transfer coefficients. A unified dimensionless equation with an error of 20.0% in terms of the Sherwood number, the Schmidt number and the specific power group including the energy dissipation rate per unit mass of liquid was obtained for cot-relating the surface-to- liquid mass transfer coefficients in both transport bed systems.