Mass-transfer studies were carried out to characterize a porous, RVC, flow-by mode, single-pass reactor for the application of removing heavy metals from waste waters. Measurements of the limiting current and concentration for the reduction of the ferricyanide ion and copper ion respectively, show that the average mass-transfer coefficients were proportional to Re-0.7. The current was also monitored over extended periods of copper ion deposition to describe the plugging of the porous electrode.