Mechanical aerators used in wastewater treatment are the largest energy consumers in biological reactors. The main aim of aeration process control in biological reactors for wastewater treatment is to provide the necessary oxygen supply at different working conditions of reactors. The effect of geometric parameters of brush aeration system on the oxygen transfer coefficient (Kla) was studied with the help of experiments carried out in the laboratory. The phenomenon was examined by conducting 150 experiments with brush rotors with five different geometric shapes of blades in which submergence of the blades, distance of the shaft of the rotor from water level and temperature range were varied over fairly wide range. It was found that geometric parameters of brush rotor affect the oxygen transfer coefficient significantly. The maximum value of oxygen transfer coefficient was obtained for blades with angled (triangular) brushes.