Air-water flow and gas transfer at aeration cascades: A comparative study of smooth and stepped chutes

While stepped spillways are common design for energy dissipation purposes, aeration cascades are used for in-stream re-aeration, in water treatment plants to enhance the air-water transfer of atmospheric gases (e.g. oxygen, nitrogen) and for the removal of volatile organic components (VOC) such as methane and chlorine. The present study present new detailed characteristics of the air-water flows and interfacial properties. New experiments were performed in a large stepped cascade (35-m long, 0.5-m wide) to minimise scale effects. A comparative analysis of air-water gas transfer rate is developed between smooth-invert and stepped chute. The results demonstrates that the aeration cascade is at least 10 times more efficient than the corresponding smooth chute.