Effect of Step Geometry and Water Quality on Efficiency of Cascade Aeration

In this paper، the effect of step geometry with five different tread values from 0.40 m to 0.60 m with an increment of 0.05 m and three different types of water namely potable، non-potable and recycled water on aeration efficiency of stepped cascade aeration was studied. detailed experimental investigations were carried out for different hydraulic loading rates of 0.005 m2/s to 0.035 m2/s. all the experiments were conducted for nappe flow condition. results revealed that overall aeration efficiency at standard conditions (e20) approaches maximum for t/h = 4، number of steps = 12، hydraulic loading rate = 0.02 to 0.025 m2/s for potable and non-potable water. in the case of recycled water maximum efficiency was achieved for t/h = 3.67. results also revealed that stepped cascade aeration was found to be a very suitable option for enhancing do content in treatment of waste water before discharging it to water bodies to save aquatic life.