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 by 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 m(2)/s to 0.035 m(2)/s. All the experiments were conducted for nappe flow condition. Results revealed that the overall aeration efficiency at standard conditions (E-20) approaches the maximum for t/h = 4, number of steps were 12 with a hydraulic loading rate of 0.02 to 0.025 m(2)/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 a very suitable option for enhancing DO content in treatment of waste water before discharging it to water bodies to save aquatic life. (C) 2016 Sharif University of Technology. All rights reserved.