Prediction of reaeration rates in square, stirred tanks
- Indian Inst. of Science, Bangalore (India). Dept. of Civil Engineering
In the biological treatment of wastewaters, aeration is an important process employed to raise the dissolved oxygen (DO) level to allow aerobic bacteria to reduce biochemical oxygen demand of the effluent and thus to improve the water quality. Experiments were conducted on the oxygen transfer coefficient, k{sub L}a{sub 20}, through surface aeration in geometrically similar square tanks, with a rotor of diameter D fitted with six flat blades. An optimal geometric similarity of various linear dimensions, which produced maximum k{sub L}a{sub 20} for any rotational speed of rotor N by an earlier study, was maintained. A simulation equation uniquely correlating k = k{sub L}a{sub 20}({nu}/g{sup 2}){sup 1/3} ({nu} and g are kinematic viscosity of water and gravitational constant, respectively), and a parameter governing the theoretical power per unit volume, X = N{sup 3}D{sup 2}/(g{sup 4/3}{nu}{sup 1/3}), is developed. Such a simulation equation can be used to predict maximum k for any N in any size of such geometrically similar square tanks. An example illustrating the application of results is presented. Also, it has been established that neither the Reynolds criterion nor the Froude criterion is singularly valid to simulate either k or K = k{sub L}a{sub 20}/N, simultaneously in all the sizes of tanks, even though they re geometrically similar. Occurrence of scale effects due to the Reynolds and the Froude laws of similitude on both k and K are also evaluated.
- OSTI ID:
- 323728
- Journal Information:
- Journal of Environmental Engineering, Vol. 125, Issue 3; Other Information: PBD: Mar 1999
- Country of Publication:
- United States
- Language:
- English
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