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Title:Effects of oxygen demand on surface reaeration
Author(s):Holley, E.R.; Sollo, F.W.
Contributor(s):Pazwash, Hormoz; University of Illinois at Urbana-Champaign; Illinois State Water Survey
Subject(s):Water resource development--Illinois
Water resource development
Water quality
Dissolved oxygen
Oxygen demand
Water pollution
Geographic Coverage:Illinois (state)
Abstract:An extensive literature review is presented pointing out that the transport or diffusion of dissolved oxygen in the thin region or film immediately below the water surface is the most critical region in determining the oxygen absorption rate. Literature on the effects of sodium sulfite and biochemical oxygen demand (BOD) is also reviewed. The surface film is actually an oxygen boundary layer. This concept is supported by the definition of a boundary layer, by reaeration experiments, and by analogy with other mass and heat transfer problems. Thus, it should be expected that the film or boundary layer thickness changes with Schmidt number as well as mixing conditions and that the transport through the film can be represented by a diffusion model., as in other boundary layer problems. Temperature measurements were made to allow the calculation of the diffusion coefficient in the thermal boundary layer or film in a situation analogous to the reaeration problem. The results indicate that the diffusion coefficient is approximately equal to the molecular diffusivity even when turbulence is present. Using the boundary layer and diffusion model, analytical solutions are presented for the vertical concentration distribution both in the turbulent film and below the film for various situations involving no oxygen demand, sulfite, or BOD. The solutions substantiate that the concentration distribution is essentially linear in the film even in the unsteady absorption problem both with no oxygen demand and with BOD. The degree of approximation involved in making certain simplifying assumptions is demonstrated. The solutions show that the oxygen demand per se of the BOD does not affect the absorption rate, but the possibility is left open for other effects, such as physical influences, to affect the absorption rate. The solutions for the effects of sulfite in increasing the absorption rate are in general agreement with available data. Experiments were performed at 2°C and at 20°C to evaluate the effects of BOD on reaeration rates. For both temperatures, the reaeration rates were about 1.5 times the rate for pure water. Since biological activity is almost non-existent at 2°C, the increase must have been due to the physical presence of the organisms.
Issue Date:1970-09
Publisher:University of Illinois at Urbana-Champaign. Water Resources Center
Genre:Report (Grant or Annual)
Sponsor:U.S. Department of the Interior
U.S. Geological Survey
Rights Information:Copyright 1970 held by E.R. Holley, F.W. Sollo
Date Available in IDEALS:2016-07-11

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