HIGH-RATE, HIGH-EFFICIENCY DIFFUSED-AIR AERATION SYSTEMS
Boris M. Khudenko, Associate Professor
Department of Civil Engineering
Wayne State University
Detroit, Michigan 48202
Eugene Shpirt, Research Scientist
Division of Laboratories and Research
New York State Department of Health
Albany, New York 12225
Alberto Garcia-Pastrana, Graduate Student
Department of Civil Engineering
Wayne State University
Detroit, Michigan 48202
Diffused aeration is used for various wastewater and sludge treatment processes. The
oxygen requirements for these processes vary from as low as 0.1 kg O^/m /d for slow
processes (for example, extended aeration) to 5 kg 02/m3/d for high-rate industrial wastewater treatment processes and for aerobic sludge stabilization.
The amount of air needed to satisfy oxygen requirements depends on the design parameters of the aeration system: diffuser pore or hole size, geometric parameters of the diffuser
assembly, their location in the aeration tank, the shape and size of the tank, air-flow rate,
physicochemical properties of the aerated liquid, and the dissolved-oxygen concentration
in the liquid.
Sizing of aeration systems requires determination of the relationships between these
parameters. Such relationships can be found by the use of the theory of similarity. Though
a total similarity of the model and full-scale processes cannot be reached, approximate
modeling can give satisfactory results.
The purpose of this paper is to develop, on the basis of a review of the literature and the
authors' own research results, relationships among design parameters of diffused-air systems
which will allow the designer to size diffused-air systems for treatment processes under a
wide range of oxygen requirements.
Considering the fact that existing theories of the hydrodynamics of heterogenous flows
and mass-transfer processes complicated by reactions do not allow one to describe the
aeration process theoretically, a combined experimental and analytical method was used
in this study. The study consisted of the following major stages:
1. conventional "clean water" non-steady-state testing of aerators (at this stage the data on
effects of geometric and dynamic characteristics of the system on the mass-transfer coefficient and the oxygen equilibria concentration were collected);
2. experimental evaluation of the effects of admixtures and water temperature on the mass-
transfer coefficient and the oxygen equilibrium concentration;
3. analysis and generalization of experimental data;
4. field testing and validation of the relationships developed at previous stages; and
5. development of a rational design procedure for sizing diffused-air systems.
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