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A Simplified Physical Model for Studying Assimilative Capacity W. E. GATES, Assistant Professor F. G. POHLAND, Associate Professor School of Civil Engineering Georgia Institute of Technology Atlanta, Georgia K. H. MANCY, Assistant Professor F. R. SHAFIE, Research Fellow School of Public Health The University of Michigan Ann Arbor, Michigan INTRODUCTION Considerable effort has been expended in an attempt to define and evaluate the assimilative capacity of natural waters. Most of these endeavors have utilized dissolved oxygen depletion and/or replenishment as the indicating parameter. Consequently, when dealing with streams, it is generally accepted that the assimilative capacity refers to the oxygen which is available to the biosphere, from or through the hydrosphere, within selected constraints. Because the dissolved oxygen content of the hydrosphere is a renewable resource, assimilative capacity is primarily controlled by the rates, the relative rates, and the changes in the rates which dictate the oxygen transfer from the atmosphere to the hydrosphere (surface reoxygenation) and from the hydrosphere to the biosphere (deoxygenation). The net effect of the interplay of these factors is usually considered to produce the classical concept of the oxygen sag curve (Figure 1). The sag curve, thus, reflects the impact which the deoxygenation processes have on the dissolved oxygen concentration of the hydrosphere when the buffering capability of reoxygenation is considered. If the rates of deoxygenation exceed those of reoxygenation the curve demonstrates a negative slope, and if the magnitude of the rates is reversed, a positive slope prevails. The minimum point, which is an inherent characteristic of such curves, represents the dissolved oxygen concentration which must be compared with the selected constraints. When the dissolved oxygen concentration of a slug of water in a stream is measured at different times as the slug travels downstream, the resulting values represent the actual balance which is being effected between the deoxygenation and reoxygenation processes. However, as with any engineering problem, the emphasis is not on measuring the event, but on being able to predict it accurately. If the sag curve can be adequately predicted, then the required degree of waste water treatment becomes known and it is then also possible to make Doth an optimum use and equitable allocation of the oxygen resources of a stream. In order to be able to predict exact values of the oxygen sag curve requires that one also be able to predict the rates of reoxygenation and deoxygenation. The latter implies that the parameters which control these rates are both identifiable and determinable. As previously mentioned, in situ measurements are excellent for describing the balance which is produced, however, they provide very little information as to the exact nature of the two component processes. That is, such determinations relate only indirectly to the separate processes and, also, they represent the results of studying a unique set of environmental conditions. It would be - 665 -
Object Description
Purdue Identification Number | ETRIWC196656 |
Title | Simplified physical model for studying assimilative capacity |
Author |
Gates, W. E. Pohland, Frederick G., 1931- Mancy, K. H. Shafie, F. R. |
Date of Original | 1966 |
Conference Title | Proceedings of the 21st Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://earchives.lib.purdue.edu/u?/engext,12965 |
Extent of Original | p. 665-687 |
Series |
Engineering extension series no. 121 Engineering bulletin v. 50, no. 2 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-05-20 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 665 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | A Simplified Physical Model for Studying Assimilative Capacity W. E. GATES, Assistant Professor F. G. POHLAND, Associate Professor School of Civil Engineering Georgia Institute of Technology Atlanta, Georgia K. H. MANCY, Assistant Professor F. R. SHAFIE, Research Fellow School of Public Health The University of Michigan Ann Arbor, Michigan INTRODUCTION Considerable effort has been expended in an attempt to define and evaluate the assimilative capacity of natural waters. Most of these endeavors have utilized dissolved oxygen depletion and/or replenishment as the indicating parameter. Consequently, when dealing with streams, it is generally accepted that the assimilative capacity refers to the oxygen which is available to the biosphere, from or through the hydrosphere, within selected constraints. Because the dissolved oxygen content of the hydrosphere is a renewable resource, assimilative capacity is primarily controlled by the rates, the relative rates, and the changes in the rates which dictate the oxygen transfer from the atmosphere to the hydrosphere (surface reoxygenation) and from the hydrosphere to the biosphere (deoxygenation). The net effect of the interplay of these factors is usually considered to produce the classical concept of the oxygen sag curve (Figure 1). The sag curve, thus, reflects the impact which the deoxygenation processes have on the dissolved oxygen concentration of the hydrosphere when the buffering capability of reoxygenation is considered. If the rates of deoxygenation exceed those of reoxygenation the curve demonstrates a negative slope, and if the magnitude of the rates is reversed, a positive slope prevails. The minimum point, which is an inherent characteristic of such curves, represents the dissolved oxygen concentration which must be compared with the selected constraints. When the dissolved oxygen concentration of a slug of water in a stream is measured at different times as the slug travels downstream, the resulting values represent the actual balance which is being effected between the deoxygenation and reoxygenation processes. However, as with any engineering problem, the emphasis is not on measuring the event, but on being able to predict it accurately. If the sag curve can be adequately predicted, then the required degree of waste water treatment becomes known and it is then also possible to make Doth an optimum use and equitable allocation of the oxygen resources of a stream. In order to be able to predict exact values of the oxygen sag curve requires that one also be able to predict the rates of reoxygenation and deoxygenation. The latter implies that the parameters which control these rates are both identifiable and determinable. As previously mentioned, in situ measurements are excellent for describing the balance which is produced, however, they provide very little information as to the exact nature of the two component processes. That is, such determinations relate only indirectly to the separate processes and, also, they represent the results of studying a unique set of environmental conditions. It would be - 665 - |
Resolution | 300 ppi |
Color Depth | 8 bit |
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