Comparison of BOD Exertion in a Simulated
Stream and in Standard BOD Bottles
W. P. ISAACS, Associate Professor
Sanitary Engineering Department
New Mexico State University
University Park, New Mexico
A. F. GAUDY, JR., Professor
Civil Engineering Department
Oklahoma State University
Stillwater, Oklahoma
INTRODUCTION
Today the measurement of changes in dissolved oxygen concentration occurring in a polluted system can be accomplished quite accurately; however, the intricate biological kinetics which determine the course of deoxygenation are at
present only partially explained. First order reaction kinetics have been applied
almost exclusively in the past to describe the exertion of BOD in receiving streams.
The standard BOD bottle test has been used to define biological deoxygenation regardless of the particular process or system being considered, although the technique was originally intended for use in predicting the course of oxygen utilization and oxygen recovery in receiving streams; i. e., in relatively dilute systems.
Its use in conjunction with the reaeration equation has been accepted for many
years to predict the oxygen sag curve in receiving streams. In using the sag
equation, the deoxygenation constant, ki, determined in the BOD bottle, is assumed to be equal to the value of kj in the receiving stream. Most often the re-
aeration constant, k2, is determined indirectly by substituting the value of ki,
determined using the BOD bottle technique, and other parameters into the sag
equation and solving for k2. In general, it may be said that the applicability of
the sag equation has not been experimentally proven for the conditions assumed in
its development, and there are many questionable aspects concerning its applicability. For example, the effect of turbulence and mixing upon metabolic activity
has not been precisely defined, and there is no certainty that the ki value obtained
in the BOD bottle is valid for the receiving stream or for a turbulent system. The
effect of turbulence and mixing on biological activity has received some investigational attention (1, 2); however, the complexity of the problem has made separation of the variables involved quite difficult. Furthermore, the effect of concentration of biological solids or initial seeding concentration on deoxygenation
kinetics has been only partially delineated with respect to kinetic order and kinetic
discontinuities which may appear in the BOD exertion curve (3,4). Also, in
natural streams bacterial deoxygenation and physical reaeration are not the only
factors which contribute to the oxygen balance. Photosynthesis and algal respiration, as well as benthal demands may play an important but as yet relatively unexplored role in determining the course of the DO sag for any particular reach of
stream. It would appear that controlled experimentation in which each of the
contributing mechanisms can be separately studied will almost certainly be required before the most useful equations) of predictive value can be devised.
During the course of an investigation made by the authors to determine factors
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