Studies on the Causation of Phasic
Oxygen Uptake in High Energy Systems
M. N. BHATLA, Research Assistant
A. F. GAUDY, JR., Professor
Bioengineering Laboratories
School of Civil Engineering
Oklahoma State University
Stillwater, Oklahoma
During the last decade the diphasic nature of the expression of carbonaceous
BOD has been recognized. More recently it has been observed that a plateau in
accumulated oxygen uptake can occur separating the two phases of oxygen utilization. It is this latter finding which has emphasized the need to re-evaluate
present concepts of BOD kinetics. Many investigators agree that the first stage of
O2 uptake corresponds to assimilation of the exogenous carbon sources, and the
second to endogenous respiration of the organisms which have grown up during the
first phase. However, relatively little is known about the existence, the general
occurrence, or the reason(s) for the pause or plateau which often occurs between
the two phases.
Efforts to gain an insight into these aspects have precipitated a fairly large-
scale research effort in our laboratory. In general, two experimental approaches
have been used in these investigations. First it was necessary to establish the
range of conditions under which the plateau occurred and the generality of its occurrence. In accomplishment of this aim approximately fifty long-term BOD experiments were conducted in which the time course of BOD exertion and changes
in the viable bacterial population were studied. Experiments were conducted in
which the type and the concentration of seed material were varied. These experiments included investigations using various pure compounds as sole carbon sources,
mixtures of pure compounds, and whole wastes. In the great majority of cases a
plateau in BOD exertion was observed between two distinct phases of oxygen uptake. In general the first phase corresponded to a rapid growth of bacterial cells,
the pause or plateau to the range of the maximum population, and the second
phase of oxygen uptake to a decrease in viable count. These results established
that a plateau could be observed under a wide variety of conditions, and analysis
of the oxygen uptake and count data led to the formulation of theories of causation for the existence of the plateau. These results have been reported in a series
of papers, (1,2,3,4). The major emphasis in approach then shifted to studies into
the causation for the plateau, and examination of the second stage of oxygen uptake in relation to the theories postulated as a result of our previous work.
REVIEW OF LITERATURE
A number of laboratories have been active in recent investigations of BOD
kinetics, and it is appropriate to review this work as it bears upon reasons for the
occurrence of the plateau. Busch (5) concluded that oxygen uptake which occurred
after reaching the plateau was due to both endogenous respiration and oxygen
utilization by predators, i.e., protozoa. He felt that the bacteria-protozoa relationship in the inoculum was a decisive factor in the clear expression of the
plateau. However, Wilson and Harrison (6) obtained a two-phase oxygen uptake
curve,  i.e.,  two phases separated by a plateau,  using a pure culture inoculum
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