BOD Progression in Soluble Substrates
-IV-
A Short Term Total Oxygen Demand Test
A. W. BUSCH and LESLIE GRADY, JR., Assistant Professors
T. SHIVAJI RAO and E. L. SWILLEY,   Research Assistant
Department of Civil Engineering
Rice University
Houston,   Texas
This paper is the fourth in a series reporting results obtained in an investigation of the biochemical degradation of organic compounds. Previous
papers (1), (2), (3) have defined the progression of BOD in pure soluble organic
substrates, have delineated the oxidation-assimilation relationships, and nave
shown the validity of solids production reactions over the broad range of biological environments. Bacterial growth and cell production have been shown
to reflect the nature of the substrate oxidized, whether in BOD bottles, a Warburg apparatus, or in bio-oxidation systems called activated sludge plants.
This paper shows, for pure soluble organics, how the basic relationships
previously reported may be used for derivation of a short-term TOD test. TOD
is defined as total oxygen demand. It is numerically equivalent to the theoretical oxygen demand. Thus for biologically degradable materials TOD is
numerically equivalent to the COD or chemical oxygen demand.
THEORY
Theoretical oxidation equations can be written for organic compounds.
Thus, glucose has a TOD of 1.07 gm/gm and glutamic acid has a TOD of
0.98 gm/gm. Previous papers (1), (2), (3) of this series have presented evidence that upon attainment of the plateau in the BOD curve, all substrate has
been converted into bacterial cells of known chemical composition (C5H7NO2)
with a theoretical oxygen demand of 1.414 gm/gm. Thus, at the plateau,
the difference between the original substrate TOD and the exerted BOD is contained in cell material. Conversely, for any waste, measurement of plateau
BOD followed by gravimetric or chemical determination of the resulting cell
growth should yield the TOD value of the substrate. Since the plateau occurs
within 24 to 48 hrs there is available a short term TOD test. The short-term
BOD and the TOD values completely define the minimum and maximum
quantities of oxygenwhich must be provided in the treatment plant and/or receiving waters (4). The slope of the short-term BOD curve shows that where
soluble wastes are discharged into streams, use of the currently favored first
order rates of deoxygenation is unduly optimistic and may result in nuisance
conditions.
EXPERIMENTAL PROCEDURE
Theoretically, cell production at the plateau may be measured chemically or gravimetrically. It is pertinent to consider the magnitude of the
COD and/or cell weights involved. Ordinarily only about six mg/l of the
initially present dissolved oxygen can be satisfactorily utilized for bacterial
uptake.   The other 2.5 to three mg/l must be allotted to seed  utilization
-  67  -