Energy, Total Carbon, and
Oxygen Demand
A. W. BUSCH, Professor of Environmental Engineering
Laboratory of Environmental Science and Engineering
Department of Chemical Engineering
Wm. M. Rice University
Houston,   Texas
The subject of organic pollution measurement is fundamental to water pollution control. Few topics have been so exhaustively treated in the literature. Unfortunately there is still no general acceptance of a procedure of impeccable
competence for all problems. The intent of this paper is twofold: 1) to emphasize
certain concepts held basic to the measurement of organic pollution and 2) to
present data relating to the use of parameters other than oxygen consumption for
organic pollution definition and measurement.
BASIC CONCEPTS IN POLLUTION MEASUREMENT
The work at Rice University for the past eight years (see references 1-15) has
been based on the study of soluble compounds because: 1) soluble constituents are
the only fraction of wastes requiring biological oxidation for their removal, (that
is, suspended and colloidal materials can be removed by physical separation, with
or without the aid of chemical additives such as coagulants); 2) many industrial
wastes are comprised entirely of organics in aqueous solution; 3) effluents from
treatment plants, either industrial or municipal, should contain only soluble organics; and 4) in any situation there is literally no excuse for the discharge of suspended material to a receiving water.
The biodegradable content of a waste can be assessed in two ways: (11)
(1) by measuring the change in organic content effected by bacterial metabolism, or
(2) by measuring the consumption of oxygen by bacteria in effecting the removal of organics.
Because bacterial oxidation is never complete, i.e., some fraction of the
substrate is always converted to cellular components, measurement of oxygen demand is not a complete definition of organic content. The use of oxygen consumption must be in a materials balance context wherein the increase in bacterial
mass is also determined if an accounting for all of the organic material oxidized
is to be made.
The most desirable approach is that of a complete mass balance wherein each
reactant and each product is quantitatively measured.
There are two aspects of the bacterial metabolism of soluble organics of interest; stoichiometry and kinetics. Of these, the stoichiometry is influenced both
by the nature of the substrate and by the system environment. The nature of the
substrate includes such characteristics as complexity of the molecule, bonding
energy and degree of oxygenation. The system environment includes physical
factors such as mixing as well as the ratio of food to organisms. The contrast between chemical reactions and biochemical reactions is clearly indicated by the
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