BOD Progression in Soluble Substrates -
VIII—The Quantitative Error Due to
Nitrate as a Nitrogen Source
J. W. LEWIS, USPHS Trainee
A. W. BUSCH, Associate Professor of Environmental Engineering
Department of Chemical Engineering
Rice University
Houston, Texas
INTRODUCTION
The oxidation of carbonaceous organics by biological action is an autocata-
lytic oxidation-reduction reaction which may be ultimately characterized by the
equation:
_       .        _ bacteria
Organics + Oxygen >    Carbon Dioxide + Water and which may be
nutrients
bacteria
represented by any intermediate time by: Organics + Oxygen  > Carbon
nutrients
dioxide + Bacteria + Water
Thus,  the measurement of the amount of oxygen required in the oxidation of a
waste is a logical characterization of the waste.
The biochemical oxygen demand test (BOD) is one of the most widely applied control parameters in waste treatment and water pollution control. The test
attempts to determine the pollutional strength, or oxygen equivalent, of a substrate by measuring the oxygen utilized by a biological mass, mainly bacteria,
in the oxidation of the carbonaceous organics present. The test has evolved over
many years, replacing such measures as the relative stability test and the potassium nitrate oxygen demand test. In attempts to simulate natural stream conditions, many studies were carried out over the years with regard to the bacterial
seed to be used, the mechanics of the test, and the salt content of the dilution
water. Early in the development of the test it was realized that ammonia and
nitrate in the sample could be oxidized and cause erroneously high values for the
carbonaceous BOD. Methods such as pasteurization of the sample, inhibition of
nitrifiers, and elimination of excess nitrogen from the dilution water have been
advocated for the prevention of errors resulting from nitrification (1).
Ordinarily the BOD test is run for five days, terminated, and ultimate or
20-day BOD values calculated. An excess of ammonia nitrogen is usually present
but the five-day period is considered too short for significant nitrification to take
place (2). In the study of complex industrial wastes the BOD test is frequently
extended to twenty days and nitrification is definitely a problem (3).
Gaffney and Ingols have proposed substituting nitrate nitrogen for ammonia
in the BOD dilution water in order to prevent nitrification (3).   Nitrate is being
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