The biochemical oxygen demand (BOD) determination is an
empirical test in which standardized laboratory procedures are
used to determine the relative oxygen requirements of wastewaters,
effluents, and polluted waters. The test has its widest application
in measuring waste loadings to treatment plants and in
evaluating the BOD-removal efficiency of such treatment systems.
The test measures the molecular oxygen utilized during a
specified incubation period for the biochemical degradation of
organic material (carbonaceous demand) and the oxygen used to
oxidize inorganic material such as sulfides and ferrous iron. It
also may measure the amount of oxygen used to oxidize reduced
forms of nitrogen (nitrogenous demand) unless their oxidation is
prevented by an inhibitor. The seeding and dilution procedures
provide an estimate of the BOD at pH 6.5 to 7.5.
Measurements of oxygen consumed in a 5-d test period (5-d
BOD or BOD5, 5210B), oxygen consumed after 60 to 90 d of
incubation (ultimate BOD or UBOD, 5210C), and continuous
oxygen uptake (respirometric method, 5210D) are described
here. Many other variations of oxygen demand measurements
exist, including using shorter and longer incubation periods and
tests to determine rates of oxygen uptake. Alternative seeding,
dilution, and incubation conditions can be chosen to mimic
receiving-water conditions, thereby providing an estimate of the
environmental effects of wastewaters and effluents.
The UBOD measures the oxygen required for the total degradation
of organic material (ultimate carbonaceous demand)
and/or the oxygen to oxidize reduced nitrogen compounds (ultimate
nitrogenous demand). UBOD values and appropriate kinetic
descriptions are needed in water quality modeling studies
such as UBOD:BOD5 ratios for relating stream assimilative
capacity to regulatory requirements; definition of river, estuary,
or lake deoxygenation kinetics; and instream ultimate carbonaceous
BOD (UCBOD) values for model calibration.