procedure recommended and adopted by the
Association of Official Analytical Chemists
(AOAC) is a 5-day incubation period and is
referred to as the 5-day BOD, or BOD 5. This
value is only an index of the amount of
biodegradable organic matter, not an actual
measure of organic waste.
Domestic sewage that contains no indus-
trial waste has a BOD of approximately 200
ppm. Food processing wastes are normally
higher and frequently exceed 1,000 ppm.
Table 12–1 gives the typical amount of
BOD 5 and suspended solids from food and
related industries. Note that the BOD data
and values for suspended solids generally
show a parallel relationship. However, BOD 5
is not as closely related to dissolved solids.
Although BOD is a common measure-
ment of pollution of water and the test is rel-
atively easy to conduct, it is time-consuming
and lacks reproducibility. Tests such as
chemical oxygen demand (COD) and total
organic carbon (TOC) are quicker, more reli-
able, and more reproducible.
Chemical Oxygen Demand. The COD test
for measuring pollution strength oxidizes
compounds chemically rather than biologi-
cally by a dichromate (K 2 Cr 2 O 7 ) acid reflux
method. Because it is a chemical analysis,
this test also measures non-degradable mate-
rials, which are not measured by BOD test-
ing. When a plant monitors effluent to be
discharged for municipal treatment, daily
COD measurements can serve as a guide to
determine whether and when a biological or
chemical effluent could create a treatment
problem at the wastewater treatment plant.
This test, however, gives no indication as to
whether the organic matter can be degraded
biologically and, if so, at what rate. Some
molecules are not oxidized as a result of this
type of treatment. Although overlapping
occurs, this test does not duplicate the
BOD 5. Data from the COD test closely
relate to dissolved organic solids. Unless a
ratio has been established for COD/BOD,
regulatory agencies have not accepted COD
data as a substitute for BOD data in the past.
Dissolved Oxygen. Dissolved oxygen (DO)
concentration is of major concern for both
wastewater and receiving water because it
affects aquatic life and is important in treat-
ment systems such as aerated lagoons. Deter-
mination of dissolved oxygen can be
accomplished by an iodometric titration pro-
cedure using the azide and permanganate
procedures to remove interfering nitrite and
ferrous ions, even though this method is not
considered to be very reliable. Alternatively,
electrode probes can be used for this meas-
urement. They are faster and more conven-
ient than the iodometric tritrimetric method
and more adaptable for use in most indus-
trial wastewaters. However, certain metal
ions, gaseous oxidants stronger than molecu-
lar oxygen, and high concentrations of
cleaning compounds will interfere with the
electrode probes used to measure dissolved
oxygen.
Total Organic Carbon. Total organic car-
bon determines all materials that are
organic. It measures the amount of CO 2 pro-
duced from the catalytic oxidation at 900ºC
of solid matter in wastewater. This method
of pollution measurement is rapid and216 PRINCIPLES OFFOODSANITATION
Table 12–1Typical Composition of Wastes from
Food and Related Industries
BOD 5 Suspended
Type of Waste (ppm) Solids (ppm)Dairy and milk 670 390
products
Food products 790 500
Glue and gelatin 430 300
Meat products 1,140 820
Packing house and 590 600
stockyard waste
Rendered products 1,180 630
Vegetable oils 530 475