Hi
my name is Nick and I am going to teach you how to test for B.O.D (biochemical
oxygen demand). When organic matter decomposes, it is fed upon by aerobic
bacteria. In this process, organic matter is broken down and oxidized (combined
with oxygen). Biochemical oxygen demand is a measure of the quality of oxygen
used by these microorganisms in the aerobic oxidation of organic matter.
When
aquatic plants die, they are feed upon by aerobic bacteria. The input of
nutrients into a river, such as nitrates and phosphates, stimulate plant growth.
Eventually, more plant growth leads to more plant decay. Nutrients, then, cane
be a prime contributor to high biochemical oxygen demand in rivers.
Impounded
river reaches also collect organic wastes from up river that settle in quieter
water. The bacteria that feeds on this organic wastes consume oxygen. Percent
saturation (dissolved oxygen) values in water with much plant growth and decay
often falls below 90 percent.
The way you test for BOD is a water sample with out any air bubbles and
drop in two tablets from the Lamotte’s test kit. Wait tell the tablets
dissolve; it takes about five minutes. Then check the color with the color chart
in the kit and determine the level of oxygen and ppm. Collect samples and return
to the class room and check the level of oxygen in five days to see if any
microbes have consumed any oxygen.