Biological+Oxygen+Demand+(BOD)

=Biological Oxygen Demand (BOD)=


 * Many biological (organic) pollutants (such as waste from farm land) decomposes in water and will use up dissolved oxygen in the water when they do this.
 * The amount of oxygen the pollutant needs (or demands) is called the BOD and this is measured over a period of 5 days.
 * Water naturally contains small amounts of organic waste that has a BOD of up to about 1ppm.
 * If other organic pollutants are added it may rise above 5ppm. This would decrease the oxygen content of water from 9ppm to about 4ppm and the water would no longer be able to sustain aquatic life.
 * Water can naturally re-dissolve oxygen in it. The faster it flows the quicker this happens due to the increased surface area in content with the air.