Biochemical Oxygen Demand

    In order to survive in a waterway, plants and animals demand oxygen from the water. BOD is a measurement of how much stress is being placed on the dissolved oxygen system of water. The lower the BOD, the more oxygen remains dissolved in the water and is available for fish and other aquatic organisms. A higher BOD indicates that a large amount of organic matter is present in the water, and the aquatic life that relies on the dissolved oxygen will die.

    A BOD value of 1 ppm is excellent and the water is considered "pure." A BOD value of 2ppm is good and a value of 3 or 4 ppm is fair. Therefore the smaller the BOD, the higher the water quality.

Procedures:

· To measure BOD, wait 5 days after the dissolved oxygen test at the river.

· Then follow the same procedures as the dissolved oxygen test with a sample brought back from the river.

· Once an average is found, subtract it from the DO value found 5 days earlier. The difference is the BOD.