Biochemical oxygen demand (BOD) is a measure of how much organic pollution is in water. The BOD test measures the amount of dissolved oxygen in water that is used up due to the breakdown of organic pollutants, such as sewage, in a certain number of days. Raw sewage has a BOD of forty to 150 milligrams per liter, whereas drinking water has a BOD of less than 0.5 milligrams per liter.
Engineers and scientists measure the BOD of a lake or river to see how healthy the water is. The lower the BOD, the healthier the water. Water needs to have oxygen in it to support aquatic life such as fish and plants. Oxygen in the water is replenished from the atmosphere through aeration, but if it is used up faster than it is replenished, the water becomes anaerobic (or hypoxic)— existing in the deficiency or absence of free oxygen. Anaerobic water cannot support life. see also Fresh Kills; Hypoxia; Water Treatment.
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