biochemical oxygen demand

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The amount of oxygen required by aerobic microorganisms to decompose the organic matter in a sample of water, such as that polluted by sewage. It is used as a measure of the degree of water pollution.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The amount of oxygen needed by aerobic microorganisms to decompose all the organic matter in a sample of water; it is used as a measure of pollution.