BOD stands for biological oxygen demand. It is the amount of oxygen required for aerobic biological microorganisms (bacteria that require free oxygen for growth) to decompose organic material in a given water source at a certain temperature over a given time period. In waste treatment language, BOD is most frequently stated as the percentage of waste removed or remaining after treatment. COD stands for chemical oxygen demand. It is a measurement of the oxygen required to oxidize soluble and particulate organic matter in water using a strong oxidizing agent. The COD level can be determined more readily than BOD, but this measurement does not indicate how much waste can be decomposed by biological oxidation.