Biochemical Oxygen Demand (BOD): The amount of Oxygen (mg/1) is taken up by microorganism that decomposes organic waste matter in water. It is therefore used as the measure of the amount of certain types of organic pollutants in water. BOD is calculated by peeping a sample of water containing a known amount of oxygen for 5'days at 20°C in BOD incubator.
Chemical Oxygen Demand (COD) : A parameter of water quality which measures the amount of oxygen in parts per million required to oxidize organic and oxidizable inorganic compounds in the water sample. COD is preferable to the BOD because it is rapidly measurable parameter for river, streams and industrial waste studies and control of water treatment plants.