The biological oxygen demand (BOD) indicates

Biological Oxygen Demand (BOD): Is defined as ‘amount of oxygen absorbed by a sample of sewage’ during a specified period (Generally 5 days), at a specified temperature (generally 20° C) for aerobic destruction or use of organic matter by living organisms. Strong Sewage has BOD > 300 g/litre and Weak Sewage has BOD < 100 g/litre.