Biological oxidation demand is determined by

(D) Organic matter # Biochemical oxygen demand (BOD) is the amount of oxygen absorbed by a sample of sewage during a specified period at a specified temperature for the aerobic destruction or use of organic matter by living organisms. BOD > 300 mg/L is 'strong' sewage; BOD < 100 mg/L is 'weak' sewage. It is due to organic matter present in the sewage.