Biochemical oxygen demand

  • Biochemical oxygen demand (BOD, also called biological oxygen demand) is the amount of dissolved oxygen (DO) needed (i.e., demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period.
  • The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20 °C and is often used as a surrogate of the degree of organic pollution of water.
  • BOD can be used as a gauge of the effectiveness of wastewater treatment plants.
 
Why is BOD important?
  • Biochemical Oxygen Demand is an important water quality parameter because it provides an index to assess the effect discharged wastewater will have on the receiving environment.
  • The higher the BOD value, the greater the amount of organic matter or “food” available for oxygen consuming bacteria.
  • If the rate of DO consumption by bacteria exceeds the supply of DO from aquatic plants, algae photosynthesis or diffusing from air, unfavourable conditions occur.
  • Depletion of DO causes stress on aquatic organisms, making the environment unsuitable for life. Further, dramatic depletion can lead to hypoxia or anoxic environments.
  • BOD is also used extensively for wastewater treatment, as decomposition of organic waste by microorganisms is commonly used for treatment.