Biochemical oxygen demand

Biochemical Oxygen Demand (BOD) is a measure of the quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter.

Introduction

Biochemical Oxygen Demand (BOD) is a critical parameter in water quality and waste water treatment, indicating the amount of organic matter present in water. It is defined as the amount of oxygen required by aerobic microorganisms to decompose the organic matter in a sample of water under specific conditions.

Measurement

The BOD value is most commonly expressed in milligrams of oxygen consumed per liter 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. This method is commonly known as BOD5.

Applications

BOD is used as a gauge of the effectiveness of wastewater treatment plants. It is listed as a conventional pollutant in the U.S. Clean Water Act. High BOD levels indicate an abundance of biodegradable material that consumes oxygen as it decays. If the BOD level in water is high, the amount of dissolved oxygen (DO) can decrease to levels that are harmful to aquatic life.

Factors Affecting BOD

Several factors can influence BOD levels. These include temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the water.

See Also

• Chemical Oxygen Demand
• Dissolved Oxygen
• Water Pollution
• Wastewater Treatment

References

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  BOD test bottles (biological oxygen demand)

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  Influent raw wastewater (note grey colour in glass jar)

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  Disposable BOD Bottles

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  BOD Bottle

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  Dissolved oxygen sensor in a sewer treatment plant