How does biochemical oxygen demand measure wastewater pollution?

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Aerial view of wastewater treatment basins with circular clarifiers; overlaid toilet graphic and arrow with text reading: “Where does it go?” — wastewater treatment All the sewers in your neighborhood end up here.

Biochemical oxygen demand (BOD) measures wastewater pollution by quantifying the amount of dissolved oxygen consumed by microorganisms as they metabolize organic matter in the water.1

In the context of wastewater treatment, this metric serves as a reliable indicator of organic pollution levels. The relationship functions as follows:1

Higher Organic Content: Increased levels of organic matter, such as those found in sewage, lead to a higher BOD.1
Oxygen Depletion: As microorganisms consume more oxygen to break down this matter, the amount of dissolved oxygen available for aquatic life, such as fish, decreases.1
Treatment Goal: A primary objective of treating wastewater before it enters a water resource is to reduce its BOD, thereby preventing the depletion of oxygen in receiving streams, lakes, and rivers.1