Operator terms · Wastewater
What is BOD in wastewater?
BOD, biochemical oxygen demand, is the amount of oxygen that microorganisms use to break down the organic matter in water. It is a core measure of how strong or polluted wastewater is: higher BOD means more organic load. Operators track it to judge how well treatment is removing waste.
Last reviewed 2026-08-03
Why it matters
A plant's job is to lower BOD before the water is discharged. Comparing the BOD coming in to the BOD going out shows how well the biological treatment is working.
How it relates to oxygen
If high-BOD water reaches a stream untreated, microbes there use up the dissolved oxygen fish need. That is why removing BOD protects the environment downstream.
Common questions
- What does high BOD mean?
- More organic matter in the water, so a heavier load on treatment.
- Is lower BOD better in effluent?
- Yes. Low effluent BOD means treatment removed most of the organic load.
- How is BOD measured?
- By a standard lab test over five days at a set temperature.