What is the purpose of the seed in BOD5 testing?

• A. To provide microbial activity necessary for the biological oxidation of organics.
• B. To sterilize the sample.
• C. To increase pH.
• D. To calibrate the thermometer.

Answer: (A)

In BOD5 testing, the seed provides the microbial inoculum that carries out the biological oxidation of organic matter. The test measures how much dissolved oxygen is used by microorganisms as they metabolize organics over five days at a controlled temperature. The sample alone may not have enough active microbes, or the existing microbial population may be slow to respond, so adding a seed ensures there is a consistent, active community of heterotrophic bacteria to drive the oxidation process. This creates a reproducible measure of the sample’s organic strength, since the oxygen demand reflects biological activity rather than a lack of microbes.