Why adding seed into the sample in BOD5 test?

Adding seed into the BOD5 test sample introduces a known quantity of microorganisms that can degrade organic matter. This helps create a consistent baseline for measuring the biochemical oxygen demand, as the seed provides a reliable source of bacteria to assess the oxygen consumption over the five-day period. The inclusion of seed also ensures that the test results are not solely dependent on the microorganisms present in the sample, which may vary widely in concentration and activity.