Which BOD sample specifically requires the addition of seed?

The BOD sample that specifically requires the addition of seed is related to chlorinated effluent. Chlorination can kill off the microorganisms that are necessary for measuring the biochemical oxygen demand (BOD) of a sample. Seed is often added to provide these microorganisms, which serve as a biological population to consume the organic matter in the effluent during the BOD test.

When testing chlorinated effluent, the addition of seed ensures that the sample contains enough active microorganisms to accurately measure its BOD level. The presence of active microbes is crucial for the BOD test, as they are responsible for breaking down organic material and thus consuming oxygen, which is what the BOD measurement is intended to reflect.

For untreated effluent, raw wastewater, and treated wastewater, the microbial populations are usually sufficient to conduct BOD testing without the need for added seed. In those cases, the natural microbial community is viable and can effectively perform the aerobic degradation necessary for the test.