Which substance should not be used to seed BOD water?

In the context of seeding biochemical oxygen demand (BOD) tests, the ideal seeding material should provide a consistent and representative microbial population that can effectively demonstrate the potential for organic matter degradation. Industrial effluent is often unsuitable for this purpose because it may contain toxic substances, inhibitory compounds, or variable and non-representative microbial communities that can lead to skewed results.

The other options, such as fresh settled domestic wastewater, sewage sludge, and raw sewage, typically contain a more balanced and robust microbial population that is more appropriate for accurately measuring BOD. These materials usually harbor a diverse range of microorganisms capable of breaking down organic pollutants, thus offering a better foundation for the test. In contrast, the composition and characteristics of industrial effluent can significantly alter the microbial dynamics, making it challenging to gauge biological activity and organic load accurately.