Editing Biochemical oxygen demand (section)

== Test limitations ==
The test method involves variables limiting reproducibility. Tests normally show observations varying plus or minus ten to twenty percent around the mean.<ref name="Hammer">{{cite book | author=Hammer, Mark J. | title=Water and Waste-Water Technology | year=1975 |publisher=John Wiley & Sons | isbn=978-0-471-34726-2}}</ref>{{rp|82}}

=== Toxicity ===
Some wastes contain chemicals capable of suppressing microbiological growth or activity. Potential sources include industrial wastes, [[antibiotic]]s in pharmaceutical or [[medical waste]]s, sanitizers in food processing or commercial cleaning facilities, [[Water chlorination|chlorination]] disinfection used following conventional sewage treatment, and odor-control formulations used in sanitary waste holding tanks in passenger vehicles or portable toilets. Suppression of the microbial community oxidizing the waste will lower the test result.<ref name="Hammer" />{{rp|85}}

=== Appropriate microbial population ===
The test relies upon a microbial ecosystem with enzymes capable of oxidizing the available organic material. Some waste waters, such as those from biological secondary [[sewage treatment]], will already contain a large population of microorganisms acclimated to the water being tested.  An appreciable portion of the waste may be utilized during the holding period prior to commencement of the test procedure.  On the other hand, organic wastes from industrial sources may require specialized enzymes.  Microbial populations from standard seed sources may take some time to produce those enzymes. A specialized seed culture may be appropriate to reflect conditions of an evolved ecosystem in the receiving waters.<ref name="Hammer" />{{rp|85–87}}