INitrifying bacteria grow slowly, more slowly than the microorganisms that oxidize organic matter, and it normally takes from 6 to 10 days before they start to consume oxygen. However, as shown in the figure below, if a significant number of nitrifying bacteria are present in the wastewater, they might exert sufficient oxygen demand to introduce error even into the measurement of organic matter using the BOD5 test. In these cases, the wastewater sample being tested should be pretreated with an agent that suppresses nitrifying bacteria, and the results of the BOD test should be reported as CBOD (carbonaceous BOD).