The BOD represents the Biological Oxygen Demand within 5 days in a wastewater sample injected with biomass from an aeration tank. In fact, oxygen is consumed over a period of over 25 days in the wastewater sample. However, oxygen consumption decreases sharply with an increase in time. In the first phase, predominantly substrate/carbon is respired. Subsequently, predominantly endogenous respiration (sludge respiration) takes place. In order not to falsify the result by nitrification, ATH (allythiourea) is added to the sample which inhibits nitritation and thus the entire nitrification.
By limiting the measurement period to 5 days and adding ATH, it is quite possible to reliably determine the biodegradable part of the wastewater and thereby eliminate the proportion for nitrification.
BOD₅ is one of the most important wastewater parameters in terms of sizing and operation of a wastewater treatment plant.


« back