The biomass in an activated sludge plant consumes large amounts of oxygen for the degradation of wastewater pollutants (carbon, nitrogen). The oxygen consumption is comprised of the proportion for the direct oxidation of the pollutants (substrate respiration) and the basic underlying oxygen consumption of the biomass (endogenous respiration).
Endogenous respiration in nitrifying municipal activated sludge plants is in the range of 0.4 mg O2 / g oSS min, while typical operating values are in the range of 1 - 3 mg O2 / g oSS min. It should be noted that the operating values are measured with substrate limitation (effluent concentration). If the substrate concentration (no limitation) is increased in laboratory experiments, maximum respiration rates can be measured, which are higher by a factor of 3 to 5 .


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