Nitrate versus Oxygen Respiration in the Activated Sludge Process

In this study biokinetic and microbial growth coefficients for nitrate versus oxygen respiration in the activated sludge process were evaluated and compared. Two bench-scale activated sludge units were operated over a range of mean cell residence times and under the same conditions except that one unit was aerobic and the other was anoxic. The maximum microbial yield coefficient, ${\rm Y}_{{\rm max}}$, and the endogenous decay coefficient, ${\rm k}_{{\rm d}}$, were lower and the maximum substrate utilization rate, k, was higher for nitrate respiration versus oxygen respiration. COD removal efficiencies were nearly equal at corresponding mean cell residence times. Sludge production was approximately 40% smaller for anoxic conditions when compared to aerobic conditions for similar mean cell residence times less than 10 days.