Home

Applications

The following approach can be used to estimate oxygen requirements

Ro = (1 - b * Yg ) * Rs  + b * d * X ,     mg O2/L-hr          
           
 where: 

Rs = rate of COD conversion, mg COD/L-hr (usually COD load * removal efficiency), 
Ro = rate of oxygen uptake, mg/L-hr,
X = microorganism concentration, mgVSS/L
Yg = biomass yield coefficient, mass VSS/mg COD removed (usually 0.3 kg VSS/kg COD removed)
b         = 1.42
d = endogenous decay rate (usually 0.1/day)

     So for 42 mg COD/L-hr maximum COD loading rate ( = 1 g COD/L-d) and an assumed 2,000 mg/L VSS in the mixed liquor and an endogenous decay rate of 0.00417/hr (= 0.1/day), the oxygen uptake rate would be:

Ro = (1 - 1.42*0.3) * (42 * 90%) + 1.42 * 0.00417 * 2000 mg/L = 34 mg O2/L/hr 

     The aeration equipment would have to equal or exceed this rate to insure positive DO in the aeration basin. Of course, you will need to make sure you calculate the loading rates correctly in the zone of interest. For example, for plug flow type processes, the COD loading rate would be that in the first section of the basin. 

     Most manufacturers and equipment vendors have readily available software for preliminary designs and will generally assist you with proper equipment/unit selection including recommended/minimum/maximum depth, oxygen dispersion diameter, complete mix diameter and so on.

     We can't go much higher in MLVSS than about 2,000 mg/L and still get good oxygen transfer in the aeration basins. 

www.AerationFundamentals.com - www.ExtendedAeration.com - www.OxidationDitches.com - www.TricklingFilters.com

www.Biotowers.com - www.MembraneBioreactors.com - www.AnaerobicReactors.com - www.AnaerobicFilters.com 

www.UASBs.com - www.EGSBs.com - www.CoolingTowerFundamentals.com - www.EvaporativeCondensers.com

www.DewateringFundamentals.com - www.BioremediationFundamentals.com - www.IncinerationFundamentals.com