Home

Applications

ABATTOIRS

     Abattoir wastewaters, say from fowl is particularly difficult to deal with in that it contains a lot of protein and gut waste which is high in nitrogen. The protein is slow to degrade with strong odor potential, as rotting protein tends to have. Cadavarine for example is one of the organic chemicals produced by decaying flesh that gives it the ugly smell.  Many of the abattoirs in the U.S. are using oversized and relatively inexpensive oxidation ditches to process these wastewaters.  

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.

OXIDATION DITCH EQUIPMENT

     Aspiration type units provide good oxygen transfer but also cause a circular pattern of flow through the reactor. This circulation pattern is OK if the basin type requires circulation, such as oxidation ditches and facultative lagoons, but BNR reactors do not need this circulation. Aspiration type aeration devices also provide a high velocity jet that can cause erosion of the bottom or sides of the basin if the basin has a shallow depth or the unit is too close to the side of the berm.

     A typical gear-driven, low speed mechanical surface aerator, a classic oxidation ditch paraphernalia, consists of an electric motor, gearbox, relatively large diameter rotors (say up to 10' or 3.2m), spool and mounting plate for pier-mounted units.  A good quality, low speed unit can and should deliver say about 3.5 lbs O2/hp/hr  in clean water.    .  

     Most types and brands are suitable for AS applications, but each has its own best applications. For example, brush aerators are best for oxidation ditches while fixed diffusers and surface aerators are best for conventional AS systems. The key is to size the unit properly for each application. Once OTR characteristics are established, the sizing is fairly straightforward. Other factors include alpha factor, impact of floc size and settleability, impact on effluent TSS, etc. The key phrase is "if properly sized/selected."

MIXING

     Adequate contact must be provided between organic wastewater constituents and the microorganisms.

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