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DAIRY WASTEWATER

     While dairy wastewater is easy to oxidize, extended aeration experience shows that oxygen requirements of 2 to 2.5 lbO2 per lbBOD are more appropriate.  Because of the rapid rate of oxidation one gets into some of the digestion phases in part of the product.  Also one finds that some of the animal fats don't show up in BOD values while it will break down if you continue to oxidize.  Field experience indicates that the 1.5 to 1.6 lbO2 per lbBOD that is traditional for municipal wastewater will be undersized.  It is therefore recommendable to size equipment based on COD and/or treatability/lab recommendations. .  

     In many plants, including dairy wastes, it is most common to see the bulk of the wastewater contributed in an 8 hour period.  As a result, the oxygen supply rate and any other process hardware on the project must be sized for three (3) times average flow rate - bottom line, wastewater plant must be designed for worst case scenario.

TANNERY WASTEWATER

     General experience with tannery wastewater suggests it can be a very difficult wastewater to handle.  Tanneries usually generate an excessive amount of solids, hair, fats and greases and ... chemicals!  As dumped, massive amounts of lime can create an unstable condition in the wastewater.  In the case of diffused aeration systems, this unstable wastewater can precipitate calcium carbonate on any surface including membranes and diffusers.  This creates back pressure conditions, operating energy increases, and in some cases failure of the membranes.

     It may be possible to fairly/partially get away employing a pretreatment basin ahead of the aerobic biological reactor.  This pretreatment basin would be an anaerobic pond (assuming it to be an acceptable approach) capable of catching all of the floating grease and fat, a high percentage of hair, and a significant portion of any lime precipitate that may be in the wastewater.  Two anaerobic ponds either in series or parallel, say 1.5 to 2 days detention each, would act as a storage for these constituents and eliminate the nuisance conditions prior to the aerobic reactor.  A properly designed anaerobic pond can be very successful in reducing the BOD of the wastewater by at least 50%.  Use of this holding basin prior to the aerobic process will generally minimize any problems with sedimentation of excess solids and minimize the fouling of the diffusers from calcium carbonate precipitate.  It is highly likely membrane material to be almost custom selected for this demanding application.  Please be aware of the likely solids involved.  The pretreatment stage should remove a very high percentage of incoming suspended solids and in fact it is mandatory for proper operation of the aerobic biological reactor - incoming solids are going to fill the basins at a great rate thus the need for redundant parallel basins in handling and managing solids   

     Developing the idea a little bit further an anaerobic pond that has the proper floating cap of grease can be a very effective pretreatment system - warm weather pretreatment ponds with 5-10 days detention could offer BOD removals as much as 50-70%.  Please be aware that COD removals may prove disappointing with typically tricky wastewaters, i.e. tanneries, pulp and paper. 

     As with most industrial wastewaters sizing should be done taking into account COD measurements and actual sampling history/comprehensive wastewater characterization.  Even then an authoritative treatability assessment may be advisable. Figure out the consequences of unhappy engineering sizing an aeration system assuming a BOD/COD ratio of say 0.28 only to later on find it's about 0.5 .. or vice versa..  

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

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

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