Water and Wastewater.com Help Forums - Low BOD/COD ratio, How to treat?

MDSauns.

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Low BOD/COD ratio, How to treat?
Mar 06^th, 2013, 1:56pm

I am attempting to size aeration equipment for a milk processing plant and am giving effluent limits requirements of both BOD and COD.

My idea of BOD and COD is the following:

BOD: the measure of the amount of oxygen that bacteria will consume while decomposing organic matter under aerobic conditions.
COD: the measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water.

BOD measures the part of COD that can break down biologically (biodegradable). If the BOD to COD ratio is 1:1 than the contaminants are easily biodegradable, but if the BOD to COD ratio is 0 the contaminants are not biodegradable (we cannot treat with aeration). Treating an influent of a .3 BOD/COD or lower usually involves chemical treatment before aerobic processes and/or an increased detention time with anaerobic conditions after the aerobic process.

what I have concluded for now:

If there is a low BOD/COD ratio (0 to 0.3), chemical treatment or increased detention time must be implemented for adequate treatment, since aerobic processes alone will only treat the BOD portion of COD.

I have shared this explanation with some co workers and some disagree.

Can someone please explain to me how to treat water with a low to BOD/COD ratio or just tell me if my explanation is right or wrong?

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grrun God Member Offline WaterandWastewa ter.Com is the best! Posts: 3525 Pekin, IL Gender: Company or Organization: Freelance Environmental Engine	Re: Low BOD/COD ratio, How to treat? Reply #1 - Mar 6^th, 2013, 11:48pm There may be considerable FOG in a dairy plant's wastewater. Removal of the FOG should improve the BOD/COD ratio. Because the FOG is not readily biodegradable but can be oxidized in the COD test; it tends to cause a low BOD/COD ratio. You may want to consider a DAF before biological treatment. grrun
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Muhamad Anas

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Re: Low BOD/COD ratio, How to treat?
Reply #2 - Mar 7^th, 2013, 12:05am

Your understanding about COD:BOD is correct, as the ratio closing to 1 biological process become favorable, it is closer to 0, chemical process is more favorable.

From my understanding, if the BOD5:COD ratio is 0.8, 80% of the BOD can be biologically in 5 days retention time. theoretically of course.

I agree with what Grrunn said that you shoud remove FOG first since FOG can increase COD but will not affect BOD. removing FOG should remove some COD and increase BOD:COD ratio.

Anas.

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Bug Farmer YaBB Newbies Offline I love Water and Wastewater.com Posts: 35 Gender: Company or Organization: Wespoint Home	Re: Low BOD/COD ratio, How to treat? Reply #3 - Mar 7^th, 2013, 2:09am Hi guys, Dear Grrun, As you say dairy product wastewater FOG are slowly biodegradable in nature, my question is that all types of FOG are slowly biodegradable in nature including Edible Oil wastewater ? Regards, Bugs Farmer
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grrun God Member Offline WaterandWastewa ter.Com is the best! Posts: 3525 Pekin, IL Gender: Company or Organization: Freelance Environmental Engine	Re: Low BOD/COD ratio, How to treat? Reply #4 - Mar 7^th, 2013, 11:08am Probably; however you need to define "slowly"in terms of days or years. grrun
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Re: Low BOD/COD ratio, How to treat?
Reply #5 - Mar 11^th, 2013, 6:19am

This wastestream should be expected to be highly biodegradable. As others have pointed out, the fats, oils, and greases may be too slowly degradable to impact the 5 day BOD test. If the waste were to become septic FOGs are degraded to short chain fatty acids which would probably be seen on the BOD test so the answer of if FOG impacts the 5 day BOD is "maybe".

What is the incoming FOG concentration of this waste and what's the BOD and COD? Has anything been done on a lab scale level to simulate treatment?

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