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Andres

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method to determine COD "type"?
Mar 14^th, 2012, 9:14am

Hello,

Might be a really newbe (and fuzzy) question but, today I got some meeting notes of water treatment option and it was mentioned that in order to model the process, we need to know what type of COD is in the water? I understand, that part of COD is the BOD, but what else might it refer to?

As far as I understood, it is needed to determine if AnBo and ABO treatment is enough or we need an AOP system.

Question: Does that mean that we need to know the quantitative composition of the contaminaited water? Or there is some other way to find know what will/can be removed in bio after pretreatment?

Thank you in advance and hope the question is not confusing to you as it is to me,

Andres

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Also, if anyone can suggest some big engineering-consulting company, that could model us a treatment plant and that has experince in cleaning highly contaminaited water, I will be thankful for the contact. Basicly, we have In and Out parameters, but need the method, model and someone to construct.

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H2O_Tech Junior Member Offline Water and Wastewater.com is the best! Posts: 86	Re: method to determine COD "type"? Reply #1 - Mar 14^th, 2012, 11:58am Hello Andres, Here's a good link from the University of WI:http://dnr.wi.gov/org/water/wm/ww/biophos/3fract.htm Unsure of your location, but I work with CDM, CH2MHill, Black and Veatch on lots and lots of projects all over the world. Just 3 of many.
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Re: method to determine COD "type"?
Reply #2 - Mar 14^th, 2012, 1:00pm

Souble COD (BOD) is the portion of the chemicals that will pass through a Millipore filter. Bacteria can readily assimulate the soluble portion of these chemicals. However, some soluble portion of the chemicals such as long chain polymers may require longer times for breakdown for biological consumption. The COD is a very severe oxidation process which will oxidize particulate as well as soluble chemicals and that is one of the reasons that COD is usually greater than BOD (assuming only a 5 day BOD test). Anyway, soluble COD is used to estimate the food for activated sludge processes.

grrun

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sobisch

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Re: method to determine COD "type"?
Reply #3 - Mar 15^th, 2012, 2:31am

Dear Andres,

this is a very important question, though often overlooked.
If the COD has good degradability it is not so much important, however, if problematic it matters very much.
At least you should have an idea, which are the compounds of concern.
Their chemical/physical nature gives you the clue to an approach to solve the problem. This may vary between adsorption, chemical oxidation, reduction, volatilization etc. depending on COD composition.

Kind regards
T. Sobisch

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Andres

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Re: method to determine COD "type"?
Reply #4 - Mar 15^th, 2012, 6:30am

Thank you all for your great replies!

Did I understand correctly, that Soluble COD = BOD? And that is the value I would have to look for (BOD5)? If so, it does not make sense to me - we had provided both COD and BOD values.

I thought that almost all BOD will be "eaten" in a bioreactor.

Also, did I understand correctly, that if, say, we tested the water and got 1000 COD and 700 BOD, after biotreatment (assuming all the BOD got degraded), the COD will be 300 and BOD=0?

Or did I miss something?

Andres

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sobisch God Member Offline Posts: 1777 Gender: Company or Organization: L.U.M. GmbH	Re: method to determine COD "type"? Reply #5 - Mar 15^th, 2012, 6:48am one is chemical the other biological oxygen demand. COD might be determined after filtration (soluble) or without (soluble + dispersed).
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DoctorBug

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Re: method to determine COD "type"?
Reply #6 - Mar 15^th, 2012, 10:20pm

Andres:

Many wastewater treatment models require the soluble COD (or soluble BOD). This is because the particulat COD (or BOD) is slowly degraded, usually within the flocs. In many treatment plants, the particulate COD (or BOD) is wasted out of the system unoxidized in the waste sludge and the degradation is continued later in an aerobic or anaerobic digester. Models usually use the soluble BOD (or COD if this is all that is available) because of this.

Hope that this helps.

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Andres

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Re: method to determine COD "type"?
Reply #7 - Mar 16^th, 2012, 1:43am

Once again a fact smarter! Thank you.

It is strange, that during all the 5 years in the university we were not told about soluble and insoluble COD and BOD. Not once.

So will it be reasonable to check for Soluble COD(BOD) part when doing analysis. Will try to find out who does it locally. The lab we usually work with does only COD and BOD7.

Thank you!

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DoctorBug Senior Member Offline Water and Wastewater.com is the best! Posts: 498 Company or Organization: Michael Richard Wastewater Mic	Re: method to determine COD "type"? Reply #8 - Mar 16^th, 2012, 1:59am Andres: The soluble BOD or COD is merely the sample filtered through a 0.5 um pore-size membrane filter. The filtrate is then tested just like the normal BOD or COD. Expect less though. Hope that this helps.
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Andres YaBB Newbies Offline I love Water and Wastewater.com Posts: 40 Gender: Company or Organization: Tallinn University of Technol.	Re: method to determine COD "type"? Reply #9 - Mar 16^th, 2012, 3:29am DoctorBug, I understood that, thank you. Just it is not on the offered analysis list. Might need just to ask.
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Re: method to determine COD "type"?
Reply #10 - Apr 20^th, 2012, 4:12am

I finally got the results:
The "normal" COD is 34 g/L
The soluble COD is 32 g/L

After reading this post by Dan Keys, am I correct to assume, that DAF unit might remove the 2 g/L? (the difference between normal and soluble)

Quote:

For example, if all of the COD/BOD is dissolved sugar with no suspended solids, the DAF will do nothing at all. But if most of the COD/BOD is in the form of biodegradable suspended solids, the DAF will remove most of it.

Andres

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Jeff Naumann

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Re: method to determine COD "type"?
Reply #11 - Apr 20^th, 2012, 7:45am

Andres wrote on Apr 20^th, 2012, 4:12am:

I finally got the results:
The "normal" COD is 34 g/L
The soluble COD is 32 g/L

After reading this post by Dan Keys, am I correct to assume, that DAF unit might remove the 2 g/L? (the difference between normal and soluble)

Quote:

For example, if all of the COD/BOD is dissolved sugar with no suspended solids, the DAF will do nothing at all. But if most of the COD/BOD is in the form of biodegradable suspended solids, the DAF will remove most of it.

Andres

MIGHT is correct. But, it also MIGHT NOT remove the rest.

But, another factor is that from your particular example, with BOD=32 and COD=34, is that the error range from those tests means that there is really no significant difference. If you performed another set of tests on your sample you might get BOD=35 and COD=36. The test for BOD, particularly, is not very precise.

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argfin

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Re: method to determine COD "type"?
Reply #12 - Apr 20^th, 2012, 8:26am

Andres wrote on Apr 20^th, 2012, 4:12am:

I finally got the results:
The "normal" COD is 34 g/L
The soluble COD is 32 g/L

After reading this post by Dan Keys, am I correct to assume, that DAF unit might remove the 2 g/L? (the difference between normal and soluble)

Quote:

For example, if all of the COD/BOD is dissolved sugar with no suspended solids, the DAF will do nothing at all. But if most of the COD/BOD is in the form of biodegradable suspended solids, the DAF will remove most of it.

Andres

Hi Andres,

In theory that remaining after filtration is 'solids'. However, if you look at a 0.45um filterpaper, it looks like a solid 'plastic' disc compared to the normal everyday fibrous discs you get. Therefore the residual solids might be tiny particles barely visible to the human eye, and might be too small for a DAF to remove efficiently. Even after coagulation / polymers, etc.

Also as Jeff mentions you would also need to establish and the accuracy and 'limit of detection' from your laboratory. The limit might be affected by any dilutions that were necessary, the type of test, e.g. titration or quick colorimetric vial digestion, etc.

I ran some quick tests years ago with COD dilutions and a x10 dilution made the final result +/- 300mg/l, with smaller dilutions causing less and less error.

It is also a well know fact that such tests are highly variable and a bank of data should be built up over time. Point data are fairly useless in the grand scheme of things.

Regards,
argfin

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