Aussie:

Of course it will vary, but for example pesticide wastewater can have 6000 ppm BOD, 11,000 ppm COD, and 3500 ppm TOC. So as a rough rule COD is about double the BOD and TOC is almost half the BOD. Other applications can vary. In manure wastewaters, the COD can be 3-5 times higher than the BOD

Cheers!

Greg

Aussiefilf:

The last time I ran a COD was about 13-15 years ago.  We use to utilize a rule of thumb "BOD is about 60% of the COD"  This applies primarily to domestic wastewater and the cleaner industrial samples.  TOC is a different animal for the simple reason that there are different ways of measuring TOC (machine differences as well as methods) and the type of sample.

Hi Aussie,
I guess you will realise from the answers already posted that there is no reliable conversion, (or even "a rule of thumb"), that allows BOD to be converted to COD or BOD to be converted to TOC. The relationship between BOD & COD will vary significantly from wastewater stream to wastewater stream, depending on the processes that give rise to the wastewater.
However, if you are in a position to give details of the processes that give rise the the wastewater of interest to yourself at this time, then maybe we could offer some help.

Fella's,
My situation is this.
I have been given two years worth of BOD data in regards to abattoir wastewater, the state enviromental authority needs a report based on this data but they won't except it as BOD. Only as COD or TOC, go figure!
That is why I'm after conversion ratio's.

cheers

Aussie

Hello every body,

I entered this topic because I am searching an answer to my problem,

testing some Industial wasewater I met some cases that BOD is more than COD
I am sure of the test proccesure and I am looking for Interpritation,

can any one Help?

Envirotic

Here's my 2 cents worth on this.  In my former life in pulp & paper industry, I generally found poor correlation between BOD and COD.  However, excellent correlation was obtained between BOD and soluble COD  (i.e. filtered to remove the pulp fibres).   The correlation was about 2 COD = 1 BOD.

In my present life in meat rendering, I have not been able to obtain a good correlation factor between BOD and either COD or soluble COD, owing to the complexity and ever changing nature of the  wastewater.

I concur with the recommendations of others posted here to run the tests yourself now and see if you can obtain a good correlation.

Sewer_Doc

Envirotic,

These are discharge limits. The reasoning behind the higher BOD limit is that BOD may be relatively easy to degrade further in the environment, but COD (requiring a stronger type of oxidation) may possibly be more difficult to degrade in the environment or in the BOD bottle.
Like many discharge limits, these were arbitraily developed to ensure protection of the environment without a real scientific basis. As chemical analyses become more precise and less expensive, we may someday escape the BOD test which has poor reproducibility and the COD test which provides operators with only vague clues about the quality of the wastewater and the way to prevent or treat harmful discharges.

grrun        

muthee,

This is pure speculation on my part, but fermentation of sugars produce alcohols and organic acids which may inhibit further oxidation. Running the BOD tests out to 20 days may show a change in ratios because there may be a need for the micro organisms to adapt to the changed environment. Seed selection may also affect the BOD results.

I would check these possibilities out before concluding that the waste is not biodegradeable. The alcohols and organic acids would still have significant COD. Therefore. I would insure that I was using an acclimated seed for the BOD tests.

grrun      

Aussie:

There are NO generalized correlations between BOD, COD and TOC. Period! End of story!

As many of the responses to your question have said, you MUST develop your own correlation for your specific waste ... and even that will often not be valid from day to day if the composition of your wastewater is highly variable.

Milt Beychok
(Visit me at www.air-dispersion.com)

Hi,

I strongly agree with mbeychock.

please, do recycle water, do not recycle postings (2004...).

best regards,

DS

Aussie,
I thought I would add a little more info. If you look up in the metcalf and Eddy third addition page 83, it shows ratios of BOD to TOC are 1.0 to 1.6 and BOD to COD varies from .4 to .8. I use .44 for my calculations, but again these ratios vary considerably with the degree of treatment the wastewater has undergone.
dale

I completely agree sludgehound, it's just an estimate. Some one told me that wastewater is not rocket science, I don't think he was trying to insult our intelegence, he was trying to point out in wastewater treatement there is nothing exact due to the complexity of the water coming in, and how it varies in such a wide spectrum. I want to thank all of you for your input and knowledge, you can't get this type of information from a book. thx to all of you.
dale

Absolutely, that's how I do it.

For those who would like to put that famous dutch slogan above the lab door (to remember those who walk trough it): it is not "metend is wetend", but it is: "meten is weten".
Small detail, but in this case, it is better to have it 100.000% right...  

best regards,

DS

what brand for DO meter is good in middle east and whats the required temperature