Talk:Chemical oxygen demand

Bula — Preceding unsigned comment added by 27.123.136.171 (talk) 14:51, 1 September 2022 (UTC)

Untitled
Here at CAI, we make premade reagents for the COD test using potassium dichromate and mercury (II) sulfate as the chloride precipitator.This article refers to the "permanganate" mehtod as an alternative to the dichromate method.

Can anyone provide us with more information? We want to develop new products for the COD test that are accurate and precise, but free of the hazardous mercury waste. mgilbert@caisc.com


 * Alghough I wrote this article, I'm not an expert in the field (at the time I just happened to be having a lengthy conversation about COD/BOD with my girlfriend, who is a civil/environmental engineer; later I filled in the article from a few of her textbooks). Not being an expert won't prevent me from giving casual advice, however :-)


 * From what I've heard about potassium permanganate, while it's a strong oxidizing agent, it doesn't appear to completely oxidize all organic compounds (hence BOD values are often higher than COD when using KMnO4). So it's unlikely that the permanganate method is valid for all samples. Plus, it seems to me that you'd still end up with chloride interference, which would again probably require the use of mercuric sulfate. Back to square one.


 * I've heard that there are ways to eliminate mercury from samples by precipitating it as mercuric iodide, which I believe is harmless. If I recall correctly, potassium iodide may be used for the precipitation, and may recover 70% to 80% of the mercury. (A quick Google search shows that these folks also suggest potassium iodide and say you can get up to 95% recovery.) It seems that this would be worth checking into. Best wishes, Diberri | Talk 19:17, Aug 30, 2004 (UTC)

Ammonia Contribution
The article states that oxidation of ammonia is part of the COD reaction, but I don't believe that this is generally considered to be the case. Free chloride ions can lead to the oxidation of ammonia, but under typical conditions these are controlled and ammonia oxidation should be minimal.


 * If you can provide a reference for that, please feel free to update the article. --David Iberri (talk) 02:34, 27 May 2006 (UTC)

COD of oil and grease
I heard that in actual municipal wastewater, for each mg/L of oil&graease there are about 12 mg/L of COD. I don't see how it comes from the equation, but I see it in actual lab result. Maybe someone knows about it? I also added the wastewater application to article. hope its OK with you.84.229.159.187 (talk) 20:26, 30 October 2011 (UTC)


 * I suspect something wrong in the lab. A typical paraffin will have a COD value slightly less 4 times the molecular weight. For example decane which has a molecular weight of 142 will require 496 grammes of oxygen for complete oxidation.  Velella  Velella Talk 23:35, 30 October 2011 (UTC)

mg/L and ppm are not the same
The first paragraph in the article infers that mg/L and ppm are interchangeable as units (meaning they are the same thing), which they are not. For this reason the reference to ppm should be removed. The mg/L expression is a mass per volume expression, while ppm is a dimensionless expression (made possible because the units used on either side of the expression are the same, i.e. litres per megalitre, milligrams per kilogram etc). A common problem occurs when ppm and mg/L are interchanged unwittingly when, for example, working out the dose rates of chemicals in water. Take the example of dosing 42% ferric chloride in water (a common occurrence in the treatment of industrial discharge waters). Since the specific gravity of 42% ferric chloride is 1.45, then 1 litre of 42% ferric chloride is equal to 1.45 kilograms. When 1 litre of 42% ferric chloride solution is dosed into 1,000,000 litres of water, the dose rate is 1 ppm. If I then reported this as 1 mg/L, I would clearly be wrong (since it is 1.45 mg/L). Hence one cannot just call mg/L as ppm (or vice versa) else in this case a 45% error will occur! BluesLewis (talk) 07:40, 24 September 2015 (UTC)
 * I agree with you. I have never seen COD expressed as ppm and have removed it from the first paragraph. EvM-Susana (talk) 22:13, 26 September 2015 (UTC)

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