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Chemical Oxygen Demand (COD) Determination in Industrial Waste Water

N

nidhir

#1
Dear all,
We currently use APHA method to determine COD in waste water. However, in the sample preservation method, there is a requirement to bring the ph < 2by acidification with sulphuric acid.
Our concern with this issue is that :
1. The industrial effluent may contain leachate which reacts with the acid and is dangerous for the sampler.
2. The effluent is at aroud 40 degress Celcius during sampling, hence adition of acid causes a very exothermic reaction, once again dangerous for the sampler and may be affecting other parameters to be tested.
Could someone help on these two issue.
Thanks
 
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Ajit Basrur

Staff member
Admin
#2
Dear all,
We currently use APHA method to determine COD in waste water. However, in the sample preservation method, there is a requirement to bring the ph < 2by acidification with sulphuric acid.
Our concern with this issue is that :
1. The industrial effluent may contain leachate which reacts with the acid and is dangerous for the sampler.
2. The effluent is at aroud 40 degress Celcius during sampling, hence adition of acid causes a very exothermic reaction, once again dangerous for the sampler and may be affecting other parameters to be tested.
Could someone help on these two issue.
Thanks
Nidhir,

Question 1 - I am not sure.

Question 2, the samples have to be cooled to 4 deg C at time of sample collection.

Being a weekend, the response is slow. Let us wait for some experts to chip in early next week :)
 
#3
HI

I used to be a chemist once upon a time. My answers to your questions may be useful still.

1. If you suspect that acidification of the effluent may lead to emission of toxic substances (e.g. HCN), you can carry out the operation in a laboratory hood, wearing the right nose mask.

2. Addition of concentrated Sulphuric acid to water leads to generation of heat; a pH of 2 can be achieved by using dilute sulphuric acid (approx. 10 % sulphuric acid) without generating much heat. You don't need to add a large volume of the acid to water to get a pH of 2; a drop or two should be enough for say 50 ml of water (pH 7) to get a pH of 2.

Please do the sample preservation yourself and you will see that is not difficult.

With kind regards

Ramakrishnan
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#4
Dear all,
We currently use APHA method to determine COD in waste water. However, in the sample preservation method, there is a requirement to bring the ph < 2by acidification with sulphuric acid.
Our concern with this issue is that :
1. The industrial effluent may contain leachate which reacts with the acid and is dangerous for the sampler.
2. The effluent is at aroud 40 degress Celcius during sampling, hence adition of acid causes a very exothermic reaction, once again dangerous for the sampler and may be affecting other parameters to be tested.
Could someone help on these two issue.
Thanks
Just a point of clarification, as I am not a chemist, others here are and will respond.

This is not for US EPA Water Sense?
 
H

huntpeter

#6
HI

I used to be a chemist once upon a time. My answers to your questions may be useful still.

1. If you suspect that acidification of the effluent may lead to emission of toxic substances (e.g. HCN), you can carry out the operation in a laboratory hood, wearing the right nose mask.

2. Addition of concentrated Sulphuric acid to water leads to generation of heat; a pH of 2 can be achieved by using dilute sulphuric acid (approx. 10 % sulphuric acid) without generating much heat. You don't need to add a large volume of the acid to water to get a pH of 2; a drop or two should be enough for say 50 ml of water (pH 7) to get a pH of 2.

Please do the sample preservation yourself and you will see that is not difficult.

With kind regards

Ramakrishnan
I agree with you.
 
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