I am having troubles with Fenton oxidation experiments and I wish to know that what is the wrong I am doing during experiment.
I prepared a KHP sample of 2000 mg/l COD (by dissolving 0.85 g of KHP in 500 ml of distilled water) and use it as the sample for Fenton experiment.
I added 8.688g of FeSO4.7H2O to the above sample and adjust the pH of the solution to
COD measurements are based on the reaction of hexavalent Cr2O7(2-) ion reduction to the trivalent Cr3+ ion in acidic medium. Both FeSO4 and H2O2 are able to reduce Cr((VI). Therefore, you instrument measures the total content of COD + Fe(II) + H2O2
I think that the increase of COD is du to the formation of superoxyle radicals HOO• and hydroxyle radicals HO•, according to the reactions:
1- Fenton reaction: Fe2+(aq) + H2O2 → Fe3+(aq) + OH-(aq) + HO•
2- Formation of superoxyle radicals HOO• and oxygen consomtion (increase):
2HO• + O2→ 2HOO•
3- Formation of hydroxyle radicals HO• : 2HOO• + 2H2O → 2H2O2 + 2HO• →6HO•
4- Note that: 2H2O → 2HO• + 2H•
2HOO• + 2H• → 2H2O2
2H2O2→ 4HO•
I think that the increase of COD is du to the formation of superoxyle radicals HOO• and hydroxyle radicals HO•, according to the reactions:
1- Fenton reaction:
Fe2+(aq) + H2O2 → Fe3+(aq) + OH-(aq) + HO•
2- Formation of superoxyle radicals HOO• and oxygen consomtion (increase):
2HO• + O2→ 2HOO•
3- Formation of hydroxyle radicals HO• :
2HOO• + 2H2O → 2H2O2 + 2HO• →6HO•
4- Note that: 2H2O → 2HO• + 2H•
2HOO• + 2H• → 2H2O2
2H2O2→ 4HO•
Thank you for your replies!
Dear Dr. Yurii V Geletii; Does that mean, in this way after Fenton Oxidation the total COD value of a sample will be increased and we cannot apply Fenton Oxidation for reducing COD of a sample?
Dear Samuel,
The reactions 2 and 3 DO NOT exist! Give the arguments, references or whatever to support your hypothesis.
Dear Disni,
I explain you that your instrument in your system does not measure COD. You can apply Fenton Oxidation for reducing COD of you sample. You need to wait until all H2O2 is consumed and Fe(II) is oxidized to Fe(III) before COD measurement.
Usually the procedure for measuring COD after Fenton experiments is to raise pH to above 10 to precipate iron which instantly stops the Fenton reaction. If Na2CO3 is used to raise the pH it is easier to precipate all Fe(II). Secondly the sample is decanted and then neutralized before H2O2 is removed with catalase. If the sample has a low COD concentration the contribution to COD from the catalase can be determined in a blank sample and subtracted.
This has been discussed in several previous RG questions!
Dear Henrik, could you please post a link about some of the previous RG questions where this topic has been discussed? Thank you in advance,
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