Removal of COD from Waste Water

[Farookengg]

In a Industrial Waste Water,

COD is 480 mg/l &
BOD is 360 mg/l

My understanding is 360 mg/l out of 480 mg/l of COD is Biodegradable & can be biologically oxidized & the remaining 120 mg/l of COD is non biodegradable & need to be oxidized chemically or by Activated Carbon.

Please advise if my understanding is right or not.

 

[bimr]

That is incorrect. Chemical Oxygen Demand is the measure of what is chemically oxidizable of the organics & inorganics present in the wastewater; BOD is a measure of, the amount of the oxygen that is required for the bacteria to biologically oxidize the wastewater.

The ratio of BOD/COD: COD is typically higher than that of BOD; a minimum of 2:1 for municipal wastewater, but varies depending on the industrial process and nature of the raw materials used.

 

[Farookengg]

But I think, Inorganic COD will be very less in the Waste water or any source of water, due to its unstability, so the organic COD that are not biologically oxidized should be non biodegradable COD. Please advise.

 

[bimr]

For normal wastewater, the inorganic COD should be minimal.

The disadvantage of the COD test is that not all of the measured COD can be degraded biologically. There may also be some interferences with the COD test. Low molecular weight fatty acids and aromatic hydrocarbons (organics) may not be well oxidized during a COD test and some inorganic ions (chloride and nitrite) may be oxidized. The addition of catalysts during the COD test may help to eliminate the interferences.

 

[ashtree]

bimr is correct but you should also consider whether your BOD result is Total BOD or BOD5. Total BOD is the total biochemical oxygen demand to completely biologically oxidise the wastewater, whereas BOD5 is a measure of the oxygen that will be required to biologically oxidise the wastewater for the first 5 days.

Different wastewaters will have different relationships between BOD5, TBOD and COD.

TBOD will be closer to COD than BOD5. BOD5 should be less than TBOD. In domestic wastewater BOD5 is likely to be 0.75 or more of the TBOD
but it varies. In industrial wastewater there is sometimes a very large difference between BOD5 and TBOD.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"