This document discusses chemical oxygen demand (COD) testing. COD testing measures the amount of organic matter in water by determining the oxygen required to chemically oxidize the matter. Potassium dichromate is commonly used as the strong oxidizing agent. The COD test procedure involves refluxing a water sample with dichromate and sulfuric acid, then titrating the remaining dichromate with ferrous ammonium sulfate to determine the COD level in mg/L. COD testing provides faster results than biochemical oxygen demand (BOD) testing and oxidizes a wider range of compounds, though the results do not directly correlate to 5-day BOD levels.

1. CHEMICAL OXYGEN
DEMAND
Presented By :-
RAJNEESH KUMAR GAUTAM
MTECH 1ST SEM (ENERGY
&ENVIRONMENT)
BABA SAHEB BHIM RAO AMBEDKAR
UNIVERSITY-LUCKNOW 226001

2. INTRODUCTION
The organic matter present in sewage can be
measured in number of ways. Organic matter is
often assessed in terms of oxygen required to
completely oxidise the organic matter to CO2 ,
H20 and other oxidised species.
The oxygen required to oxidise the
organic matter present in a given waste water
can be theoretically calculated .If the organic
compounds and their concentration are known
the oxygen demand of the sample can be
accurately computed but it is impossible to

3. know the details of organic compounds Present
in raw water or waste water. The COD is
therefore determined by performing a laboratory
test On given water sample using a strong
oxidant like dichromate solution.
It is expressed in milligrams per liter (mg/L) also
referred to as ppm (parts per million), which
indicates the mass of oxygen consumed per liter
of solution.

4. DEFINITION
COD is the total amount of oxygen required to
chemically oxidize the bio degradable and non-
biodegradable organic matter.

5. HISTORY
• Earlier potassium permanganate was used
as an oxidizing agent
• COD values were very much lower than that
of 5th day BOD
• It indicated that potassium permanganate
was not very effective in oxidizing all the
organic matter present
• After that other oxidizing agents like ceric
sulphate, potassium iodate and potassium
di-chromate were also used

6. HISTORY (cont.)
• Potassium di chromate was found to be the
most effective due to
- Completely oxidize all organic matter
- Relatively cheap
- Easy to purify

7. COD TEST BY DICHROMATE
PRINCIPLE
• Water sample is refluxed in strong acidic
solution with a known excess amount of
potassium dichromate.
• After digestion, the remaining unreduced
K2Cr2O7 is titrated with Ferrous Ammonium
Sulfate (FAS)to determine K2Cr2O7
consumed.
• This gives us the oxidizable organic matter in
terms of oxygen equivalent.

8. TEST PROCEDURE
1. Wash 300 ml round bottom refluxing flask.
2. In refluxing flask put one spatula of HgSO4 +
10 ml sample + 5ml K2Cr2O7 + 15 ml
concentrated H2SO4.
3. Add small amount of silver sulphate
4. Shake well and reflux for 2 hr.
5. Cool and add little amount of distilled water
to the flask through the condenser

9. TEST PROCEDURE (CONT.)
6. Titrate the solution in the flask against FAS
using Ferroin indicator
7. End point green color to reddish brown
NOTE: For blank, add 10 ml distilled water
instead of sample. Rest of the procedure is the
same.

10. CALCULATIONS
• The COD in mg/l is determined by the
formula,
COD mg/l = (A-B)xNx8000
ml sample taken
A = ml of FAS required for blank.
B = ml of FAS requires for sample.

11. ADVANTAGES OF COD TEST
• COD result are available much sooner than
BOD test results.
• The COD test requires fewer manipulations
of the sample.
• The COD test oxidizes a wide range of
chemical compounds.
• It can be standardize more easily.

12. DISADVANTAGES OF COD TEST
• The major disadvantage is that the results
are not directly applicable to 5-day BOD
results without correlation studies over a
long period of time.
• One more limitation of COD is it’s inability to
differentiate between biologically oxidizable
and biologically inert organic matter.

13. References
• Journal on industrial waste water treatment
by k.l moed
• Environmental engineering vol 1&2 by S.K
Garg
• Industrial waste water treatment by metcalf
& eddy