Chemical Oxygen Demand

1. Assignment:
Chemical Oxygen Demand:
( Environmental Engineering)
Submitted by:
Salma iqbal(E37):
Session (2015-2019)
8th
semester
Submitted to:
Mam Anum Khalid
College of Earth and Environmental
Sciences:

2. Cod:
The chemical oxygen demand (COD) is an indicative measure of the amount
of oxygen that can be consumed by reactions in a measured solution.
It is commonly expressed in mass of oxygen consumed over volume of
solution which in
SI units are milligrams per litre (mg/L).
A COD test can be used to easily quantify the amount of organics in water.
The most common application of COD is in quantifying the amount of
oxidizable pollutants found in surface water (e.g. lakes and rivers)
or wastewater. COD is useful in terms of water quality by providing a metric
to determine the effect an effluent will have on the receiving body, much
like biochemical oxygen demand (BOD).
PRINCIPLE:
The chemical oxygen demand (COD) determines the amount of oxygen
required for chemical oxidation of organic matter using a strong chemical
oxidant, such as, potassium dichromate under reflux conditions.
Apparatus:
 Cod flask
 China dish measuring cylinder
 Cod reactor
 Oven
 Potassium Dichromate
 Sodium nitrate.
 Distilled water
 Water sample
 Conical flask
 Sulphuric acid
 Water bath.
Procedure:
o Water sample is collected from a pond.
o Poured 10ml of water sample in three 100 ml conical flask.
o Simultaneously the distilled water is taken in three 100ml conical
flask labeled as Blank1, Blank2 and Blank3.

3. o Added 5ml of potassium dichromate solution in each of the six
conical flasks
o Keep the flask in water bath at 100°C (boiling temperature) for 1 hour
o Allowed the samples to cool for 10 minutes
o Added 5ml of potassium iodide in each flasks
o Added 10ml of sulphuric acid in each flask
o Titrated the contents of each flask with 0.1N Sodium thiosulphate
until the blue colors disappear completely.
Why we need to do cod?
Chemical Oxygen Demand is an important water quality parameter because,
similar to BOD, it provides an index to assess the effect discharged
wastewater will have on the receiving environment.The COD test is often used
as an alternate to BOD due to shorter length of testing time.
Which is the best method to remove cod from waste water?
Coagulation may be the best way to reduce cod from waste water .
which method is best to determine cod from wastewater
The most common test method is the colorimetric analysis after oxidizing
the COD with acid and using indicator compounds, such as hexavalent
dichromate.
The End