Chemical Oxygen Demand

• Introduction

COD stands for Chemical Oxygen Demand.

Waste water consist many harmful ingredients like organic or inorganic wastes which are very harmful for human health and other creatures, to remove this matters we have to oxidised these materials  for oxidation we have need oxygen if these oxygen is provided by using Chemical Oxidising Agent ( Like K2Cr2O7 ).

So in case of COD in spite of  organic Oxygen we use Chemical Oxidising Agents.

• Definition

Amount of the Chemically combined  Oxygen required to oxidised the Organic  (Biodegradable) matters as well as inorganic ( Non-Biodegradable ) matters to make the water pure , is known as Chemical Oxygen Demand ( COD ).

• Some Important Points

1. In COD Potassium Dichromate ( Like K2Cr2O7 )  is used as Oxidising Agent.

2. COD removes both Biodegradable & Non-Biodegradable matters.

3. COD test take three days.

• Difference Between  BOD & COD 

1. BOD removes only Biodegradable Matters but COD removes both Biodegradable &              Non-Biodegradable matters .

2. BOD consumed Organic Oxygen but COD consumed Chemically combined oxygen.

3. BOD test takes 5 days but COD Test Takes 3 days.

4. COD > BOD. COD to BOD ratio range between 1.25 to 2.5  .


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