Biochemical Oxygen Demand (BOD)

• Introduction

Waste water consist lots of undesirable things which are harmful for humans and others creatures.Harmful things may be Organic or Inorganic,to purify water we have to remove this hazards by oxidised those hazards with the help of microorganisms but for this oxidation we required some amount of oxygen. 

                     The amount of oxygen required to oxidised all the organic as well as inorganic matters is known as Oxygen Demand.

Full form of BOD is Biochemical Oxygen Demand.

• Definition

Oxygen required by the microorganisms to carryout biological decomposition of organic matters under aerobic conditions at standard temperature.

so BOD means the oxygen required only to remove organic wastes.

• Discussion

BOD is classified in two segment-

1. 1st stage BOD (Carbonaceous demand)

2. 2nd stage BOD (Nitrification demand )

Carbonaceous demand means oxygen required to oxidised Carbonaceous matters and Nitrification demand means oxygen required to oxidised Nitrogenous matters.

As the Carbonation starts first it known as 1st stage demand after completion of cardonation Nitrification starts.

See the graph it will be more clear-

• Some Important Points

1. Generally BOD is tasted for 5 days (BOD5).

2. BOD is calculated at a standard temperature of 20 degree celsius.

3. After 6-10 days of Carbonation Nitrification starts.

4. In BOD5 we generally find the Carbonaceous BOD means 1st stage BOD.

5. To get zero BOD it requires infinite time.

6. In 20 days almost 95-99 percent of organic matter oxidised.

• Relation Between DO(Dissolved Oxygen) and BOD

BOD5 (at 20 degree celsius) = [Initial DO - Final DO]x[Dilution factor] 

                                       ( We will discuss about DO and Dilution Factor Later for that Keep Visiting this site )