Answer:
BOD (Biochemical Oxygen Demand):
- The total quantity of dissolved oxygen utilized by aerobic bacteria for the decomposition of biodegradable organic matter present in a water sample is called BOD.
- Example of aerobic bacteria: Pseudomonas, Bacillus, or Escherichia coli.
COD (Chemical Oxygen Demand):
- The amount of oxygen required to chemically oxidize all types of organic matter—whether biodegradable or non-biodegradable—present in a water sample is called COD. In this, the strong oxidizing chemical potassium dichromate is utilized.
Difference between BOD and COD:
Biochemical Oxygen Demand (BOD):
- This is used to determine the amount of biodegradable pollutants in water. Aerobic bacteria are utilized.
- The amount of dissolved oxygen in water utilized by bacteria during this process is called BOD.
- The value of BOD is always less than COD, when the water is from a single source.
- The unit of BOD is mgO2/ltr.
Chemical Oxygen Demand (COD):
- This is performed to determine the quantity of both types of pollutants, biodegradable and non-biodegradable, in water. Potassium dichromate is utilized in this.
- During the decomposition process, whatever amount of dissolved O2 in water is utilized by this chemical is called COD.
- The value of COD is always greater than BOD.
- The unit of COD is mgO2/ltr.
⇒ Both of these indicate how much quantity of organic pollutants is present in water, but their method and analysis of measurement are different.