Principle

BOD is a titration test. BOD stands for Biochemical Oxygen Demand. It is a measure of the amount of oxygen required for aerobic bacteria to decompose organic matter in water.

The Indian Standard for drinking water does not specify an acceptable limit of BOD in water. However, drinking water should have a BOD level below 1 mg/L.

Calibration

No calibration is needed for this test.

Test

This test uses the BOD reagents.

  • Collect the water sample from a pond.
  • Carefully fill a BOD bottle with sample water without making air bubbles.
  • Add 40 drops of Reagent A to the BOD bottle. To ensure that no bubbles are formed, carefully insert the pipette just below the surface of the water.
  • Add 40 drops of Reagent B to the BOD bottle in the same manner.
  • Close the bottle and mix the sample by inverting many times. A brownish cloud will appear in the solution as an indicator of the presence of Oxygen.
  • Allow the brown precipitate to settle out to the bottom.
  • Add 40 drops of Reagent C to the BOD bottle without forming any bubbles.
  • Close the bottle and mix the solution well to dissolve the precipitate.
  • Titrate 50 ml of the water sample with BOD titrant till it reaches a pale yellow colour.
  • Add 40 drops of Reagent D to the titrate so that the sample turns blue in colour.
  • Continue the titration till the sample turns clear and note the readings.
  • From the home screen choose Titration Test > Water > Dissolved Oxygen and enter the titration result.
  • This should give you the initial DO in mg/L.
  • Keep the bottle in a BOD incubator for 5 days of incubation.
  • After incubation, repeat the titration in a similiar manner and note the readings.
  • From the home screen choose Titration Test > Water > Dissolved Oxygen and enter the titration result.
  • This should give you the final DO in mg/L.
  • Now, BOD can be calculated from the difference between initial and final DO.