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Biological Oxygen Demand


Adobe Flash EOL

Animation link: https://vlab.amrita.edu/repo/BIOTECH/ECO/Biological_Oxygen_Demand/index.swf


Materials required


  • Alkaline-iodide-azide solution
  • Manganese sulphate
  • Con. Sulphuric acid
  • Starch solution
  • 0.025N sodium thiosulphate
  • BOD bottle
  • Water bottle
  • Pipettes
  • Measuring cylinders
  • BOD Incubator
  • Burette and burette stand
  • Standard flask
  • Magnetic stirrer
  • Stir bar
  • Glass funnel
  • Gloves
  • Glove box
  • Tissue paper




  1. Collect the water sample from a pond.
  2. Carefully fill a BOD bottle with sample water without making air bubbles.
  3. Add 2ml of manganese sulfate to the BOD bottle carefully by inserting the pipette just below the surface of water. So that you can avoid the formation of air bubbles.
  4. Add 2 mL of alkali-iodide-azide reagent in the same manner.
  5. 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.
  6. Allow the brown precipitate to settle out to the bottom.
  7. Add 2ml of Conc.H2SO4 carefully without forming air bubbles.
  8. Close the bottle and mix the solution well to dissolve the precipitate.
  9. Keep the bottle in BOD incubator for 5days of incubation.
  10. After incubation, titrate 50 ml of sample water with 0.025N Sodium thiosulphate to a pale yellow color.
  11. Then add 2ml of starch solution. So the sample turns blue in color.
  12. Continue the titration till the sample gets clear and note the readings.
  13. The concentration of dissolved oxygen in the sample is equivalent to the number of milliliters of titrant used.







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