- Alkaline-iodide-azide solution
- Manganese sulphate
- Con. Sulphuric acid
- Starch solution
- 0.025N sodium thiosulphate
- BOD bottle
- Water bottle
- Measuring cylinders
- BOD Incubator
- Burette and burette stand
- Standard flask
- Magnetic stirrer
- Stir bar
- Glass funnel
- Glove box
- Tissue paper
- Collect the water sample from a pond.
- Carefully fill a BOD bottle with sample water without making air bubbles.
- 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.
- Add 2 mL of alkali-iodide-azide reagent 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 2ml of Conc.H2SO4 carefully without forming air bubbles.
- Close the bottle and mix the solution well to dissolve the precipitate.
- Keep the bottle in BOD incubator for 5days of incubation.
- After incubation, titrate 50 ml of sample water with 0.025N Sodium thiosulphate to a pale yellow color.
- Then add 2ml of starch solution. So the sample turns blue in color.
- Continue the titration till the sample gets clear and note the readings.
- The concentration of dissolved oxygen in the sample is equivalent to the number of milliliters of titrant used.