Correct Answer - Option 2 : Dissolved oxygen
Concept:
Winkler’s method:
The Winkler Method is a technique used to measure dissolved oxygen in freshwater systems. Dissolved oxygen is used as an indicator of the health of a water body, Where higher dissolved oxygen concentrations are correlated with high productivity and little pollution. This test is performed on-site.
Steps for Winkler’s method:
- Carefully fill a 300mL BOD bottle with sample water.
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Immediately add 2mL of manganese sulfate to the collection bottle and Add 2 mL of the alkali-iodide-azide reagent in the same manner. If white ppt form then there will be no DO present and if brown ppt form then Do will be present.
- Place the stopper and shake it to mix well.
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Add 2 mL of concentrated sulfuric acid via a pipette shake it to mix well again.
- Take a 201ml sample in a glass flask and add 2 ml of the starch solution so blue color forms.
- Titrate with sodium thiosulfate until the blue colour disappears.
- The concentration of dissolved oxygen in the sample is equivalent to the number of milliliters of titrant used.
Dissolved oxygen(DO):
Dissolved oxygen (DO) is a measure of how much oxygen is dissolved in the water. The amount of dissolved oxygen in a stream or lake can tell us a lot about its water quality. For the survival of fish in a river stream, the minimum dissolved oxygen is prescribed 4 mg/l.
Chemical oxygen demand(COD):
- It is the amount of oxygen required to carry out the decomposition of biodegradable organic matter and non-biodegradable organic matter present in the wastewater.
- It is determined by adding potassium di-chromate and sulfuric acid in the water and nothing down the amount of oxygen consumed for the decomposition of organic matter.
Bio-Chemical oxygen demand(BOD):
- It is the amount of oxygen required for the decomposition of biodegradable organic matter present in the system.
- BOD during 5 days at 200C is concerned as the standard BOD and is approximately 68% of the ultimate BOD.
