Consider the following statements:

1. The quality of waste water is determined on the basis of DO.

2. The BOD test is based on DO.

3. Determination of DO helps in controlling corrosion.

Which of the above statements are correct?

The maximum amount of oxygen that can be dissolved in water is called Saturated dissolved oxygen. Any deficiency of oxygen from its saturated value indicates the presence of organic matter in water and hence, quality of waste water, in which main source of pollutant is organic matter, can be determined on the basis of DO.

BOD is the amount of oxygen required to carry out the decomposition of organic matter in water is called BOD. In BOD test, waster water sample is initially diluted with aerated water and after dilution its DO value is noted. After that, diluted sample is kept for incubation of 5 days at 20⁰ C to determine the final value of DO. The difference between initial and final value of DO indicates the BOD of the given water sample. Hence, the BOD test is based on DO.

Excess of dissolved oxygen in the water causes the hydroxide(s) to oxidize further to produce final corrosion product, iron oxide.Apart from this corrosion is caused by presence of CO₂ in water and hence, presence or absence of CO₂ in water indicates degree of corrosion potential of water.