Determination of Chemical Oxygen Demand of Industrial Wastewater

Exp 7

What is Chemical Oxygen Demand?

COD is the amount of oxygen required for the complete oxidation of organic and inorganic materials in one liter of wastewater sample by strong chemical oxidizing agents such as acidified K2Cr2O7. COD is expressed in milligrams of oxygen per cubic decimeter of wastewater.

Question 2: What is the role of silver sulfate in the determination of COD?

Silver sulfate acts as a catalyst in the oxidation of straight-chain organic compounds, aromatics, and pyridines.

What is the role of mercuric sulfate in the determination of COD?

What is the role of mercuric sulfate in the determination of COD? Answer: The silver ions in silver sulfate become ineffective in the presence of halide ions (present in wastewater) due to the precipitation of silver halide. This difficulty is overcome by treating the wastewater with mercuric sulfate, which binds the halide ions and makes them unavailable.

What is the indicator used in COD experiment?

Ferrion (1,10-phenanthroline-iron(II) complex) is used as the indicator in this titration.

What is the color change at the endpoint in the determination of COD?

What is the color change at the endpoint in the determination of COD? Answer: The ferrous indicator is intensely red in color. Strong oxidizing agents oxidize the indicator to the iron(III) complex, which is pale blue. As potassium dichromate is present, the indicator remains in the oxidized form, giving a blue color. As the titration continues, the solution becomes blue-green due to the formation of Cr3+ ions from the reduction of Cr2O7^2-. When the potassium dichromate is completely consumed, the indicator is reduced to the iron(II) complex, giving a red-brown color. Thus, the endpoint is marked by the color change from blue-green to red-brown.

Why is sulfuric acid added during the preparation of standard FAS solution?

Sulfuric acid is added to prevent hydrolysis of ferrous sulfate into ferrous hydroxide.

Mention a few applications of the COD test.

COD is an important parameter for industrial-based studies. It indicates the pollution strength of industrial wastes, and COD test results can be obtained quickly.

Question 8: What is the limitation of COD?

COD includes both biologically oxidizable and biologically inert but chemically oxidizable impurities. One limitation of the COD test is that it cannot distinguish between biologically oxidizable impurities and other oxidizable impurities.

Name the possible impurities present in wastewater.

Generally, oxidizable organic impurities in wastewater include straight-chain aliphatic hydrocarbons, aromatic organic compounds, and so on.