What is the correct order of treating hard groundwater, from initial step to final step in a typical treatment plant?

(A) Disinfection

(B) Softening

(C) Aeration

(D) Filtration

Choose the correct answer from the options given below :

The correct answer is - (C), (B), (D), (A)

Key Points

• Aeration
  • Aeration is the first step in treating hard groundwater. It involves exposing water to air to remove dissolved gases such as carbon dioxide and to oxidize dissolved metals like iron and manganese.
  • This process improves the taste and removes odors from the water.
• Softening
  • The next step is softening, which involves the removal of hardness-causing minerals, primarily calcium and magnesium.
  • This is often achieved by using lime or ion-exchange resins to precipitate or exchange these minerals.
• Filtration
  • Filtration is the third step and is used to remove particulate matter from the water.
  • This can involve various methods such as sand filters, membrane filters, or other media to physically remove particles.
• Disinfection
  • The final step is disinfection, which involves killing or inactivating pathogenic microorganisms to ensure the water is safe for consumption.
  • Common disinfection methods include chlorination, UV radiation, and ozonation.

Additional Information

• Purpose of Aeration
  • Removes dissolved gases such as hydrogen sulfide and radon.
  • Oxidizes dissolved metals, making them easier to remove in subsequent steps.
• Water Softening Techniques
  • Ion Exchange: Uses resins to exchange hardness ions (calcium and magnesium) with sodium or potassium ions.
  • Lime Softening: Adds lime (calcium hydroxide) to precipitate calcium and magnesium as carbonate compounds.
• Filtration Methods
  • Sand Filtration: Utilizes a bed of sand to capture and remove suspended particles.
  • Membrane Filtration: Employs semi-permeable membranes to separate particles based on size and charge.
• Disinfection Methods
  • Chlorination: Adds chlorine to kill bacteria and viruses.
  • UV Radiation: Uses ultraviolet light to inactivate microorganisms by damaging their DNA.
  • Ozonation: Introduces ozone gas, which is a powerful oxidant that destroys pathogens.