Q. What is the role of ultraviolet (UV) radiation in the water purification systems?
- It inactivates kills the harmful microorganisms in water.
- It removes all the undesirable odours from the water.
- It quickens the sedimentation of solid particles, removes turbidity and improves the clarity of water.
Which of the statements given above is/are correct? (UPSC Prelims 2012)
Answer:
1 only
Notes: The correct answer is
[A] 1 only. Ultraviolet (UV) radiation is a physical disinfection method used in water treatment. It specifically utilizes the UV-C spectrum (wavelengths between 200 nm and 280 nm) to target the biological contaminants in water.
- Inactivation of Microorganisms (Statement 1 is Correct): UV radiation works by penetrating the cell walls of microorganisms like bacteria, viruses, and protozoa (including Giardia and Cryptosporidium). The energy disrupts their DNA or RNA, preventing them from reproducing. Since a microorganism that cannot reproduce cannot cause infection, it is considered "inactivated" or "killed" for practical purposes.
- Removal of Odours (Statement 2 is Incorrect): UV radiation is a physical process and does not involve chemicals or adsorption. It does not remove dissolved organic compounds, hydrogen sulfide, or other chemicals that typically cause unpleasant tastes or odours. For odour removal, technologies like Activated Carbon filters or Ozonation are required.
- Sedimentation and Turbidity (Statement 3 is Incorrect): UV light has no impact on the physical suspended solids in water. It does not act as a coagulant or flocculant to quicken sedimentation. In fact, high turbidity (cloudiness) actually hinders UV purification because suspended particles can "shield" microorganisms from the UV rays, a phenomenon known as shadowing. Pre-filtration is usually necessary to ensure the water is clear before it enters the UV chamber.