6. (a) State THREE types of micro-organisms that may exist in water.(3)
(b) Describe, with the aid of a sketch, the operation of a Silver Ion Sterilizer.(7)
(a) Types of micro-organisms in water (3 marks)
- Bacteria – e.g., E. coli, Legionella, pathogenic organisms.
- Viruses – microscopic agents that can cause disease (e.g., Hepatitis A).
- Protozoa – single-celled organisms such as Giardia or Cryptosporidium.
(b) Operation of a Silver Ion Sterilizer (7 marks)
Principle of operation:
- A Silver Ion Sterilizer kills bacteria by releasing controlled amounts of silver ions (Ag⁺) into the water stream.
- These ions interfere with enzyme systems and cell walls of microorganisms, preventing reproduction and causing death.
Construction & Operation:
- The sterilizer consists of a chamber fitted in the water pipeline.
- Inside are silver electrodes connected to a low-voltage DC power supply.
- As water flows through, a small current passes, releasing silver ions into the water.
- The silver ions mix uniformly, maintaining a residual bactericidal effect throughout the storage and distribution system (unlike UV which has no residual effect).
- Ion concentration is carefully controlled (typically ≤ 0.1 mg/L) to ensure safe potable water quality.
- Monitoring instruments may be fitted to ensure proper dosing.
Sketch (exam-style, line diagram):
- Show a water pipe with a sterilizer chamber.
- Inside: two silver electrodes connected to a DC supply.
- Arrows: water in → treated water out.
- Label: “Release of Ag⁺ ions into flow for sterilisation.”