Disinfection of water by the addition of small amounts of chlorine or a chlorine compound.

• A. Chlorination
• B. CBOD
• C. Biomass
• D. Blank

Answer: (A)

Disinfection of water by adding small amounts of chlorine or a chlorine compound is chlorination. This process uses chlorine to form reactive species that oxidize and inactivate pathogens, providing a protective residual in the water to prevent recontamination as it moves through pipes. It’s favored in many systems because it’s fast, effective, and easy to monitor for safety and residual levels.

CBOD refers to carbonaceous biochemical oxygen demand, which measures how much oxygen will be consumed by microorganisms to break down organic matter—an indicator of pollution, not a disinfection method. Biomass means the total mass of microorganisms present, not a disinfection process. Blank would imply no process at all, which isn’t describing disinfection.