Disinfection destroys all microorganisms.

• A. True
• B. Only for some organisms
• C. False
• D. Depends on the disinfectant used

Answer: (C)

Disinfection in wastewater treatment is about reducing the number of pathogens to a level considered safe, not about destroying every microorganism. Some organisms are more resistant to common disinfectants, and certain conditions can limit effectiveness. For example, spores and some protozoan cysts (like Cryptosporidium and Giardia) can survive chlorination, and high turbidity or organic matter can shield microbes from inactivation. The effectiveness of a disinfectant also depends on dose, contact time, temperature, pH, and proper operation. Because of these factors, disinfection aims to achieve regulatory-safe reductions rather than complete sterilization of all microorganisms.