Water treatment fundamentals: Disinfection of drinking water is primarily performed to remove or inactivate which contaminant class?

Introduction / Context:
In conventional treatment trains (coagulation–flocculation–sedimentation–filtration–disinfection), each unit targets a different contaminant class. Disinfection is the last barrier that inactivates disease-causing microorganisms to protect public health.

Given Data / Assumptions:

• Treated municipal water prior to distribution.
• Standard disinfectants (e.g., chlorine, chloramines, ozone, UV) are considered.
• Filtration and clarification steps precede disinfection for turbidity control.

Concept / Approach:

Disinfection specifically targets microorganisms (bacteria, viruses, protozoa). High turbidity and colour are addressed earlier because they shield microbes and consume disinfectant. Odour may be reduced incidentally by oxidation but is not the primary objective of disinfection.

Step-by-Step Solution:

Verification / Alternative check:

Standards (e.g., CT concept for chlorine/UV) quantify pathogen inactivation, confirming that disinfection’s performance metric is microbial reduction, not turbidity or colour removal.

Why Other Options Are Wrong:

• Turbidity, odour, colour: primarily handled by coagulation, filtration, activated carbon, or oxidation upstream.
• “All the above” overstates the scope of disinfection.

Common Pitfalls:

• Assuming chlorine will “clean everything.” It is a microbial barrier, not a solids filter.
• Ignoring the impact of turbidity on disinfectant demand and efficacy.

Final Answer:

Bacteria and other pathogens.