Water treatment basics: Chlorination of drinking water is primarily carried out for the removal and inactivation of which constituent?

Introduction / Context:

Chlorination is one of the most common disinfection processes used in municipal water treatment plants and distribution systems. The objective is to inactivate disease-causing organisms to protect public health, while also maintaining a residual to prevent recontamination in the network.

Given Data / Assumptions:

• Treated water requires microbiological safety before supply.
• Chlorination is applied after clarification and filtration in conventional treatment trains.
• The question focuses on the primary purpose of chlorination.

Concept / Approach:

Chlorine (and chlorine-based disinfectants) inactivates bacteria, viruses, and some protozoa by oxidative reactions that damage cell membranes and disrupt enzymatic and reproductive functions. This significantly reduces waterborne disease risk. Chlorination does not remove turbidity (suspended solids), minerals that cause hardness, or settleable sediments; those are treated by sedimentation, filtration, and softening processes.

Step-by-Step Solution:

Verification / Alternative check:

Standard water treatment references list disinfection (microbial control) as the fundamental role of chlorination. Secondary benefits such as taste/odor control can occur but are not the main purpose.

Why Other Options Are Wrong:

• Suspended solids / Sediments: Removed by coagulation-flocculation and sedimentation/filtration, not chlorine.
• Hardness: Addressed by lime-soda softening, ion exchange, or membrane processes.
• Dissolved metals: May require oxidation/filtration or sequestration; chlorination alone is not a dedicated metals-removal step.

Common Pitfalls:

• Assuming chlorination 'cleans' all contaminants—its scope is microbiological, not universal.
• Ignoring contact time and residual maintenance for effective disinfection.

Final Answer:

Bacteria and pathogenic microorganisms