Municipal water treatment — The standard process train (in the correct order) is based upon which sequence?

Introduction / Context:
Conventional municipal water treatment follows an ordered set of unit processes to remove turbidity, pathogens, and taste/odor compounds. Knowing the correct sequence is crucial for understanding why each step works and how overall pathogen barriers are layered for public health protection.

Given Data / Assumptions:

• We refer to the essential backbone of conventional plants (coagulation/flocculation and sedimentation), followed by filtration, and finally disinfection.
• Sedimentation is commonly paired with coagulation/flocculation but may be omitted in simplified listings.
• Final disinfection is typically chlorine-based (or alternatives like ozone/UV) after filtration.

Concept / Approach:
Coagulation destabilizes colloids; flocculation aggregates particles into settleable flocs; sedimentation removes most solids; filtration polishes remaining turbidity and microbes; disinfection inactivates pathogens that pass filters and provides residual protection in the distribution system. Thus, coagulation must precede filtration, and disinfection is last in the train.

Step-by-Step Solution:

Verification / Alternative check:
Design manuals depict the order: Coagulation/Flocculation → Sedimentation → Filtration → Disinfection. Option (a) correctly preserves the relative order among the listed steps.

Why Other Options Are Wrong:

• Chlorination before filtration: wastes disinfectant and forms excess by-products.
• Filtration before coagulation: filters clog rapidly; turbidity removal is poor.
• Chlorination before filtration in (d): misordered and operationally inefficient.

Common Pitfalls:
Forgetting the sedimentation step (often implicit) and misplacing disinfection upstream; primary disinfection almost always comes last.

Final Answer:
Coagulation → Filtration → Chlorination (disinfection)