Water treatment selection: Which process is specifically adopted to remove very fine suspended particles that are not effectively settled by plain sedimentation?

Introduction / Context:
Public water treatment trains use a sequence of unit processes that progressively remove contaminants: screening for coarse debris, coagulation–flocculation, sedimentation for settleable solids, and filtration for fine suspended matter that escapes settling. Correctly matching the process to the target particle size is critical for plant performance.

Given Data / Assumptions:

• Very fine suspended particles are present after sedimentation.
• No specialized membrane systems are considered; focus is on conventional rapid sand filtration or slow sand filtration.

Concept / Approach:
Filtration passes water through granular media (sand, anthracite) where mechanisms such as straining, interception, and adsorption remove remaining turbidity. Microflocs generated by coagulation are captured effectively, producing low-turbidity, pathogen-reduced effluent suitable for disinfection.

Step-by-Step Solution:
Discard screening: targets large debris only.Acknowledge sedimentation: removes heavier particles but leaves fine colloids.Identify filtration: designed for fine suspended removal following coagulation.Confirm that filtration is the standard step before final disinfection.

Verification / Alternative check:
Plant performance data show significant turbidity reduction across filters even when clarifier effluent turbidity is modest (e.g., 2–5 NTU). Filtration achieves finished water turbidities often < 0.3–1 NTU under optimized conditions.

Why Other Options Are Wrong:

• Screening: removes rags and sticks; ineffective for fines.
• Sedimentation: not sufficient for stable colloids.
• Boiling: a household-scale disinfection method; not a turbidity removal step.
• Solar distillation: not a conventional municipal process for turbidity control.

Common Pitfalls:

• Assuming disinfection replaces filtration; disinfectants are less effective in turbid water.
• Skipping coagulation leads to filter breakthrough and short runs.

Final Answer:
filtration