Water treatment fundamentals: For removing suspended solids from polluted water in the most practical and economical way (prior to finer polishing), which primary unit operation is used?

Introduction / Context:
Designing a treatment train starts with the cheapest bulk separation steps. Suspended solids are best handled early by gravity clarification before moving on to filtration, biological treatment, or disinfection. Picking the right first step minimizes lifecycle cost and footprint.

Given Data / Assumptions:

• Suspended solids are the primary concern at this stage.
• We seek a practical, economical process suitable for large flows.
• Pre-treatment chemicals (coagulants) may be added to enhance settling where needed.

Concept / Approach:
Sedimentation (clarification) exploits gravity to settle denser-than-water particles in quiescent basins or clarifiers. It is simple, robust, and cost-effective. Skimming targets floatables; chlorination kills pathogens but does not remove solids; biological oxidation degrades dissolved/colloidal organics, not settleable solids; reverse osmosis is too costly for bulk solids removal.

Step-by-Step Solution:
Match contaminant type (suspended solids) to the most economical separation (settling).Confirm alternatives: skimming is for oils/greases; chlorination is for disinfection; biological oxidation is secondary treatment; RO is polishing.Select “Sedimentation (clarification)”.

Verification / Alternative check:
Standard water and wastewater flowsheets place primary clarifiers ahead of aeration basins and filters to cut loadings and operating costs.

Why Other Options Are Wrong:
Skimming: limited to floatables, not general suspended solids.Chlorination: does not remove solids; it disinfects.Biological oxidation: targets dissolved/colloidal organics; not a primary solids removal step.Reverse osmosis: excessive cost/complexity for bulk solids removal.

Common Pitfalls:
Jumping to advanced membranes when gravity settling provides a cheaper, simpler solution with fewer fouling issues.

Final Answer:
Sedimentation (clarification)