To remove a very small amount of tiny solid impurities from a liquid stream (polishing duty), which separation device is preferred?

Introduction / Context:
When solids loading is very low but high clarity is required, a polishing filter is selected to capture fine particulates without excessive footprint or complexity.

Given Data / Assumptions:

• “Very small amount” of suspended fines.
• Objective: produce a clarified liquid.
• Operating mode: practical industrial service.

Concept / Approach:
Pressure filters (e.g., cartridge, plate-and-frame operated at pressure, sparkler filters) provide high driving force and fine retention in compact housings, making them ideal for polishing duties. Vacuum filters are efficient for higher solids slurries and cake discharge, not trace removal. Centrifuges excel for immiscible liquid separation or moderate solids, but for tiny amounts of fine solids, filtration media achieve finer nominal ratings. Coagulants assist clarification but are not a separation device by themselves.

Step-by-Step Solution:
Match low-solids polishing → fine media under pressure.Select pressure filter as the most suitable unit operation.

Verification / Alternative check:
Water polishing, chemical/petrochemical side-streams, and beverages commonly use cartridge or precoat pressure filters for final clarity.

Why Other Options Are Wrong:
Vacuum filter: better for bulk cake formation, not tiny residuals.Centrifugal filter: less effective for the finest, trace solids in low-solids feeds.Coagulant: chemical aid, not a physical separator.

Common Pitfalls:
Confusing low-solids polishing with bulk dewatering applications.

Final Answer:
Pressure filter