Filtration aids: what is the primary benefit of adding a filter aid to a slurry before or during filtration?

Introduction / Context:
Filter aids (e.g., diatomite, perlite, cellulose fibers) are added to problematic slurries to improve filtrability when cakes are slimy, compressible, or blinding occurs. They can be precoated onto the medium or dosed into the slurry.

Given Data / Assumptions:

• Conventional pressure or vacuum filtration of aqueous slurries.
• Filter aid used as precoat or body feed.

Concept / Approach:
Filter aids create a highly permeable, porous initial layer that supports subsequent cake, increasing permeability and reducing specific cake resistance. The net effect is a higher filtration rate at a given pressure drop. While they can mitigate blinding, claims that they always reduce pressure or always “deplug” are too general.

Step-by-Step Solution:
Add porous inert solids → composite cake with higher voidage and permeability.From Darcy’s law, increased permeability raises volumetric filtration rate at fixed ΔP and viscosity.Hence the principal benefit is faster filtration.

Verification / Alternative check:
Precoat filtration practices in beverage and chemical industries document higher rates and longer cycles when using appropriate filter aids.

Why Other Options Are Wrong:
(a) Reduction in required pressure is not universal; many operations run at fixed ΔP.(c) Deplugging is conditional; not guaranteed for all foulants or operating errors.(d) Cake porosity improves but is not guaranteed “high” for every dense particulate system.

Common Pitfalls:
Overdosing aids (increasing solids load and cost); choosing chemically incompatible aids that contaminate product.

Final Answer:
Accelerating the rate of filtration