Identify the common filter aid used to build a porous precoat and prevent medium blinding during clarification.

Introduction / Context:
Filter aids are inert, porous materials used either as a precoat or as a body feed to maintain permeability and avoid rapid pressure buildup in fine-solid filtrations.

Given Data / Assumptions:

• Looking for the standard, widely used aid for precoat filtration.
• Applications include beverages, pharmaceuticals, and chemicals.

Concept / Approach:
Diatomaceous earth (kieselguhr) consists of fossilized diatom frustules with high porosity and complex microstructure, giving excellent permeability and fine particle capture. Canvas is a medium, not an aid; calcined lime is a reagent/filler and not a structural filter aid.

Step-by-Step Solution:
Match “filter aid” definition to inert porous solids.Select diatomaceous earth as the standard choice.

Verification / Alternative check:
Industry practice commonly references kieselguhr and perlite as primary aids; DE is the most common.

Why Other Options Are Wrong:
Canvas: medium support cloth, not an aid.Calcined lime: chemistry additive, not a precoat material.

Common Pitfalls:
Confusing the filter medium with filter aid.

Final Answer:
Diatomaceous earth