Characteristics of ideal filter sand for water treatment: Which set of properties best describes the desired qualities of sand used in rapid or slow sand filters?

Introduction / Context:
Filter media quality directly influences run length, headloss development, and effluent turbidity in water treatment plants. Standard specifications describe mineral composition, effective size, uniformity coefficient, and cleanliness for filter sands (and anthracite where dual-media filters are used).

Given Data / Assumptions:

• Media is silica sand free of organic coatings and clay fines.
• Effective size and uniformity coefficient meet design targets (e.g., d10 and UC).
• Mechanical strength is adequate to withstand backwashing.

Concept / Approach:
Cleanliness prevents mudball formation and clogging. Uniform grading ensures predictable headloss and depth-wise particle capture. Hardness and angularity promote durability and better straining/adsorption without excessive breakdown that would generate fines and degrade performance.

Step-by-Step Solution:
Select clean silica sand with negligible organic/clay content.Specify effective size and uniformity for the filter type (slow vs rapid sand).Ensure hardness and attrition resistance for repeated backwash cycles.

Verification / Alternative check:
Factory certificates and on-site sieve analyses confirm grading; acid-solubility and turbidity tests confirm cleanliness; pilot runs validate headloss growth and effluent clarity.

Why Other Options Are Wrong:
Each single property is necessary but not sufficient; high-performing filter media must satisfy all three to ensure stable operations and long media life.

Common Pitfalls:

• Accepting broad gradations that raise headloss or reduce capture efficiency.
• Overlooking media attrition leading to fine carryover post-backwash.

Final Answer:
all the above