Diatomaceous earth filtration maximum turbidity value?

• A. 5 ntu
• B. 10 ntu
• C. 20 ntu
• D. 40 ntu

Answer: (B)

Diatomaceous earth filtration relies on a fine precoat that traps tiny particles, so there’s a practical limit to how turbid the water can be fed to the filter. The maximum influent turbidity for DE filtration is 10 NTU, a value chosen because the DE layer can handle that level of suspended solids without clogging too quickly or reducing filtration efficiency. If the incoming water is more turbid than that, pre-treatment steps like coagulation and clarification are typically needed before filtration to reduce turbidity, or a different filtration approach should be used. While the filtrate itself should be very clear (often below 0.3 NTU with proper operation), the key point here is ensuring the DE filter isn’t overwhelmed by incoming turbidity.