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Filtration Media & Technologies Flashcards

7 cards from real CWS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the recommended maximum service flow rate for a greensand filter treating iron-bearing water?

    Answer: 3–5 gpm/ft²

    Greensand filters are typically rated for 3–5 gpm per square foot of bed area to allow adequate contact time for iron oxidation and filtration.

  2. In a pressure vessel filter, the term 'differential pressure' refers to:

    Answer: The pressure drop across the filter media from inlet to outlet

    Differential pressure (ΔP) is the pressure drop across the filter bed from influent to effluent, and rising ΔP indicates media loading and signals backwash need.

  3. Manganese greensand regeneration in the continuous regeneration (CR) mode uses which oxidant?

    Answer: Potassium permanganate

    In continuous regeneration mode, potassium permanganate (KMnO₄) is added to the influent to continuously re-oxidize the greensand coating as it removes manganese.

  4. Which media type would be MOST appropriate for a filter designed to target arsenic removal?

    Answer: Iron-based adsorptive media (GFH or similar)

    Granular ferric hydroxide (GFH) and similar iron-based adsorptive media are highly effective for arsenic adsorption, particularly As(V), due to strong ligand exchange with iron hydroxide sites.

  5. What is the purpose of a support gravel bed beneath filter media in a pressure filter?

    Answer: To provide even distribution and prevent media from entering the underdrain

    Graded gravel underbedding supports the filter media, prevents fines from escaping into the underdrain, and promotes even backwash flow distribution across the entire bed.

  6. A slow sand filter differs from a rapid sand filter primarily in that it:

    Answer: Operates at lower flow rates and relies on a biological schmutzdecke layer

    Slow sand filters operate at very low flow rates (0.04–0.1 gpm/ft²) and depend on the schmutzdecke, a biological layer on the sand surface, for pathogen and particle removal.

  7. During backwash of a sand filter, what percentage of bed expansion is generally targeted?

    Answer: 30–50%

    A bed expansion of 30–50% during backwash is standard, providing enough turbulence to dislodge trapped particles without washing media out of the vessel.