Practice Test Geeks(WTO) Water Treatment Operator Certification Practice Test
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Sedimentation and Filtration Flashcards

7 cards from real WTO 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 typical surface overflow rate range for a conventional sedimentation basin treating surface water?

    Answer: 500–1,000 gpd/ft²

    Conventional sedimentation basins treating surface water are typically designed for surface overflow rates of 500–1,000 gpd/ft² to achieve adequate particle removal.

  2. During filter backwash, auxiliary surface wash or air scour is used to:

    Answer: Break up mud balls and improve media cleaning

    Auxiliary surface wash or air scour agitates the media to break apart compacted mud balls and organic deposits that backwash water alone cannot dislodge.

  3. Stokes' Law predicts that settling velocity of a spherical particle is proportional to:

    Answer: The square of the particle diameter

    Stokes' Law states that settling velocity is proportional to the square of the particle diameter (d²), so doubling diameter increases settling velocity fourfold.

  4. A filter run that produces an initial turbidity spike immediately after startup is best addressed by:

    Answer: Using a filter-to-waste period before placing the filter online

    A filter-to-waste period diverts initial poor-quality filtrate to waste until the filter ripens and produces acceptable turbidity.

  5. The effective size (ES) of filter sand is defined as the grain diameter at which:

    Answer: 10% of the sand by weight is finer

    Effective size (ES) is the d10 value — the sieve size that passes 10% of the sand by weight — and controls the initial head loss in a clean filter.

  6. What type of sedimentation basin uses a rotating rake mechanism to collect settled sludge at a central drain?

    Answer: Circular clarifier

    Circular clarifiers use rotating rake or scraper mechanisms that continuously move settled sludge from the basin floor to a central hopper for withdrawal.

  7. Which filter media characteristic is described by the uniformity coefficient (UC)?

    Answer: The ratio of d60 to d10, describing the range of grain sizes

    The uniformity coefficient (UC = d60/d10) quantifies the spread of grain sizes; a lower UC (closer to 1.0) indicates more uniformly sized media.