WTO Sedimentation and Filtration 3

Question 1

What is the typical surface overflow rate range for a conventional sedimentation basin treating surface water?

Accepted Answer

500–1,000 gpd/ft²

Answer

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

Question 2

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

Accepted Answer

Break up mud balls and improve media cleaning

Answer

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

Question 3

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

Accepted Answer

The square of the particle diameter

Answer

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

Question 4

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

Accepted Answer

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

Answer

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

Question 5

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

Accepted Answer

10% of the sand by weight is finer

Answer

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.

(WTO) Water Treatment Operator Certification Practice Test

(WTO) Water Treatment Operator Certification Practice Test

WTO Sedimentation and Filtration 3