WTO - Water Treatment Operator Sedimentation and Filtration Questions and Answers

Question 1

Which of the following principles primarily governs the process of sedimentation in a water treatment clarifier?

Accepted Answer

Gravity

Answer

Sedimentation is a physical water treatment process that uses gravity to remove suspended solids from water. In the relatively still water of a clarifier or settling basin, particles heavier than water will settle to the bottom due to the force of gravity.

Question 2

A water treatment plant is treating raw water with low turbidity and high quality. To reduce capital and operational costs, which treatment scheme would be most appropriate?

Accepted Answer

Direct Filtration

Answer

Direct filtration is a suitable treatment method for high-quality source waters with low turbidity. This process omits the sedimentation step that is part of conventional filtration, thereby saving space and reducing costs. Coagulation, flocculation, and filtration are still utilized.

Question 3

An operator observes a rapid increase in head loss across a gravity filter, and the finished water turbidity is approaching the regulatory limit. What is the most immediate and appropriate action to take?

Accepted Answer

Initiate a backwash cycle.

Answer

A rapid increase in head loss (differential pressure) and turbidity breakthrough are key indicators that a filter is clogged with accumulated particles and needs to be cleaned. Initiating a backwash cycle is the standard procedure to clean the filter media by reversing the flow of water and flushing out the trapped solids.

Question 4

According to Stokes' Law, which characteristic of a suspended particle will result in the fastest settling velocity in a sedimentation basin?

Accepted Answer

High density and large diameter

Answer

Stokes' Law describes the settling of particles in a fluid. The settling rate is directly proportional to the particle's density and the square of its diameter. Therefore, particles that are larger and denser will settle out of the water much faster than smaller, less dense particles.

Question 5

During a filter backwash, what is the primary purpose of the initial air scour phase?

Accepted Answer

To break up the compacted filter bed and loosen trapped particles.

Answer

The air scour step in a backwash procedure involves pushing compressed air up through the filter. This action causes the filter bed to expand and agitates the media, effectively breaking up the compacted layer of solids (the filter cake) and loosening the particles that have been trapped within the media, preparing them to be washed away by the water phase of the backwash.

(WTO) Water Treatment Operator Certification Practice Test

(WTO) Water Treatment Operator Certification Practice Test

WTO - Water Treatment Operator Sedimentation and Filtration Questions and Answers