WTO Sedimentation and Filtration 5

Question 1

What is 'filter-to-waste' and when is it typically employed?

Accepted Answer

Routing initial filter effluent to waste until turbidity meets standards after backwash

Answer

Filter-to-waste routes the first portion of filtrate (during the ripening period after backwash) to waste rather than the clearwell, preventing poor-quality water from entering distribution.

Question 2

Slow sand filtration differs from rapid sand filtration primarily because slow sand relies on:

Accepted Answer

A biologically active layer called the schmutzdecke for removal

Answer

Slow sand filters develop a biologically active layer (schmutzdecke) on the surface that physically strains particles and biologically degrades organics, requiring no coagulation pretreatment.

Question 3

What does a rising head loss curve that suddenly flattens during a filter run most likely indicate?

Accepted Answer

A broken underdrain lateral allowing short-circuit flow

Answer

A sudden flattening of a rising head loss curve can indicate a broken underdrain or lateral, which creates a short-circuit path that bypasses the clogged media and artificially reduces measured head loss.

Question 4

Which backwash strategy introduces air at a low rate before water to improve media cleaning?

Accepted Answer

Air scour followed by water backwash

Answer

Air scour followed by water backwash first introduces air to aggressively scrub the media grains, then uses water alone to flush detached solids out of the filter.

Question 5

In pressure filtration systems, an advantage over gravity filtration is:

Accepted Answer

Ability to operate at higher hydraulic loading rates without head loss concerns

Answer

Pressure filters use pressurized vessels that overcome head loss without relying on gravity head alone, allowing higher flow rates that would cause unacceptable head loss in an open gravity filter.

(WTO) Water Treatment Operator Certification Practice Test

(WTO) Water Treatment Operator Certification Practice Test

WTO Sedimentation and Filtration 5