11.7 Granular Filtration

Question 1

each degree increase in water temperature requires about a __________% increase in the wash rate to prevent a reduction in the _________ _________

Answer 1

2%, bed expansion

Question 2

the limiting factor in choosing a backwash rate is the ________ _________ ________ of the smallest medium grains that are to be retained in the filter

Answer 2

terminal settling velocity

Question 3

another design criterion that is often used s to make sure that the largest diameter particles are ___________

Answer 3

fluidized

Question 4

in a dual media filter, the ________ of the anthracite is considered the largest-diameter particle

Answer 4

D90

Question 5

fluidizing the largest particle during backwash ensures it will not ____________ to the bottom of the filter

Answer 5

sink

Question 6

two alternatives for backwashing

Answer 6

water-only backwash with surface wash, water and air backwash

Question 7

what are the two types of surface water systems?

Answer 7

fixed grid and rotating arms

Question 8

how do air scour systems supply air?

Answer 8

underdrain system

Question 9

air scour systems require careful operation to avoid losing _______ medium and potential movement of the __________ support medium

Answer 9

filter, gravel