11.3 Granular Filtration

Question 1

what are the five mechanisms of filtration?

Answer 1

mechanical screening, sedimentation, flocculation, interception, impaction

Question 2

what is the dominant filtration mechanism for slow sand filters?

Answer 2

mechanical screening

Question 3

filtration mechanism - size exclusion (particles are larger than the smallest opening through which water flows)

Answer 3

mechanical screening

Question 4

filtration mechanism - the pore spaces between the grains are small and the water velocity through the interstices is also small. if the mass and diameter of the particles is large enough, it will settle through the short distance from the water to the particle

Answer 4

sedimentation

Question 5

filtration mechanism - because the streamlines of water flowing through the interstices bend as the water passes around the granular material, particles are brought into contact and flocculate and grown larger in size. the large may then be captured by straining

Answer 5

flocculation

Question 6

filtration mechanism - bending streamlines also cause smaller particles to pass near enough to the grains of filer material to be intercepted

Answer 6

interception

Question 7

filtration mechanism - the particles have sufficient mass that they cannot follow the alteration in the flow path with the streamlines, and their trajectory causes them to impact on the granular material of the filter

Answer 7

impaction

Question 8

what are the two models of fundamental filtration theory?

Answer 8

microscopic and macroscopic model

Question 9

transport and attachment model that describes accumulation of particles on a single media grain by sedimentation, interception and diffusion

Answer 9

microscopic model

Question 10

model based on mass balance and empirical rate expression to relate the duration of ripening, water quality, time to breakthrough, and time to terminal headloss. does not describe particle transport or attachment.

Answer 10

macroscopic model