Filtration

Question 1

What are the fundamental aspects of filtration theory? For rapid filtration (4)

Answer 1

Straining is not an important removal mechanism
Particles adhere to media grains and are removed
Each grain is a collector
Water must be pretreated to stabilise negatively charged particles

Question 2

Assumptions of filtration model? (4)

Answer 2

Spherical particles and media
Effects of angular media on hydrodynamics are ignored
Lamda is constant with time
Constant porosity and grain dimension with time

Question 3

What are the models of n? (3)

Answer 3

Interception - dp^2
Gravity - dp^2
Diffusion -1/(dp^(2/3)

Question 4

Crossflow microfiltration?

Answer 4

In CFMF the suspension is pumped tangentially over the filtration medium. After an initial rapid increase in cake thickness, cake growth ceases and cake thickness becomes limited to some SS value. The permeate flux also levels off

Question 5

Mechanisms of transport in microfiltration? Explanation + (5)

Answer 5

Dominant mechanisms of transport in MF are hydrodynamic floe of solvent and hindered diffusion of solutes and suspended particles. Pore size is of utmost important but these also affect particle transport through membrane:

• Direct interception
• Zeta potential
• Inertial Impaction
• Adsorptive retention
• Bridging

Question 6

What is membrane plugging?

Answer 6

As MF proceeds, the formation of a cake or gel layer on the membrane surface may take place. Such a layer offers substantial resistance to flow, having a sieving capability. It is known as a dynamic membrane.

Question 7

What are the 3 resistances in MF membranes?

Answer 7

Membrane
Pore blocking
Cake

Question 8

Two types of MF membranes?

Answer 8

Tortous pore and capillary pore