L3: Filtration

Question 1

What are filter aids, and why are they added to the feed in conventional filtration?

Answer 1

Filter aids are powdered solids added to the feed to keep filter pores open, prevent filter cake compression, and increase filtration speed by allowing liquid to flow more freely.

Question 2

Describe the composition and purpose of diatomaceous earth in filtration.

Answer 2

Diatomaceous earth, made of silica from algae skeletons, has high permeability and is resistant to strong acids and bases, making it ideal for use as a filter aid.

Question 3

What is the role of perlite in conventional filtration, and what makes it suitable for high-flow applications?

Answer 3

Perlite, a porous volcanic material, expands when heated, creating high porosity. It is ideal for high-flow applications where clarity is less critical than speed.

Question 4

Explain the batch filtration method using a plate-and-frame setup.

Answer 4

In plate-and-frame filtration, feed enters pressurized chambers that contain alternating filter plates and frames. The liquid passes through a filter medium, while solids are retained, forming a cake in each chamber.

Question 5

Describe the continuous rotary vacuum filter process and identify one advantage and one disadvantage of using this method.

Answer 5

The rotary vacuum filter continuously rotates through a slurry, applying vacuum pressure to draw liquid through the filter medium while solids form on the drum’s surface.

Advantage: Operates continuously over long periods.

Disadvantage: Disposal of used filter aid mixed with biomass can be costly due to environmental regulations.

Question 6

What are the key differences between membranes and conventional filters?

Answer 6

Membranes operate based on specific pore size and molecular diffusion, allowing selective separation of solutes, while conventional filters rely more on pore size alone and lack selectivity at the molecular level.

Question 7

List three benefits of using membrane operations for separation in bioprocesses.

Answer 7

1. Continuous operation capability.
2. Low energy consumption.
3. Ability to operate under mild, non-destructive conditions.

Question 8

What are some drawbacks of membrane filtration, especially concerning fouling?

Answer 8

1. Membrane fouling from particle buildup, reducing efficiency.
2. Limited membrane lifespan due to fouling and wear.
3. Low selectivity or flux in some configurations.

Question 9

What are the typical applications of membrane filtration in downstream processing (DSP)?

Answer 9

Membranes are used for concentration, purification, and fractionation of products in DSP, as well as for removing unwanted small molecules or concentrating target molecules.

Question 10

Explain the function of a spiral-wound membrane module and where it is commonly used.

Answer 10

A spiral-wound module arranges the membrane in a spiral configuration around a central core, maximizing membrane area in a compact design. It is commonly used in applications like reverse osmosis and ultrafiltration.

Question 11

What are hollow fiber membrane modules, and why are they beneficial in high-pressure applications?

Answer 11

Hollow fiber modules contain tightly packed fibers with small diameters that can withstand high pressure, providing a large membrane surface area suitable for high-pressure separations.

Question 12

Compare plate-and-frame and tubular membrane modules in terms of cost and fouling resistance.

Answer 12

Plate-and-frame: More expensive and primarily suited for smaller applications but offers easy maintenance.

Tubular: Resistant to fouling and generally used in ultrafiltration but also costly.

Question 13

What is concentration polarization, and how does it affect permeate flux over time?

Answer 13

What is concentration polarization, and how does it affect permeate flux over time?

Question 14

List at least three mechanisms that contribute to fouling in membrane filtration.

Answer 14

• Pore-blocking: Solids clog pores, reducing permeability.
• Adsorption: Molecules adhere to the membrane surface.
• Gel layer formation: Solutes form a gel layer, obstructing flow.

Question 15

What are external and internal fouling, and how do they differ in membrane operations?

Answer 15

• External fouling: Occurs on the membrane surface, caused by particles or macromolecules.
• Internal fouling: Occurs within the membrane’s pores, often more challenging to remove.

Question 16

Describe one strategy for reducing fouling in membrane filtration.

Answer 16

Using periodic backwashing to flush particles off the membrane surface can reduce fouling and restore flux.

Question 17

What is the threshold flux in the context of membrane filtration, and how does it relate to fouling?

Answer 17

Threshold flux is the maximum flux below which fouling is minimal; operating above it can lead to rapid fouling due to increased concentration polarization.

Question 18

How is the resistance to mass transfer due to fouling represented mathematically in membrane processes?

Answer 18

It is often modeled by adding a fouling resistance term to the overall resistance in flux equations, which accounts for additional pressure required to overcome fouling.

Question 19

What are some strategies to optimize membrane lifetime despite common fouling issues?

Answer 19

Regular cleaning cycles, optimized process conditions, and selection of fouling-resistant membranes all help extend membrane life.

Question 20

When selecting a filtration method for a bioprocess, what factors might lead to the choice of rotary vacuum filtration over membrane filtration?

Answer 20

Rotary vacuum filtration is chosen for processes needing continuous filtration of large, particulate-rich feeds, where membrane fouling would be problematic.

Question 21

Describe the general purpose of using filtration in the early stages of DSP for extracellular products.

Answer 21

Filtration removes cells and other particulate matter, preparing the product solution for subsequent purification stages.

Question 22

Why is continuous filtration preferred for large-scale bioprocesses, and what are some challenges associated with this choice?

Answer 22

Continuous filtration supports high throughput and efficiency but faces challenges like fouling, complex maintenance, and disposal of filter aids.

Question 23

Explain the importance of selecting the right pore size in membrane filtration.

Answer 23

Correct pore size ensures selective retention or passage of target molecules, maximizing efficiency and product purity.

Question 24

What is the significance of membrane material in separation processes, particularly in harsh chemical environments?

Answer 24

Durable membrane materials resist degradation, ensuring consistent performance in harsh conditions, such as extreme pH or temperature.

Question 25

In which applications would plate-and-frame membrane modules be ideal, considering their limitations?

Answer 25

Plate-and-frame modules are suitable for small-scale or high-value applications with fouling-resistant feeds where easy maintenance is needed.

Question 26

What unique feature does the hollow fiber module provide that enhances membrane surface area?

Answer 26

Its densely packed fibers offer a high surface area within a small footprint, allowing for efficient processing in compact modules.

Question 27

How does concentration polarization impact the efficiency of membrane modules in protein separation?

Answer 27

It creates a high-concentration layer near the membrane, reducing flux and efficiency by increasing the osmotic pressure gradient

Question 28

Outline the general downstream recovery process for succinic acid (SA).

Answer 28

The SA recovery process typically involves removing cells, concentrating the product, and purifying it through filtration and membrane operations.

Question 29

Why might membrane filtration be chosen over conventional filtration in the recovery of succinic acid?

Answer 29

Membrane filtration offers a more selective separation with lower energy costs and the ability to handle smaller solutes, which is often advantageous for SA.

Question 30

What are the potential benefits of hybrid processing using both membrane and conventional filtration in SA recovery?

Answer 30

Hybrid processing combines high-capacity initial filtration with selective membrane filtration, balancing speed with high product purity.