6

Question 1

Clarification methods

Answer 1

1) Sedimentation
2) Centrifugation
3) Filtration

Question 2

Solid-Liquid filtration

Answer 2

• production of proteins involves cultivation of cells or microorganisms in bioreactor
• cells multiply in a growth medium, producing required proteins
• after growth process, proteins need to be purified by separating them from the surrounding liquor that contains the leftover cells and nutrients
• usually done by centrifugation as the first step

Question 3

Bioseparation

Answer 3

• Concentrate and purify products or cells after fermentation
  
  • downstream process
• Involves physical modification of the broth material rather than chemical or biochemical transformation
  
  • preserve product integrity

Question 4

Clarification - solid-liquid separation

Answer 4

If desired product is cell, the separation of solids from the liquid is a major step in product recovery.

Question 5

Challenges of solid/liquid separation

Answer 5

1) High viscosity
2) Low concentration of particulate suspension
3) Compressible solids
4) Solids with small density difference from liquid

Question 6

Sedimentation and flocculation

Answer 6

• Separation of solid from a liquid by gravitational force and differences in densities and sizes.
• Suitable for large cell aggregates in culture mediums
• Slowest but most gentle separation method

Question 7

Flocculation

Answer 7

• coagulation of smaller particles to larger agglomerates to increase particle size
• applicable to sedimentation, centrifugation and filtration
• flocculation agents include simple electrolytes and polyelectrolytes

Question 8

Centrifugation

Answer 8

• used to separate materials of different densities with the use of a force greater than gravity
• capable of separating particles of size greater than 0.1um from liquid

Question 9

Physical properties that affect centrifugation

Answer 9

1) Particle size
2) Density differences between solid and liquid
3) Viscosity of liquid
4) Angular velocity of the centrifuge

Question 10

Applications of centrifugation

Answer 10

1) recovery or removal of microoragnisms
2) separation of proteins, enzymes, nucleic acids, viruses and cellular subcomponents
3) clarification, concentration

Question 11

Filtration

Answer 11

• conventional filtration separates solids from a solid-liquid mixture by forcing liquid through a porous filter that retains solids
• solids deposited on the filter and liquid passes through
• Used for clarification, separation of cells and cell debris from broth, recovery of precipitated products and sterilisation.

Question 12

Types of filters

Answer 12

• Different types of filter media with different pore sizes
• Filters with smaller pore sizes can be used to remove extremely minute solid particles such as proteins and viruses
• More than one filter can be used, increasing filtration efficiency

Question 13

Dead-End filtration

Answer 13

• conventional filtration is also known as dead-end filtration
• cells and other solids are separated from the liquid broth with pressure or vacuum
• carried in a filter or filter press
• particle size removed range from 0.2um to several um

Question 14

Depth filters

Answer 14

• commonly used in dead-end filtration
• do not have precise pore size or structure
• larger particles will permeate through the filter

Question 15

How depth filters work

Answer 15

• made of fibrous materials with larger pores to remove larger particles
• follows the laws of chance as they are constructed by progressive deposition of fibres; fibre placements take place randomly
• stacking of fibres make it thicker than membrane filters

Question 16

Particles when going through depth filters

Answer 16

• components that are larger than the apertures of the filter will be trapped on the surface of the filter
• in the case of smaller particles, random entrapment and adsorption of matter occurs within the structure of the media
• depth filters have a random matrix or structure that creates a tortuous path through the filter

Question 17

Particles going through depth filter II

Answer 17

• depth filters may also have an electric charge that aids in the entrapment of the smaller particles
• mats of larger pore size distribution and classified by a normal retention rating

Question 18

How are depth filters specified?

Answer 18

Nominal filter retention (efficiency) is the particle size that is retained at a given percentage of efficiency (often expressed at 98%).

Question 19

Advantages of depth filters

Answer 19

• The thicker construction and higher porosity of depth filters have led to higher flow rate and dirt-loading capacity, as compared to screen and membrane filters
• Cheaper than screen and membrane filters
• manufactured from fibrous materials and woven and nonwoven polymeric material or inorganic materials