Downstream processing (solid-liquid separation)

Question 1

Five stages in downstream processing after Fermentation:

Answer 1

1. Solid-Liquid Separation
2. Release of Intracellular Products
3. Concentration
4. Purification by Chromatography and
5. Formulation

Question 2

What is solid-liquid separation?

Answer 2

The first step in product recovery is the separation of whole cells (cell biomass) and other insoluble ingredients from the culture broth (Note: If the desired product is an intracellular metabolite, it must be released from the cells before subjecting to solid-liquid separation).
Some authors use the term harvesting of microbial cells for the separation of cells from the culture medium

Question 3

Several methods are in used for solid-liquid separation, these are:

Answer 3

1. Flotation
2. Flocculation
3. Filtration
4. Centrifugation

Question 4

For flotation. the presence of certain substances, referred to as ______________
, facilitates stable foam formation e.g., long chain fatty acids, amines.

Answer 4

collector substances

Question 5

What are some flocculating agents?

Answer 5

inorganic salt, organic polyelectrolyte, mineral
hydrocolloid

Question 6

What does the process of flocculation depend on?

Answer 6

The process of flocculation depends on the nature of cells and the ionic constituents of the medium.

Question 7

What is flocculation?

Answer 7

In flocculation, the cells (or cell debris) form large aggregates to settle down for easy removal.

Question 8

What factors does efficiency of filtration depend on?

Answer 8

the size of the organism,
presence of other organisms,
viscosity of the medium,
and temperature.

Question 9

What types of filters are there?

Answer 9

1. Depth filters
2. Absolute filters
3. Rotary Drum Vacuum Filters
4. Membrane filters

Question 10

What are depth filters composed of?

Answer 10

They are composed of a filamentous matrix such as glass wool, asbestos or filter paper.

Question 11

What are absolute filters?

Answer 11

These filters are with specific pore sizes that are smaller than the particles to be removed.
Bacteria from culture medium can be removed by absolute filters.

Question 12

Rotary drum vacuum filters have been successfully used
for filtration of _______________ and ________________.

Answer 12

yeast cells and filamentous fungi

Question 13

What are rotary drum vacuum filters used for?

Answer 13

These filters are frequently used for separation of broth containing 10-40% solids (by volume) and particles in the size of 0.5-10μm.

Question 14

What are some of the advantages of rotary drum vacuum filters?

Answer 14

The equipment is simple with low power
consumption and is easy to operate.

Question 15

Name the two types of membrane filtrations

Answer 15

1. static filtration
2. cross-flow filtration

Question 16

What is the major limitation of membrane filtration?

Answer 16

clogging of filters is a major limitation

Question 17

What is the advantage of cross-flow filtration over static filtration?

Answer 17

the culture broth is pumped in a crosswise fashion across the membrane. This reduces the clogging process

Question 18

What are the 3 major types of filtrations based on particle sizes and other characters?

Answer 18

1. Microfiltration
2. Ultrafiltration
3. Reverse Osmosis

Question 19

What can be removed using depth filters?

Answer 19

Filamentous fungi

Question 20

What can be removed using absolute filters?

Answer 20

Bacteria from culture medium can be removed by absolute filters

Question 21

State the size of particles separated by each type of filtration

Answer 21

1. Microfiltration 0.1- 10um
2. Ultrafiltration 0.001-0.1um
3. Reverse Osmosis 0.0001-0.001um

Question 22

State the size of particles separated by each type of filtration

Answer 22

1. Microfiltration 0.1- 10um
2. Ultrafiltration 0.001-0.1um
3. Reverse Osmosis 0.0001-0.001um

Question 23

State the compound separated by microfiltration

Answer 23

Cells/cell factions
Viruses

Question 24

State the compound separated by ultrafiltration

Answer 24

Compounds with MW greater than 1000 (eg enzymes)

Question 25

State the compound separated by reverse osmosis (hyperfiltration)

Answer 25

Compounds with MW less than 1000 (eg lactose)

Question 26

What is the technique of centrifugation based on?

Answer 26

Principle of density differences between to be separated and medium.

Question 27

What kind of centrifuges have been developed for large scale industrial centrifugation?

Answer 27

Continuos flow industrial centrifuges