Subject Name: Bioseparation Technology
Unit No: 2 Unit Name: Solid Liquid
Separation
Faculty Name : Dr. Madhavi Vernekar
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Bioseparation Technology
Unit 2: Solid Liquid Separation
(Font: Source sans pro, Size: 32)
Faculty Name : Dr. Madhavi Vernekar
(Font: Source sans pro, Size: 20)
Unit No: 1 Unit name:....................................... (Separator Page for every
section)
Lecture No:
Sub Topic Name:
Sedimentation
Sedimentation
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When a solid particle moves through a viscous medium under the influence of
gravity, it will attain a constant falling velocity after a certain time. This
phenomenon is called Sedimentation
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A tube of anticoagulated whole blood left standing on a bench top will eventually
separate into plasma, red blood cell and white blood cell fractions.
However, the length of time required precludes this manner of separation for
most applications.
•
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Gravity sedimentation commonly used in biological waste water treatment.
Factors influencing Sedimentation
1. Gravitational Force
2. Buoyancy force
3. Drag force
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•
Consider a tank containing highly diluted suspension of spherical particles
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Because of Earth’s pull of gravity the particles start to move downwards
Forces acting on particle during sedimentation
1. Gravitational Force
2. Buoyancy force
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dp particle diameter (m)
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s solid density (Kg/m3)
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g = acceleration due to gravity (m/s2)
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l liquid density (Kg/m3)
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= Dynamic Viscosity Pa.s
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Vg= Gravitational Sedimentation rate (m/s)
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3. Drag force
The buoyancy and drag force will be counterbalanced by the gravitational force
Fg= Fd+Fb ……or we can write
Fd= Fg-Fb
Substituting Eqn 1,2 and 3
3dpVg= /6dp3 s g- /6dp3 l g
Stokes Law
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Stokes Law
Sedimentation Rate Vg is determined by
the physical characteristics of the particles (diameter of particle and its density)
and the medium properties (viscosity of the liquid and the density of the liquid).
Sedimentation rate depends on
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Diameter of the particle dp…….. dp increases
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Density differences (s - l) increases
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Viscosity  decreases
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Vg increases
Vg increases
Vg increases
Advantages of Sedimentation
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Can be used only for larger particles
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Commonly used in waste water treatment.
Disadvantages of Sedimentation
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Slow process
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Requires large equipment
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Residence time unacceptably long
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