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BioreactorBioreactor

Prof. S.T. YangDept. Chemical & Biomolecular Eng.

The Ohio State University

Desirable properties of Desirable properties of bioreactorsbioreactors

Simplicity of design

Continuous operation w/ narrow distribution time

Large number of organisms per unit volume

Uniform distributions of microorganisms

Simple and effective oxygen supply

Low energy requirement

Uniform distribution of energy

Bioreactor design

Types of bioreactors

Agitation and Mixing

Aeration

Immobilized cell

bioreactors

Stirred tank bioreactorStirred tank bioreactor

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AirAir--lift and bubblelift and bubble--column column bioreactors bioreactors Membrane bioreactorsMembrane bioreactors

Typical membrane bioreactors for biological wastewater treatment

Immobilized cell bioreactors

Products

Feed

Feed

Products

Immobilized cells

Products

Feed

Air Sparger

Bubble

Draft tube

Gas outlet

Stirred Tank Bioreactor

Packed Bed Bioreactor

Fluidized Bed Bioreactor

Air-lift Bioreactor

Bioreactors for cell cultureBioreactors for cell culture

Stirred tank bioreactor

Air-lift bioreactor

Packed bed bioreactor

Hollow fiber bioreactor

Rotating wall bioreactor

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Solid State Fermentation Solid State Fermentation BioreactorsBioreactors

Rotating Drum

Bed height

Fountain height

Spouted bed

Air supply

Exhaust

Water spray

Tray reactor

PlaFractor™ stacks fermenter

Photobioreactors

MicrobioreactorsMicrobioreactors Other Bioreactors?Other Bioreactors?

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Stirred Tank Bioreactor

Agitation and Mixing

Impeller design

Mixing time

Power consumption

Mass transfer coefficient

Aeration

Agitation / Mixing

Keep the cells in suspension

Increase homogeneity (pH, Temp, Conc…)

Disperse air bubbles

Increase mass transfer efficiency

Types of impellers Fluid Movement

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Flow Patterns with aeration Mixing with aeration

Geometry of a standard stirred tank fermentor

Design considerations

Agitation power consumption

Aeration determination of kla

Mass transfer correlation

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Fermentation broth rheology

Newtonian fluid:YeastBacterial culture

Non-Newtonian fluid:Mycelia growth (mold)Polymeric compounds (polysaccharides)

Examples

γ

τ

pseudoplastic

Newtonian

dilatant

Bingham plastic

Casson body

Fluid Rheology

Newtonian Viscous Flow (constant μ)

γμυμτ ⋅=∂∂

⋅−=y

τ = shear stress = F/A (g/cm2-sec2)dv/dy = velocity gradientγ = shear rateμ= viscosity (g/cm-sec)

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Non-Newtonian fluid

τ = shear stress = F/A (g/cm2-sec2)τ0 = yield stress = F/A (g/cm2-sec2)γ = shear rateκ = consistency coefficientN = flow behavior index

n)(0 γκττ +=For aerated system, the power requirement is less due to decrease in density

Non-Newtonian fluid

ηa = apparent viscosity (time dependent)

n > 1 dilatant fluidn = 1 Newtonian fluidn < 1 pseudoplastic fluid

γηγγκτ ⋅=⋅⋅= −a

n )( 1

τ0 = 0 (power-law fluid)

Non-Newtonian fluid

n = 1 τ > τ0 Bingham plastic fluid

τ0 ≠ 0

γγκγττ ⋅⋅+⋅= −− )( 110

nn

21

21

02

1γκττ ⋅+= c

Casson body fluid:

Power requirement for agitation

Newtonian fluid:Non-gassed systemGassed systemMultiple impeller fermenter

Non-Newtonian fluid:Non-gassed systemGassed system

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Agitation – Power number

Non-gassed, Newtonian fluid

53iil

no DNgPP

ρ⋅

=

Pno = power number = external force / inertial forceP = Power (g cm/sec)g = Newton’s law conversion favtor (cm/sec2)ρl = density of the fluid (g/cm3)Ni = rotational speed (sec-1)Di = impeller diameter (cm)

Agitation – Reynolds number

Non-gassed, Newtonian fluid

Rei = Reynolds number = inertial force / viscous forceρl = density of the fluid (g/cm3)Ni = rotational speed (sec-1)Di = impeller diameter (cm)μl= viscosity (g/cm-sec)

l

iili

DNμ

ρ 2

Re⋅⋅

=

Power Number vs. Re CorrelationIn the turbulent regime: Pno = constant

In the laminar flow:

The proportionality constant in each case depends on the impeller geometry (shape factor)

53iino DNP ∝

32iino DNP ∝

inoP

Re1

∝

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Simultaneous aeration & agitationFor aerated system, the power requirement is less due to decrease in density

ii

ig

ii

ga DN

DF

DN

FN

2

3 ==

Na = aeration number = superficial gas velocity ÷ impeller top velocityPa = Power requirement for aerated systemP = Power requirement for non-aerated system

Power in multiple impeller fermenter

HL

Hi

Di

Di < Hi < 2 Di

i

iL

i

iL

DDH

ND

DH −<<

− 2

Pno α N (# of impellers)

Gassed Power Consumption

Michel and Miller empirical equationValid for Newtonian and Non-Newtonian fluidIndependent of the impeller Reynolds number

45.056.0

32)(

g

iino F

DNPcP ⋅=

10

Non-Newtonian Fluidnon-gassed system

Modified Reynolds Number

In fermentation, K and n change with concentration of macromolecules and timeK = a [P]b

ln K = c + dn

nl

nii

i nn

KND

⎟⎠⎞

⎜⎝⎛

+⋅⋅⋅

=−

261.0'Re

22 ρ

Non-Newtonian Fluidgassed system

Valid for the turbulent flow region

45.056.0

32

)(g

iino F

DNPcP ⋅=