1. Desirable properties of
bioreactors
Bioreactor Simplicity of design
Continuous operation w/ narrow distribution time
Large number of organisms per unit volume
Prof. S.T. Yang Uniform distributions of microorganisms
Dept. Chemical & Biomolecular Eng. Simple and effective oxygen supply
The Ohio State University Low energy requirement
Uniform distribution of energy
Bioreactor design Stirred tank bioreactor
Types of bioreactors
Agitation and Mixing
Aeration
Immobilized cell
bioreactors
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2. Air-lift and bubble-column
bioreactors Membrane bioreactors
Typical membrane bioreactors for biological wastewater treatment
Immobilized cell bioreactors Bioreactors for cell culture
Stirred Tank Packed Bed Fluidized Bed Air-lift
Bioreactor Bioreactor Bioreactor Bioreactor
Gas outlet
Immobilized Products Products
Feed
cells
Bubble
Stirred tank bioreactor
Air-lift bioreactor
Draft tube Packed bed bioreactor
Hollow fiber bioreactor
Products Feed Feed Rotating wall bioreactor
Air Sparger
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3. Solid State Fermentation
Bioreactors Photobioreactors
Water spray
Tray reactor
Air Exhaust
supply
Fountain height
Bed height
PlaFractor™ stacks fermenter Rotating Drum Spouted bed
Microbioreactors Other Bioreactors?
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4. Stirred Tank Bioreactor Agitation / Mixing
Agitation and Mixing Keep the cells in suspension
Impeller design Increase homogeneity (pH, Temp, Conc…)
Mixing time
Disperse air bubbles
Power consumption
Increase mass transfer efficiency
Mass transfer coefficient
Aeration
Types of impellers Fluid Movement
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5. 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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6. Fermentation broth rheology Examples
Newtonian fluid:
Yeast
Bacterial culture
Non-Newtonian fluid:
Mycelia growth (mold)
Polymeric compounds (polysaccharides)
Fluid Rheology
τ Bingham plastic Newtonian Viscous Flow (constant μ)
dilatant ∂υ
Casson body τ = −μ ⋅ = μ ⋅γ
Newtonian
∂y
τ = shear stress = F/A (g/cm2-sec2)
pseudoplastic
dv/dy = velocity gradient
γ = shear rate
μ= viscosity (g/cm-sec)
γ
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7. Non-Newtonian fluid Non-Newtonian fluid
For aerated system, the power requirement is τ0 = 0 (power-law fluid)
less due to decrease in density
τ = τ 0 + κ (γ ) n τ = (κ ⋅ γ n −1 ) ⋅ γ = η a ⋅ γ
τ = shear stress = F/A (g/cm2-sec2) ηa = apparent viscosity (time dependent)
τ0 = yield stress = F/A (g/cm2-sec2)
γ = shear rate n>1 dilatant fluid
κ = consistency coefficient n=1 Newtonian fluid
N = flow behavior index n<1 pseudoplastic fluid
Power requirement for
Non-Newtonian fluid agitation
τ0 ≠ 0 Newtonian fluid:
Non-gassed system
τ = (τ 0 ⋅ γ n −1
+ κ ⋅γ n −1
) ⋅γ Gassed system
Multiple impeller fermenter
n=1 τ > τ0 Bingham plastic fluid
Non-Newtonian fluid:
Non-gassed system
1 1 1 Gassed system
Casson body fluid: τ 2
=τ0 2 + κc ⋅γ 2
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8. Agitation – Power number Agitation – Reynolds number
Non-gassed, Newtonian fluid Non-gassed, Newtonian fluid
P⋅g ρ l ⋅ N i ⋅ Di 2
Pno = Re i =
ρ l N i 3 Di 5 μl
Pno = power number = external force / inertial force Rei = Reynolds number = inertial force / viscous force
P = Power (g cm/sec) ρl = density of the fluid (g/cm3)
g = Newton’s law conversion favtor (cm/sec2) Ni = rotational speed (sec-1)
ρl = density of the fluid (g/cm3) Di = impeller diameter (cm)
Ni = rotational speed (sec-1) μl= viscosity (g/cm-sec)
Di = impeller diameter (cm)
Power Number vs. Re Correlation
In the turbulent regime: Pno = constant
Pno ∝ N i Di
3 5
1
In the laminar flow: Pno ∝
Re i
Pno ∝ N i Di
2 3
The proportionality constant in each case depends
on the impeller geometry (shape factor)
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9. Simultaneous aeration &
agitation
For aerated system, the power requirement is less due to
decrease in density
2
Fg Fg Di
Na = 3
=
N i Di N i Di
Na = aeration number = superficial gas velocity ÷ impeller top velocity
Pa = Power requirement for aerated system
P = Power requirement for non-aerated system
Power in multiple impeller
fermenter Gassed Power Consumption
Di < Hi < 2 Di Michel and Miller empirical equation
Valid for Newtonian and Non-Newtonian fluid
Independent of the impeller Reynolds number
HL H L − 2 Di H − Di
<N< L
Hi Di Di 3
P 2 N i Di
Pno = c ⋅ ( 0.56 ) 0.45
Di Pno α N (# of impellers)
Fg
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10. Non-Newtonian Fluid Non-Newtonian Fluid
non-gassed system gassed system
Modified Reynolds Number
2−n Valid for the turbulent flow region
D ⋅ Ni ⋅ ρl ⎛ n ⎞
2 n
Re i ' = i ⎜ ⎟
0.1 ⋅ K ⎝ 6n + 2 ⎠ 3
P 2 N iDi
In fermentation, K and n change with Pno = c ⋅ ( 0 . 56 ) 0 . 45
Fg
concentration of macromolecules and time
K = a [P]b
ln K = c + dn
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