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Lecture 1 bioreactor

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Lecture 1 bioreactor

  1. 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 1
  2. 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 2
  3. 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? 3
  4. 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 4
  5. 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 5
  6. 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 6
  7. 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 7
  8. 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) 8
  9. 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 9
  10. 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 10

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