Bioreactor System ERT 314. Sidang /2011

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1 Bioreactor System ERT 314 Sidang /2011

2 Chapter 2:Types of Bioreactors Week 2

3 Choosing the Cultivation Method The Choice of Bioreactor Affects Many Aspects of Bioprocessing. Product concentration and purity Degree of substrate conversion Yields of cells and products Capitol cost in a process (>50% total capital expenses) Further Considerations in Choosing a Bioreactor. Biocatalyst. (immobilized or suspended) Separations and purification processes

4 Batch vs. Continuous Culture In batch culture, the culture environment continuously changes Growth, product formation, and substrate utilization all terminate after a certain time interval In continuous culture, fresh nutrient medium is continually supplied to a well-mixed culture, and products and cells are simultaneously withdrawn Growth and product formation can be maintained for prolonged periods of time At steady state, cell, product, and substrate concentrations remain constant

5 Batch or Continuous Culture? These choices represent extremes in bioreactor choices Productivity for cell mass or growth-associated products Batch Culture: assume kd = 0 and qp = 0

6 Batch or Continuous Culture?

7 Batch or Continuous Culture?

8 Batch or Continuous Culture?

9 Batch or Continuous Culture? Most Bioprocesses are Based on Batch Culture In terms of number, mostly for secondary, high value products High Volume Bioprocesses are Based on Continuous Culture mostly for large volume, lower value, growth associated products such as ethanol production, waste treatment, single-cell protein production

10 The Ideal Chemostat An ideal chemostat is a perfectly mixed, continuousflow, stirred-tank reactor Most chemostats require some control elements (e.g. ph and DO controllers) Fresh sterile medium is fed to the completely mixed and aerated reactor, and cell suspension is removed at the same rate Liquid volume in the reactor is kept constant

11 Ideal Constant-Stirred Tank Reactor Chemostat

12 Mass Balance Statement for Cell Mass where: F = in and out volumetric flow rate (L / hr) X = bioreactor and outlet cell mass concentration (g /L) Xo = inlet cell mass concentration (g /L) µ = specific cell growth rate neglecting endogenous metabolism (hr-1) Kd = endogenous cell loss rate constant (hr-1)

13 Dilution rate Chemostats are normally operated at steady-state, dx/dt = 0. Assume a sterile feed (Xo = 0), and kd is so small that is neglected, kd = 0. The cell mass balance equations becomes,

14 Dilution rate So, by varying the medium supply, growth rate can be varied. This holds until D m Under these condition, the nutrient is no longer limiting Therefore, the expression ( -D) becomes -ve

15 Critical Dilution Rate The lowest dilution rate at which wash out occurs. D c is approximately equal to m. At dilution rates approaching D c, the chemostat becomes less stable since slight fluctuations in the flow rate. A major drawback of chemostat is that they work best at lower dilution rates where the changes in X and S are small.

16 Modified Bioreactors: Chemostat with Recycle To keep the cell concentration higher than the normal steady state level, cells in the effluent can be recycled back to the reactor Advantages of Cell Recycle Increase productivity for biomass production Increase stability by dampening perturbations of input stream properties

17 Chemostat with Recycle: Schematic Diagram

18 Chemostat with Recycle: Biomass Balance

19 Chemostat with Recycle: Biomass Balance

20 Chemostat with Recycle: Biomass Balance

21 Chemostat with Recycle: Comparison

22 Immobilized cell system Immobilized cell - Restriction of cell mobility within a confined space Potential Advantages: Provides high cell concentrations per unit of reactor volume. Eliminates the need for costly cell recovery and recycle. May allow very high volumetric productivities. May provide higher product yields, genetic stability, and shear damage protection. May provide favorable microenvironments such as cellcell contact, nutrient-product gradients, and ph gradients resulting in higher yields

23 Immobilized cell system Potential Disadvantages/Problems: If cells are growing (as opposed to being in stationary phase) and/or evolve gas (CO2), physical disruption of immobilization matrix could result. Products must be excreted from the cell to be recovered easily. Mass transfer limitations may occur as in immobilized enzyme systems.

24 Methods of Immobilization

25 Methods of Immobilization (cont d)

26 Methods of Immobilization (cont d)

27 Methods of Immobilization (cont d)

28 Methods of Immobilization (cont d) Binding Forces: Covalent Bonding: (review enzyme covalent bonding) Support materials: CMC-carbodiimide Support functional groups : -OH, -NH2, -COOH Binding to proteins on cell surface

29 Methods of Immobilization (cont d)

30 Methods of Immobilization (cont d)

Chapter 9: Operating Bioreactors

Chapter 9: Operating Bioreactors David Shonnard Department of Chemical Engineering 1 Presentation Outline: Choosing Cultivation Methods Modifying Batch and Continuous Reactors Immobilized Cell Systems