Bioreactor System ERT 314 Sidang 1 2010/2011
Chapter 2:Types of Bioreactors Week 2
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
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fresh nutrient medium is continually supplied to a well-mixed culture, and products and cells are simultaneously withdrawn Growth and product formation can be maintained for prolonged periods of time At steady state, cell, product, and substrate concentrations remain constant
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
Batch or Continuous Culture?
Batch or Continuous Culture?
Batch or Continuous Culture?
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
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
Ideal Constant-Stirred Tank Reactor Chemostat
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)
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,
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
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.
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
Chemostat with Recycle: Schematic Diagram
Chemostat with Recycle: Biomass Balance
Chemostat with Recycle: Biomass Balance
Chemostat with Recycle: Biomass Balance
Chemostat with Recycle: Comparison
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
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.
Methods of Immobilization
Methods of Immobilization (cont d)
Methods of Immobilization (cont d)
Methods of Immobilization (cont d)
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
Methods of Immobilization (cont d)
Methods of Immobilization (cont d)