Batch, fedbatch and continuous fermentation
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The document discusses different types of fermentation processes including batch, fed-batch, and continuous fermentation. It explains the key characteristics of each type such as whether the system is open or closed, and how substrates and cells are added or removed. The stages of microbial cell growth including lag phase, exponential phase, stationary phase, and death phase are also summarized for batch fermentation.
Batch, fedbatch and continuous fermentation
- 1. Batch, Fed-Batch and Continuous Fermentation Dr. Dhanya KC Assistant Professor, Department of Microbiology St. Mary’s College, Thrissur-680020, Kerala
- 2. Batch, Fed Batch and Continuous Fermentations Continuous - Open system Medium continuously fed Spent medium and cells removed continuously Volume remains constant Batch - Closed system Nutrients in a fixed volume Further additions - for pH control, aeration, etc. Fed-batch Medium or components fed continuously or intermittently Volume increases with time
- 3. Batch fermentation - Microbial cells - pass through a number of phases • Lag phase • Log or exponential phase • Stationary phase • Death or decline phase
- 4. Lag Phase Immediately after inoculation No apparent growth Time of adaptation Length - reduced – economical commercial Batch fermentation
- 5. Logarithmic or log or exponential phase Lag and log phase - trophophase Production of primary metabolites Amino acids, nucleotides, vitamins, citric acid, acetic acid, ethanol, etc. Growth rate of cells increases - Constant, Maximum rate dx/dt = µx x - Concentration of microbial biomass µ - Specific growth rate t - Time in hours Batch fermentation
- 6. Stationary Phase - Growth rate reduce Due to substrate limitation and toxin limitation Plot - biomass and initial substrate concentration Growth in different concentrations of substrates Initial increase in substrate - increase in biomass x = Y(S-SR) x - concentration of biomass Y - yield factor (g biomass / substrate) S - initial substrate concentration SR - residual substrate concentration Yield factor - efficiency of substrate conversion to biomass Batch fermentation
- 7. Death or decline phase - Cessation of growth - depletion of substrate Stationary and death phase – idiophase Secondary metabolites are formed Examples - antibiotics, pigments, toxins, etc Monod equation µ = µmax s/(Ks+ s) s -Residual substrate concentration Ks -substrate utilization constant substrate concentration when µ is half µmax A measure of the affinity for substrate µ - Specific growth rate µmax – Maximum Specific growth rate Batch fermentation
- 8. Death or decline phase - Cessation of growth - depletion of substrate Stationary and death phase – idiophase Secondary metabolites are formed Examples - antibiotics, pigments, toxins, etc Monod equation µ = µmax s/(Ks+ s) s -Residual substrate concentration Ks -substrate utilization constant substrate concentration when µ is half µmax A measure of the affinity for substrate µ - Specific growth rate µmax – Maximum Specific growth rate Batch fermentation
- 9. Application of batch fermentation Various growth conditions used for production of Biomass - fastest growth rate and maximum population 1o metabolite - extend exponential phase 2o metabolite - short exponential phase and extended production phase 1. Filling fermenter with medium 2. Sterilization of fermenter and medium 3. Inoculation 4. Production phase 5. Harvesting 6. Cleaning of vessel Disadvantages - High down time - non-productive period
- 10. Fed batch fermentation • Established initially in batch mode • Fed continuously or sequentially with medium • Without removal of culture fluid i) Same medium - increase in volume ii) Limiting substrate - same concentration - increase in volume iii) Limiting substrate - concentrated - increase in volume iv) Limiting substrate – very concentrated - no increase in volume i), ii) - variable volume fed batch system iv) - fixed volume fed batch system (iii) - intermediate between the variable and fixed volume systems
- 11. Continuous fermentation Fresh medium continuously added, Spent broth and cells are removed Exponential growth - prolonged Steady state achieved - new biomass balanced by loss of cells Dilution rate, D=F/V F is flow rate and V is the volume of vessel Change in cell mass over time, dx/dt = growth - output dx/dt = µx - Dx Under steady state concentrations, dx/dt will be zero, then µx = Dx µ = D
- 12. Continuous fermentation Under steady state conditions Specific growth rate is controlled by dilution rate Under steady state concentrations, dx/dt will be zero, then µx = Dx µ = D If dilution rate increase above µmax, complete washout of cells Dilution rate at which washout is just avoided is critical dilution rate (Dcrit)
- 13. Monod equation, µ = µmax s/(Ks+s) Chemostat - Substrate concentration is kept constant Turbidostat- Biomass concentration is kept constant At steady state, µ = D, so D = µmax ŝ/(Ks+ŝ) ŝ - steady state concentration of substrate ŝ = Ks D / (µmax - D) Substrate concentration is influenced by dilution rate Biomass depends upon substrate concentration and thereby on dilution rate Continuous fermentation
- 14. The concentration of cells in a chemostat at steady state ẍ = Y (SR- Sr) ẍ - steady-state cell concentration in chemostat SR - substrate concentration of inflowing medium Sr - steady-state residual substrate concentration Y - yield factor Biomass concentration under steady state conditions - controlled by Substrate feed concentration and Dilution rate Continuous fermentation
- 15. Advantages and disadvantages of continuous fermentation Down time - much less - more economic Easily automated - require less labour Chances of contamination and strain deterioration – more Control operations – complicated Problems in licensing of product - can’t trace product consignment to raw material batch
- 16. References 1. Industrial Microbiology: An Introduction, M J. Waites, N L. Morgan, J S. Rockey, G Higton 2. Principles of fermentation technology, PF Stanbury, A Whittakker, SJ Hall, 1995, Butterworth-Heinemann publications