Bioreactor Analysis and OperationChapter 9&10 (textbook) • Overview of bioreactors • Modified batch and continuous reactors • Scale up/down • Immobilized cell systems • Operation consideration • Sterilization • Bioreactor Instrumentation and control
Bioreactor Analysis and Operation • Fermentation processes - solid state: water content: 40~ 80%, mostly mold fermentation on agriculture products and food: rice, wheat, barley, corn and soybean. e.g.rotary drum fermentator - submerged systems: water content > 95% e.g. bacteria, yeast.
Bioreactor Analysis and Operation • Overview of bioreactors for submerged system - Classification: operation modes: - batch: stirred tank - continuous: chemostat, fluidized-bed - modified types of the above modes: fed-batch, chemostat with recycle, multi-stage continuous reactors Oxygen supply: - aerobic: airlift - anaerobic • Form of biocatalyst: • free cell (enzyme) • immobilized cell (enzyme) • packed-bed, membrane reactor
Industrial Bioreactor Glacial Lakes Energy in Watertown, South Dakota 47+ million gallon per year ethanol production .
World's Largest Industrial Fermenter (Chem. Eng. News,10-Apr-78) The fermenter is 200' high and 25 ft diam.
Requirements for Cultivation Methods • Biomass concentration which must remain high • Sterile conditions being maintained • Effective agitation so that the distribution of substances in the reaction is uniform • Heat removal • Creation of the correct shear conditions - high may damage cells, low may lead to flocculation or growth on wall and stirrer
X1, S v Chemostat with Cell Recycle - To keep the cell concentration higher than the normal steady-state level in a chemostat. - To increase the cell and growth-associated product yield. - For low-product-value processes: e.g. waste treatment. fuel ethanol ,
Chemostat with Cell Recycle Cell mass balance (qp=0, kd ≈0, X0=0,Monod equation is applied): where µ=µnet=µg-kd A chemostat can be operated at dilution rates higher than the specific growth rate when cell recycle is used.
Chemostat with Cell Recycle When kd=0
Chemostat with Cell Recycle Mass balance on growth-limiting substrate (qp=0, kd ≈0, X0=0,Monod equation is applied):
Chemostat with Cell Recycle No recycle µm=1.00h-1, S0=2.0g/l, Ks=0.01 g/l, Yx/s=0.5 g/g, concentration factor C=2.0 and recycle ratio α=0.5
X1, S v Chemostat with Cell Recycle Cell mass balance around the cell separator.
Example-Chemostat with Cell Recycle Organisms are cultured in a chemostat with cell recycle. The system is operated under glucose limitation. Determine specific growth rate μnet, S in the reactor effluent, cell concentration in the recycle stream (CX1) and in the concentrator effluent (X2) If the concentrator has a volume of 300 mL, what is the residence time in it?
Fed-Batch Nutrients are continuously or semi-continuously fed, while effluent is removed discontinuously. - overcome substrate inhibition or catabolite repression by intermittent feeding of substrate by maintaining low substrate concentration. for production of secondary metabolites e.g. antibiotics, lactic acid, E. Coli making proteins from recombinant DNA technology.
Fed-Batch Analysis of fed-batch with substrate continuously fed and no output: t=0, V0=0, F is constant. Volume: At quasi steady state, S added=S consumed, X, S, P concentrations are constant. Cell mass balance: (Monod growth model applied)
Fed-Batch M where S≈0 assuming X≈Xm M where Xt=Xt0 at t=0
Fed-Batch (g) qp (i.e. g product/g cells-min) at Pt=Pt0, t=0
Example: Fed- Batch In a fed-batch culture operating with intermittent addition of glucose, the value of V is given at time t=2hr, when the system is at quasi-steady state. Determine V0. At t=2 hr, find S, X and Xt and P at quasi-steady state if qp=0.2 g product/g cells-h, P0=0.