During the years of my graduate studies in the USA at the University of Oklahoma and the University of Arkansas, the late Professor Mark Townsend gave me a lot of knowledge and assisted me in my academic achievements. Jahanshahi, from the University of Mazandaran, Iran, and Dr Nidal Hilal from the University of Nottingham, UK.
Industrial Microbiology
- INTRODUCTION
- PROCESS FERMENTATION
- APPLICATION OF FERMENTATION PROCESSES
- BIOPROCESS PRODUCTS
- Biomass
- Cell Products
- Modified Compounds (Biotransformation)
- PRODUCTION OF LACTIC ACID
- PRODUCTION OF VINEGAR
- PRODUCTION OF AMINO ACIDS (LYSINE AND GLUTAMIC ACID) AND INSULINGLUTAMIC ACID) AND INSULIN
- Stepwise Amino Acid Production
- Insulin
- ANTIBIOTICS, PRODUCTION OF PENICILLIN
- PRODUCTION OF ENZYMES
- PRODUCTION OF BAKER’S YEAST
Commercial production of biomass is seen in the production of baker's yeast used in the baking industry. Large amounts of whey are a waste product in the production of dairy products such as cheese.
Dissolved Oxygen Measurement and Mixing
- INTRODUCTION
- MEASUREMENT OF DISSOLVED OXYGEN CONCENTRATIONS The concentration of dissolved oxygen in a fermenter is normally measured with a dissolvedThe concentration of dissolved oxygen in a fermenter is normally measured with a dissolved
- BATCH AND CONTINUOUS FERMENTATION FOR PRODUCTION OF SCPPRODUCTION OF SCP
- Analytical Methods for Measuring Protein Content of Baker’s Yeast (SCP)Baker’s Yeast (SCP)
- Seed Culture
- BATCH EXPERIMENT FOR PRODUCTION OF BAKER’S YEASTBAKER’S YEAST
- OXYGEN TRANSFER RATE (OTR)
- RESPIRATION QUOTIENT (RQ)
- AGITATION RATE STUDIES
- NOMENCLATURE
In the following experiment we will assume that the optimum air flow rate of 0.5 vvm is desired. The solubility of oxygen in the fermentation broth is approximately 8⫻10⫺3kg m⫺3.9 The specific oxygen uptake rate is 12.5 mmol g⫺1h⫺1.
Gas and Liquid System (Aeration and Agitation)
INTRODUCTION
AERATION AND AGITATION
The growth of aerobic bacteria in the fermenter is controlled by the availability of substrate, energy and enzymes. Aerobic activity depends on the local total oxygen concentration, the oxygen diffusion coefficient and the rate of microbial respiration in the aerobic zone.
EFFECT OF AGITATION ON DISSOLVED OXYGEN
Microbial cultures are always known as heterogeneous systems, since the cells are solid and the nutrients are in the liquid phase. If the process is aerobic, air must be supplied to increase cell growth, otherwise limited dissolved oxygen is used up and then oxygen limitation may cause a decrease in growth rate.
AIR SPARGER
Several sets of rotors are used to ensure even gas distribution in the fermentation slurry. A wide selection of impellers is available; other forms of impellers associated with mixing and stirring bioreactors are discussed in the literature.2 In this book the term "bioreactor".
OXYGEN TRANSFER RATE IN A FERMENTER
- Mass Transfer in a Gas–Liquid System
3.5.1.1) where NA is the oxygen flow in kmol m⫺2s⫺1, kLi is the mass transfer coefficient on the liquid side in m/s, Ci is the oxygen concentration at the boundary in kmol m⫺3 and CL is the oxygen concentration in the liquid mass. The molar flow of oxygen from the gas phase to the liquid phase is also given as:.
MASS TRANSFER COEFFICIENTS FOR STIRRED TANKS
Thus, more input power is required to achieve the same value of mass transfer coefficient than in a Newtonian fluid. The addition of antifoam has a significant effect on the value of the mass transfer coefficient.
GAS HOLD-UP
AGITATED SYSTEM AND MIXING PHENOMENA
CHARACTERISATION OF AGITATION
The third group, which is related to the energy required by the mixer, is the power number. Energy consumption is related to the properties of the liquid, the density and viscosity of the liquid, the speed of rotation of the mixer and the diameter of the rotor.
TYPES OF AGITATOR There are four types of agitator commonly used in the bioreactors:There are four types of agitator commonly used in the bioreactors
These runners are classified as remote types, having a diameter in the range of 25-67% of the tank diameter. If we compare the disc turbine mixer with the intermig mixer, this type has a more even transfer of energy to the liquid in the container.
GAS–LIQUID PHASE MASS TRANSFER
- Oxygen Transport
- Diameter of Gas Bubble Formed D 0
Using the ideal gas law (PV⫽nRT), we then solve for moles of oxygen used in the bioreactor. The molar transformation of oxygen in the gas phase is proportional to the pressure gradient:.
CASE STUDY: OXYGEN TRANSFER RATE MODEL IN AN AERATED TANK FOR PHARMACEUTICAL WASTEWATERAN AERATED TANK FOR PHARMACEUTICAL WASTEWATER
- Introduction
- Material and Method
- Results and Discussion
Reduction of chemical equivalent of carbohydrate for the small aeration tank with airflow rates of 1.3 liters/min was shown in the previous chapter, Figure 2.1. The experimental data presented in Figure 3.6 show good agreement for an airflow rate of 10 litres/min.
CASE STUDY: FUEL AND CHEMICAL PRODUCTION FROM THE WATER GAS SHIFT REACTION BY FERMENTATION PROCESSESTHE WATER GAS SHIFT REACTION BY FERMENTATION PROCESSES
- Introduction
- Kinetics of Growth in a Batch Bioreactor
- Effect of Substrate Concentration on Microbial Growth
- Mass Transfer Phenomena
- Kinetic of Water Gas Shift Reaction
- Growth Kinetics of CO Substrate on Clostridium ljungdahlii
- Acknowledgements
Thus, the rate of mass transfer can be proportional to the partial pressure of CO in the gas phase, as expected by . Also, a decrease in the partial pressure of carbon monoxide was influenced by the acetate concentration in the culture media. PCO,gas Partial pressure of CO in the gas phase, atm PCO,liquid Partial pressure of CO in the liquid phase, atm.
Fermentation Process Control
- INTRODUCTION
- BIOREACTOR CONTROLLING PROBES
- CHARACTERISTICS OF BIOREACTOR SENSORS
- TEMPERATURE MEASUREMENT AND CONTROL
- DO MEASUREMENT AND CONTROL
- pH/REDOX MEASUREMENT AND CONTROL
- DETECTION AND PREVENTION OF THE FOAM
- BIOSENSORS
The electrical signal produced by the probe is directly proportional to the concentration of dissolved oxygen in the liquid. Due to the evaporation of the liquid medium, there may be problems with dirt on the electrode due to soup. A foam detector based on the resistive method works on the conductivity of the probe.
Growth Kinetics
INTRODUCTION
CELL GROWTH IN BATCH CULTURE
GROWTH PHASES
At this stage, a death phase develops while the cell density drops drastically if the toxic secondary metabolites are present. The death phase shows an exponential decrease in the number of living cells in the media as nutrients are depleted.
KINETICS OF BATCH CULTURE
There is no removal of cells from the batch vessel and the rate of cell reproduction is proportional to the specific growth rate, m(h⫺1), using the differential growth equation the cell concentration versus time is:.
GROWTH KINETICS FOR CONTINUOUS CULTURE
Cell concentration is controlled by the supplied nutrients and the flow rate of fresh media. Substrate concentration and residence time in the fermenter can determine cell density. The use of substrate and the kinetic expressions for all fermenters are quite similar.
MATERIAL BALANCE FOR CSTR
- Rate of Product Formation Similarly, the rate of product formation is defined as:Similarly, the rate of product formation is defined as
- Continuous Culture
- Disadvantages of Batch Culture
- Advantages of Continuous Culture
- Biomass Balances (Cells) in a Bioreactor The material balance for cells in a continuous culture chemostat is defined as:The material balance for cells in a continuous culture chemostat is defined as
- Material Balance in Terms of Substrate in a Chemostat The substrate balance is given based on following equation:The substrate balance is given based on following equation
- Modified Chemostat
- Fed Batch Culture
For a special case, the specific growth rate for product formation is simplified and reduced to:. At steady state, the biomass concentration remains constant, i.e. dX/dt⫽0, and (5.6.1.3) concludes to m⫽D; therefore, the specific growth rate is equal to the dilution rate. Material balance in a chemostat with recycle,rcell:. c⫽the factor by which the exhaust stream is concentrated before return d. Chemostat with a cell recycling stream.
ENZYME REACTION KINETICS
- Mechanisms of Single Enzyme with Dual Substrates The kinetics of double substrates with defined dissociation constants are given as:The kinetics of double substrates with defined dissociation constants are given as
- Reaction Mechanism with Competitive Inhibition
- Non-competitive Inhibition Rate Model
We know the total enzyme concentration as the sum of the conjugated enzymes with substrates and the free enzymes. It is also assumed that EIS does not react further and is unable to deliver any product P. The availability equation for non-competitive inhibition, umax, is affected:. 5.7.4.6) The competitive and non-competitive inhibitors are easily distinguished in a Lineweaver–. The competitive inhibitor intercepts on 1/yaxis, while the non-competitive inhibitor intercepts on 1/Saxis.
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CASE STUDY: ENZYME KINETIC MODELS FOR RESOLUTION OF RACEMIC IBUPROFEN ESTERS IN A MEMBRANE REACTORRACEMIC IBUPROFEN ESTERS IN A MEMBRANE REACTOR
- Introduction
- Enzyme Kinetics
- Enzyme Kinetics for Rapid Equilibrium System (quasi-equilibrium)(quasi-equilibrium)
- Derivation of Enzymatic Rate Equation from Rapid Equilibrium AssumptionRapid Equilibrium Assumption
- Verification of Kinetic Mechanism
In this case study, the kinetic behavior of the immobilized system was analyzed taking into account the following parameters:. a) the rate equations for native enzymes and immobilized enzymes are not necessarily the same due to microenvironment and shear stress effects; A known concentration of 2-ethoxyethanol was added to the organic phase before the start of the product inhibition reaction. In the absence of inhibition, enzyme kinetics are reduced to the simplest Michaelis-Menten model, as shown in Figure 5.21.
Bioreactor Design
INTRODUCTION
BACKGROUND TO BIOREACTORS
TYPE OF BIOREACTOR
- Airlift Bioreactors
- Airlift Pressure Cycle Bioreactors
- Loop Bioreactor
Mechanical stirrers are installed at the top or bottom of the tank for adequate mixing. In the usual form, air is introduced into the bottom of a central draft tube through a diffuser ring, which reduces the apparent density of the liquid in the tube relative to the annular space of the bioreactor. The degassed liquid then flows down into the annular space outside the draft to the bottom of the bioreactor.
STIRRED TANK BIOREACTORS
In a large container, the height of liquid can be as high as 60 m, the pressure at the bottom of the container will increase the oxygen solubility, and the value of KLa will increase. Sprayers must always be located near the bottom of the vessel with a distance Di/2 below the agitator, where Diis is the diameter of the impellers. The simplest devices have rakes mounted on the stirring shaft located on the surface of the liquid.
BUBBLE COLUMN FERMENTER
The nutrient solution in the foam flows back into the bioreactor and the air released from the foam leaves the vessel. There must be a minimum number of openings in the bioreactor so that sterility can be maintained. One of the most difficult areas to seal effectively is where the rudder shaft enters the vessel; a double mechanical seal must be fitted here.
AIRLIFT BIOREACTORS
Although an agitator is not required, greater air circulation is necessary and the air must be at a higher pressure, especially on a large scale. Separation of gas from liquid is not very efficient when foam is present. However, air must enter mainly from the bottom to circulate the liquid through the reactor.
HEAT TRANSFER
The overall heat transfer coefficient depends on the stirring speed in the vessel, the throughput of the liquid and gas in an airlift bioreactor, and the circulation rate of the cooling water in the jacket. The expected value of the total heat transfer coefficient including all resistances for an anti-fouling system should be between 500 and 1500 W⭈m⫺2⭈K⫺1. Therefore, the heat transfer area can be maximized by having both cooling water in the baffles and in the jacket of the bioreactor.
DESIGN EQUATIONS FOR CSTR FERMENTER
- Monod Model for a Chemostat
The cell mass concentration is defined by the dilution rate approaching zero; the cell density is the product of yield and initial substrate concentration:. As the dilution rate increases, the concentration level of the final substrate will increase linearly with D, and Dapproaches mmax. Near the washout, the reactor is very sensitive to variations in the dilution rate D. A small change in D produces a relatively large shift in X and S. The cell production rate per volume unit of the reactor is DX.
TEMPERATURE EFFECT ON RATE CONSTANT
Rearranging gives a second-order equation with respect to D:. reaction rate constant can follow Arrhenius law. 6.9.1) Integration can lead to a relation for rate constant with temperature dependence in the form of Arrhenius' law:.
SCALE-UP OF STIRRED-TANK BIOREACTOR
This is usually not a practical situation, and generally the Reynolds number always increases in the process of scaling up. Power number versus Reynolds number for various propellers (flat blade, turbine, bladed disk, and marine propeller). Using the graph of Pg/Pversus Na (Figure 6.7), the ratio of carbonated power to non-carbonated power is determined.
Downstream Processing
- INTRODUCTION
- DOWNSTREAM PROCESSING
- FILTRATION
- Theory of Filtration
- CENTRIFUGATION
- Theory of Centrifugation
- SEDIMENTATION
- FLOTATION
- EMERGING TECHNOLOGY FOR CELL RECOVERY
- CELL DISRUPTION
- SOLVENT EXTRACTION
- Product Recovery by Liquid–Liquid Extraction
Filter aid can be added to the fermentation broth to increase the porosity of the cake during molding. In (7.4.1.1), centrifugal force is applied to obtain the terminal velocity in the centrifuge, where u is the particle velocity in the centrifuge relative to the angular velocity of the bowl in rad/s, and r is the radius of the bowl or centrifuge drum . Amyl acetate or butyl acetate is used as an organic solvent to remove most of the product from the fermentation broth.
