Fermentation Technology
623311
Yalun Arifin
Chemical Engineering Dept.
University of Surabaya
1
Course content
I.
II.
III.
IV.
Introduction
General aspects of fermentation processes
Quantification of microbial rates
Stoichiometry of microbial growth and product
formation
V. Black box growth
VI. Growth and product formation
VII. Heat transfer in fermentation
VIII. Mass transfer in fermentation
IX. Unit operations in fermentation (introduction to
downstream processing)
X. Bioreactor
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Chapter I
Introduction
3
What is fermentation?
• Pasteur’s definition: “life without air”, anaerobe
red ox reactions in organisms
• New definition: a form of metabolism in which the
end products could be further oxidized
For example: a yeast cell obtains 2 molecules of ATP
per molecule of glucose when it ferments it to
ethanol
4
What is fermentation techniques (1)?
Techniques for large-scale production of microbial products.
It must both provide an optimum environment for the
microbial synthesis of the desired product and be
economically feasible on a large scale. They can be divided
into surface (emersion) and submersion techniques. The latter
may be run in batch, fed batch, continuous reactors
In the surface techniques, the microorganisms are cultivated
on the surface of a liquid or solid substrate. These techniques
are very complicated and rarely used in industry
5
What is fermentation techniques (2)?
In the submersion processes, the microorganisms grow in a
liquid medium. Except in traditional beer and wine
fermentation, the medium is held in fermenters and stirred to
obtain a homogeneous distribution of cells and medium. Most
processes are aerobic, and for these the medium must be
vigorously aerated. All important industrial processes
(production of biomass and protein, antibiotics, enzymes and
sewage treatment) are carried out by submersion processes.
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Some important fermentation products
Product
Ethanol
Glycerol
Lactic acid
Acetone and
butanol
-amylase
Organism
Saccharomyces
cerevisiae
Saccharomyces
cerevisiae
Lactobacillus
bulgaricus
Clostridium
acetobutylicum
Bacillus subtilis
Use
Industrial solvents,
beverages
Production of
explosives
Food and
pharmaceutical
Solvents
Starch hydrolysis
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Some important fermentation products
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Some important fermentation products
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Some important fermentation products
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Winemaking fermenter
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Chapter II
General Aspects of Fermentation
Processes
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Fermenter
The heart of the fermentation process is the fermenter.
In general:
• Stirred vessel, H/D  3
• Volume 1-1000 m3 (80 % filled)
• Biomass up to 100 kg dry weight/m3
• Product 10 mg/l –200 g/l
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Types of fermenter
•
•
•
•
•
•
Simple fermenters (batch and continuous)
Fed batch fermenter
Air-lift or bubble fermenter
Cyclone column fermenter
Tower fermenter
Other more advanced systems, etc
The size is few liters (laboratory use) - >500 m3
(industrial applications)
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Cross section of a fermenter for Penicillin production
( Copyright:
http://web.ukonline.co.uk/webwise/spinneret/microbes/penici.htm)
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Cross section of a fermenter for Penicillin production
( Copyright:
http://web.ukonline.co.uk/webwise/spinneret/microbes/penici.htm)
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Flow sheet of a multipurpose fermenter and its
auxiliary equipment
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Fermentation medium
• Define medium  nutritional, hormonal, and
substratum requirement of cells
• In most cases, the medium is independent of the
bioreactor design and process parameters
• The type: complex and synthetic medium (mineral
medium)
• Even small modifications in the medium could
change cell line stability, product quality, yield,
operational parameters, and downstream processing.
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Medium composition
Fermentation medium consists of:
• Macronutrients (C, H, N, S, P, Mg sources  water,
sugars, lipid, amino acids, salt minerals)
• Micronutrients (trace elements/ metals, vitamins)
• Additional factors: growth factors, attachment
proteins, transport proteins, etc)
For aerobic culture, oxygen is sparged
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Inoculums
Incoculum is the substance/ cell culture that is
introduced to the medium. The cell then grow in the
medium, conducting metabolisms.
Inoculum is prepared for the inoculation before the
fermentation starts.
It needs to be optimized for better performance:
• Adaptation in the medium
• Mutation (DNA recombinant, radiation, chemical
addition)
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Required value generation in fermenters as a
function of size and productivity
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Chapter III
Quantification of Microbial Rates
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Microbial rates of consumption or production
H2O
H+
C, N, P, S source
biomass
CO2
O2
product
heat
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What are the value of rates?
Rates of consumption or production are obtained from
mass balance over reactors
Mass balance over reactors
Transport + conversion = accumulation
(in – out) + (production – consumption) = accumulation
Batch: transport in = transport out = 0
Chemostat: accumulation = 0, steady state
Fed batch: transport out = 0
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How are rates defined?
Rate (ri) = amount i per hour / volume of reactor
kg.i / hour
m3  reactor
Biomass specific rate (qi)
qi = amount per hour / amount of organism in reactor
Thus:
kg.i / hour
kg. X
ri = qi CX
Substrate (-rS) = (-qS)CX
Biomass
rX = CX
Product
rP = qPCX
Oxygen (-rO2) = (-qO2)CX
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Yield = ratio of rates
Yij =
rj
q jC X
qj
rate. j



rate.i
ri
qiC X
qi
YSX = rate of biomass production / rate of substrate
consumption [g biomass/g substrate]
YOX = rate of biomass production / rate of oxygen
consumption [g biomass/g oxygen]
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Chapter IV
Stoichiometry of Microbial Growth and
Product Formation
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Introduction
Cell growth and product formation are complex processes
reflecting the overall kinetics and stoichiometry of the
thousands of intracellular reactions that can be observed within
a cell.
Thermodynamic limit is important for process optimization.
The complexity of the reactions can be represented by a simple
pseudochemical equation.
Several definitions have to be well understood before studying
this chapter, for example: YSXmax, YATP X, YOX, maintenance
coefficient based on substrate (ms).
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Composition of biomass
Molecules
• Protein 30-60 %
• Carbohydrate 5-30 %
• Lipid 5-10 %
• DNA 1 %
• RNA 5-15 %
• Ash (P, K+, Mg2+, etc)
•
•
•
•
•
•
•
Elements
C
40-50 %
H
7-10 %
O
20-30 %
N
5-10 %
P
1-3 %
Ash
3-10%
Typical composition biomass formula: C1H1.8O0.5N0.2
Suppose 1 kg dry biomass contains 5 % ash, what is the
amount of organic matter in C-mol biomass?
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Anabolism
Amino acids  protein
Sugars  carbohydrate
Fatty acids  lipids
Nucleotides  DNA, RNA
Sum of all reactions gives the anabolic reaction
energy
(…)C-source + (…)N-source + (…) P-source + O-source
C1H1.8O0.5N0.2 + (…)H2O + (…)CO2
Thermodynamically, energy is needed. Also for cells
maintenance
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Catabolism
Catabolism generates the energy needed for anabolism and
maintenance. It consist of electron donor couple and
electron donor acceptor couple
For example:
• Glucose + (…)O2  (…)HCO3- + H2O
donor couple: glucose/HCO3acceptor couple: O2/H2O
• Glucose  (…)HCO3- + (…)ethanol
donor couple: glucose/HCO3acceptor couple: CO2/ethanol
The catabolism produces Gibbs energy (Gcat.reaction)
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Coupled anabolism/catabolism
C-source (anabolism) and electron-donor (catabolism) are
often the same (e.g. organic substrate)
Only a fraction of the substrate ends in biomass as C-source,
while the rest is catabolized as electron-donor to provide
energy for anabolism and maintenance
YSX is the result of anabolic/catabolic coupling.
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Several examples stoichiometry of growth
Aerobic growth on oxalate
5.815 C2O42- + 0.2 NH4+ + 1.8575 O2 + 0.8 H+ + 5.415 H2O
 C1H1.8O0.5N0.2 + 10.63 HCO3What is C-source? N-source? Electron donor? Electron
acceptor?
YSX = 1 C-mol X / 5.815 mol oxalate = 1 C-mol X / 11.63 Cmol oxalate
Catabolic reaction for oxalate:
C2O42- + 0.5 O2 + H2O  2HCO3or H2C2O4 + 0.5 O2  H2O + 2CO2
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Aerobic growth on oxalate
Catabolism
3.715 C2O42- + 1.8575 O2 + 3.715 H2O  7.43 HCO3Anabolism (total-catabolism)
2.1 C2O42- + 0.2 NH4+ + 0.8 H+ + 1.700 H2O
 C1H1.8O0.5N0.2 + 3.2 HCO3Fraction of catabolism: 3.715/5.815 = 64 %
Fraction of anabolism: 2.1/5.815 = 36 %
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Microbial growth stoichiometry using
conservation principles
The general equation for growth stoichiometry
-1/YSX substrate + (…)N-source + (…)electron acceptor +
(…)H2O + (…)HCO3- + (…)H+ + C1H1.8O0.5N0.2 +
(…)oxidized substrate + (…)reduced acceptor
(…) > 0 for product, (…) < 0 for reactant
Note:
1. N-source, H2O, HCO3-, H+ and biomass are always present
2. Only substrate and electron acceptor are case specific
3. YSX is mostly available, all other coefficients follow the
element or charge conservation
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Aerobic growth of Pseudomonas oxalaticus
using NH4+ and oxalate (C2O42-)
Electron donor couple?
Electron acceptor couple?
C-source?
N-source?
YSX is 0.0506 gram biomass/ gram oxalate and biomass has 5
% ash. Biomass molecular weight = 24.6 g/C-mol X
YSX =
0.0506 * 88 * 0.95
 0.172 C-mol X/mol oxalate
24.6
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• Set up the general stoichiometric equation
f C2O42- + a NH4+ + b H+ + c O2 + d H2O  C1H1.8O0.5N0.2 +
e HCO3-
• Use YSX to calculate f
f= 
1
YSX

1
 5.815 mol oxalate/C-mol X
0.172
• There are 5 unknowns (a, b, c, d, e) and 5 conservation
balance (C, H, O, N, charge). For example:
C : 2f = 1 + e
H? O? N? charge?
• Solve for a, b, c, d, and e!
• What is the value of respiratory quotient (RQ)? Remember
RQ 
qCO2
qO2
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Microbial growth stoichiometry
Degree of reduction (i)
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What is degree of reduction (i)?
• It is about proton-electron balance in bioreactions
• Stoichiometric quantity of compound I
• Electron content of compound i relative to reference
atom
i
The references (i = 0):
C
+4
HCO3-/CO2
H
+1
+
H /OH
O
-2
NH4+/NH3
N
-3
SO42S
+6
Fe
+3
Fe3+
+ charge
-1
N-source for growth
- charge
+1
NH4+ as N-source
-3
N2 as N-source
0
NO3- as N-source
+5
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 for compounds
For example: glucose (C6H12O6)
 glucose = 6(4) + 12(1) + 6(-2) = 24 = 4/C-glucose
Biomass? O2? Fe2+? Citric acid? Ethanol? Lactic acid?
-balance
It is used to calculate stoichiometry
It follows from conservation relations (C, H, O, N, charge, etc)
by eliminating the unknown stoichiometric coefficient for
reference compounds
It relates biomass, substrate/donor, acceptor, product
(H2O, H+, HCO3-, N-source are always absent)
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Example
Catabolism of glucose to ethanol in anaerobic culture
-C6H12O6 + aC2H6O +bCO2 + cH2O +dH+

glucose = 24,  ethanol = 12,  balance = -24+12a = 0, a = 2
b, c, d follow from C,O, and charge conservation
Thus: -C6H12O6 + 2 C2H6O + 2 CO2
Try to solve:
a. Catabolism of ethanol to acetate (C2H3O2-) using O2/H2O
b. Catabolism of H2S to S- using NO3-/NO2c. Anabolic reaction, glucose as C-source and electron donor
d. Complete growth reaction, aerobic growth on oxalate
(C2O42-)
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Further reading
Stoichiometry calculations in undefined chemical systems for
fermentation with complex medium, biological waste
water treatment, and soluble and non-soluble compounds
Measurements of lumped quantities:
1. TOC, Carbon balance
2. Kj-N, Kjeldahl-nitrogen for all reduced nitrogen (organic
bound and NH4+), N-balance
3. ThOD, COD balance (similar to  balance)
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