Ghasem D. Najafpour. Biochemical Engineering and Biotechnology
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From the graph, the overall heat transfer coefficient for jacketed vessel
7
is
U ⬇100 Btuh
1
ft
2
F
1
(E.6.3)
(E.6.4)
(E.6.5)
The power for the fermentation vessel was projected by the following general equation
(E.6.6)
From Kern
7
page 718, with the given Re, read hD/k 2000
Assuming the thickness of jacket 1 in
Dirt factor,
R
d
0.005
11 1
300
0 005 1
UU
R
De
d
2
20 Btu/hr ft F .
U
hh
hh
c
io
io
2
0 Btu/hr ft F
550 600
1150
30
h
cold water
2
550 Btu/hr ft F⬇
h
2000 0 356
3075
60
.
.
0 Btu/hr ft F
2
D
D
i
t
1
3
Re
ND
ft
r
m
i
75
2
2
3
62 4 30 000 0
242
43 10
(.)(, )(. )
.
.
Power(hp)
129 10
4 1 1 2 72 2 86 0 3 0 6 0 14 0 86
.
.. . . . . .
DL N wH mr
h
h
D
D
N
N
1
2
1
2
12
1
2
Ê
Ë
Á
ˆ
¯
˜
Ê
Ë
Á
ˆ
¯
˜
/
Nu
hD
k
Re Pr
t
036
23 13
.
//
Re
ND
r
m
i
2
324 BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY
Ch013.qxd 11/21/2006 9:51 AM Page 324
The inlet and outlet temperature of the jacketed bioreactor is shown in Figure E.6.1. The log
mean temperature is:
Heat transfer based resistance theory for composite wall. The heat transfer overall coeffi-
cient is calculated.
(E.6.7)
Heat transfer area,
(E.6.8)
Q (24.45)(120)(1.8)(11.27) 350,000 Btuh
1
(E.6.9)
Mass flow rate of cooling water 35000 lb
m
h
1
13.6 AEROBIC WASTEWATER TREATMENT
The well-known aerobic downflow process is a trickled bed filter. Attached growth is used
in the biological treatment of wastewater. Air passes through the bed while the liquid is
forced to down by gravity. Figure 13.2 shows the liquid gas system for the mass transfer
QAUT
D
ln
AD DH [( ) ( )] [( . ) ( . )] .
22
4 225 4 3225 2425//ft
L
2
11 1
Uh
x
kh
io
T
ln
()()
ln
.
32 15 32 25
17
7
11 27
Ê
Ë
Á
ˆ
¯
˜
C
BIOPROCESS SCALE-UP 325
T=32°C
t
C, out
= 25°C
t
C, in
=15°C
FIG. E.6.2. Temperature pattern in a jacketed bioreactor for log mean temperature.
Ch013.qxd 11/21/2006 9:51 AM Page 325
process in a biological filter. The system is known as attached growth. Modes of bioreac-
tor operation are:
• Batch
• Fed batch
• Continuous
(13.6.1)
For batch operation
(13.6.2)
(13.6.3)
(13.6.4)
V constant
(13.6.5)
(13.6.6)
(13.6.7)
where, S
0
and S
f
are initial and final substrate concentration in moll
1
.
t
KS
S
SS
batch
Mf
o
f0
nn
max max
ln ( )+
1
dd
M
t
KS
vS
S
t
S
S
0
0
ÚÚ
Ê
Ë
Á
ˆ
¯
˜
max
d
d
M
S
t
S
KS
n
max
r
C
t
A
A
d
d
rr
V
SV
t
S
KS
SA
M
d
d
1( )
max
n
mm
io
0
d
d
ioPS
m
t
mmrr
326 BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY
Down
flow
Air
Air
Air
Influent
FIG. 13.2. Liquid gas mass transfer process in biological filter, attached growth system.
Ch013.qxd 11/21/2006 9:51 AM Page 326
13.6.1 Substrate Balance in a Continuous System
(13.6.1.1)
(13.6.1.2)
At steady-state condition
(13.6.1.3)
(13.6.1.4)
(13.6.1.5)
when
(13.6.1.6)
(13.6.1.7)
(13.6.1.8)
Example 1
For production of an enzyme used for synthesis of a sun protection lotion, the required
kinetic data and constants are:
n
max
2.3 mmolm
3
s
1
d
d
tank
o
E
RT
t
E
RT
kke
2
r
cell i
YSS
xs
()
m D
DS S
P
Y
P
Y
qP
Y
i
xs
xs
p
ps
()
m
m
cell
cell
cell
for SCP
for ethanol
mP
P
Y
sx
cell
cell
m
d
d
S
t
0
Glucose
ATP P ADP 7.8 kcal
i
æÆæææææææ GP6
d
d
i
cell
Yield of cell
cell
cell
Nut
S
t
F
V
SS
P
Y
mP
qP
Y
xs
p
ps
()
m
rrient maintenance
BIOPROCESS SCALE-UP 327
Ch013.qxd 11/21/2006 9:51 AM Page 327
K
m
8.9 mmoll
1
S
o
12 mmoll
1
Find the reaction time for 95% conversion of raw materials.
t
batch
? for x
A
0.95
Solution
13.6.2 Material Balance in Fed Batch
In fact, fed batch is a batch system operating without any outlet stream. The differences in
substrate in and out are equal to the rate of product generation.
(13.6.2.1)
The retention time:
(13.6.2.2)
(13.6.2.3)
(13.6.2.4)
d
d
cell
stead
y
state
io
sterile system
gr
r
rr m
t
F
V
0
Ê
Ë
Á
Á
ˆ
¯
˜
˜
oowth
death
cell
ar
Ê
Ë
Á
Á
ˆ
¯
˜
˜
DS S
S
KS
m
()
max
i
y
t
1
D
V
F
F
V
SS
S
KS
V
V
()
max
i
m
y
Ê
Ë
Á
ˆ
¯
˜
t
K
S
S
SS
batch
m
o
f
of
yy
max max
ln
.
ln
(.)()
.89
9
12
1 0 95 12
095 12
99
4 .2 hours
y
max
2.5 mmol
ms
3600 s
h
1 m
1000 L
9 mmo
3
3
Ê
Ë
Á
ˆ
¯
˜
Ê
Ë
Á
ˆ
¯
˜
Ê
Ë
Á
ˆ
¯
˜
ll
Lh
328 BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY
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The simplified material balance would lead to growth rate
(13.6.2.5)
Example 1
A 10 m
3
bioreactor with H/d 2.5D, 75% working volume, with two sets of standard flat-
blade impellers was used for a baker’s yeast production unit. The operating dilution rate
was set at 0.5h
1
. The rate equation satisfying the reactor design was a Monod model with
m
max
0.65 h
1
and k
S
3kgm
3
. The initial substrate concentration was 65 gl
1
with 1vvm
aeration, broth density 1200 kgm
3
and viscosity m 0.02 Nsm
2
. The yield of biomass on
glucose was 0.5g cellg
1
glucose. Calculate power consumption for a 90 rpm agitation rate
and OTR of 0.05 gl
1
. State the controlling resistance in the mass transfer process.
Solution
The flow regime is turbulent flow. Read the value for the power number using Figure 6.6,
Chapter 6.
where N
a
is known as the aeration number, then use Figure 6.7 in Chapter 6 to find the ratio
of gassed power to ungassed power.
P
g
r
095.
N
F
D
a
g
i
3
3
7.5m min
90 rpm 0.57
m
3
045
()()
.
N
p
6
Re
(. )(. )( )
.
.
1 0 57 1200
002
29 10
2
4
5 rps
Ns
m
2
10
4
25
1
05
2
.
.
.
DD
D
D
(
)
t
i
7 m
7 m
m
F
V
BIOPROCESS SCALE-UP 329
Ch013.qxd 11/21/2006 9:51 AM Page 329
Conversion factor:
1hp 745.7 kgms
1
Oxygen transfer rate
Liquid film was the controlling resistance.
13.7 NOMENCLATURE
N Impeller speed, rpm
D
i
Impeller diameter, m
Q
O
2
Oxygen transfer rate, mmolmin
1
X Biomass concentration, gl
1
P
g
/V Power per unit volume, hpm
3
V
K
s
L
7.5m /min
/4 1.72
3.23m/min 194m h
210 cm
3
2
1
3
()( )
(323 //min 0.051 7.9 10 S
0.7 0.2 4 1
)( )
OTR K a C C
KV
LL
Ls
(). (.)
.
79 10 003
410
210
4
5
3
0
kg.m s
31
77
02
P
V
L
g
Ê
Ë
Á
ˆ
¯
˜
.
P
V
L
g
1
w.l
0 051.
P
g
8 hp09504 03.(.) .
P 202 0. .4 hp
N
Pg
nD
P
c
p
i
3
kg m
s
r
3
35
6 1200 1 5 0 57
981
149
149
745 7
0
(.)(. )
.
.
.22 hp
330 BIOCHEMICAL ENGINEERING AND BIOTECHNOLOGY
Ch013.qxd 11/21/2006 9:51 AM Page 330
ND
i
Impeller tip velocity, ms
1
t
m
Mixing time, min
K
L
a Mass transfer coefficient, h
1
t Shear stress, Pa
Shear rate, s
1
m Fluid viscosity, cp
Froude Number, dimensionless
H
i
Impeller interspacing, cm
U
g
Upward gas bubble velocity,ms
1
g Gravity, ms
2
OTR Oxygen transfer rate, kmol.m
3
h
1
V
S
, U
S
Gas superficial velocity, ms
1
K
m
Monod rate constant, gl
1
n
max
Maximum specific growth rate, mmolm
3
s
1
kx Maximum specific growth rate., gl
1
h
1
D Fresh media dilution rate, h
1
F Flow rate, mlmin
1
V Volume, m
3
Y
X/S
Yield of biomass on substrate
S
f
Inlet to outlet substrate ratio
R Recycle ratio
f Ratio inlet to outlet substrate concentration
REFERENCES
1. Scragg, A.H., “Bioreactors in Biotechnology, A Practical Approach”. Ellis Horwood Series in Biochemistry
and Biotechnology, New York, 1991.
2. Wang, D.I.C., Cooney, C.L., Deman, A.L., Dunnill, P., Humphrey, A.E. and Lilly, M.D., “Fermentation and
Enzyme Technology”. John Wiley & Sons, New York, 1979.
3. Baily, J.E. and Ollis, D.F., “Biochemical Engineering Fundamentals”, 2nd edn. McGraw-Hill, New York, 1986.
4. Doran, P.M., “Bioprocess Engineering Principles”. Academic Press, New York, 1995.
5. Michel, B.J. and Miller, S.A., AIChE J. 8, 262 (1962).
6. Stanbury, P.F. and Whitaker, A., “Principles of Fermentation Technology”. Pergamon Press, Oxford, 1984.
7. Kern, D., “Process Heat Transfer”. McGraw Hill, New York, 1950, p. 717.
ND
g
2
i
d
d
u
x
BIOPROCESS SCALE-UP 331
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CHAPTER 14
Single-Cell Protein
14.1 INTRODUCTION
The term single-cell protein (SCP) is used to describe protein derived from cells of micro-
organisms such as yeast, fungi, algae and bacteria which are grown on various carbon
sources for synthesis. The dried cells of microorganisms or the whole organism is harvested
and consumed. This is a protein source for human food supplements and animal feeds. SCP
production may have potential for feeding the ever-increasing world population. Massive
quantities of SCP can be produced in a single day. As a source of protein it is very promis-
ing, with potential to satisfy the world shortage of food while population increases.
There are several carbon sources that are used as energy sources for microorganisms
for growing and producing CSP. In some cases, raw material requires pretreatment or
hydrolysis before use. Waste sources of carbon are customary and cheap to use. SCP tech-
nology is a suitable process for converting waste materials to useful biomass containing
protein. The broth is concentrated protein which is then dried with limited moisture; it is
stored for use as food or feed for humans and animals. Waste recycling has been advanced
as a method for preventing environmental decay and increasing food supplies. It may be
possible to convert waste streams into valuable products by separation and recovery or by
biological conversion.
1–4
Many products are produced biologically from food process
waste. The potential benefits of successful recycling of agricultural wastes are enormous.
It may be the only method for large-scale protein production that does not require a con-
comitant increase in energy consumption. In addition, it may be the most effective method
for producing animal and human food from lignocellulose materials that are otherwise of
little nutritive value and are therefore used for fuel production. One advantage of the bio-
logical process is the flexibility of the microorganisms to adapt to different feedstocks.
Therefore, when combined with the treatment of process waste streams, the biological con-
version of these wastes to products can be both environmentally and economically
favourable.
In the production of antibiotics, sufficient growth of fungi in submerged cultures has cre-
ated potential sources of biomass as SCP and as flavour additives to replace mushrooms:
the biomass contains 50–65% protein.
1,5
Production of mushroom from lignocellulosic
waste seems to be a suitable and economical process since the raw material is inexpensive
and available in most countries.
332
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SINGLE-CELL PROTEIN 333
This chapter discusses the present status of microbial SCP production from agricultural
wastes and describes some of the technical and economical problems related to the pro-
duction processes that must be overcome for large-scale application to be possible.
14.2 SEPARATION OF MICROBIAL BIOMASS
Bacteria, yeast and algae are produced in massive quantities of protein sources as food for
animals and humans.
1
SCP is considered a major source of feed for animals. The produc-
tion of valuable biological products from industrial and agricultural wastes is considered
through the bioconversion of solid wastes to added-value fermented product, which is eas-
ily marketable as animal feedstock. The waste streams that otherwise would cause pollu-
tion and threaten the environment can be considered raw material for CSP production using
suitable strains of microorganisms.
14.3 BACKGROUND
It is evident that the conversion of photosynthetically produced organic compounds into
human and animal food is the limiting process in human food production. The worldwide
annual production of organic material by photosynthesis has been estimated to be between
25 and 50 tons.
5,6
Any practical method capable of converting a small fraction of this yield
into human food should find wide application and go a long way to reducing chronic food
shortages.
The growth of microorganisms, more rapid than that of the higher plants, makes them very
attractive as high-protein crops; whereas only one or two grain crops can be grown per year,
a crop of yeasts or moulds may be harvested weekly, and bacteria may be harvested daily. The
use of microorganisms as a source of protein for human and animal food is not a new devel-
opment. Traditional foods and feeds such as cheese, sauerkraut, miso and silage have a high
content of microorganisms to which their nutritional properties are due in part. The high-
quality proteins synthesised during the growth of these microorganisms compare favourably
with those derived from the better grains.
1,3
There are many convincing reports on the avail-
ability of essential amino acids and the protein quality of SCP. Although there are few data
on animal feeding trials using SCP produced from lignocellulose wastes, there is a large and
growing body of information about SCP from petroleum and methanol. This information
should be applicable to SCP from agricultural wastes with proper allowance for the undesir-
able contaminants in the sources. In petroleum, there has been concern about accumulation
of carcinogenic hydrocarbons. In agricultural wastes, there is concern about accumulation of
pesticides and herbicides. The guidelines for testing SCP as a major supplement in animal
diets and should be consulted for further details on feeding trials. Many more feeding trials
will be needed before SCP from lignocellulose wastes is accepted for routine feeding.
The main carbon source for production of SCP is petroleum. It has been practised
in many companies around the world. Other potential substrates for SCP include bagasse,
citrus wastes, sulphite waste liquor from pulp and paper, molasses, animal manure, whey,
starch, sewage and agricultural wastes.
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