bubble coalescence can be neglected. It was assumed that below this gas velocity
the difference between k L a values in distilled water, in cultivation media in the
presence and absence of AFA, is caused by only k L and that this difference in k L
holds true for higher gas velocities as well. Above this critical superficial gas
velocity the volumetric mass transfer coefficient due to the specific interfacial
area is enhanced, but the bubble coalescence is also increased, which reduces
the specific interfacial area. In order to compare the specific interfacial area of
the investigated systems in the presence and absence of AFAs, the coalescence
index m corr was defined, which was corrected by the difference in k L values in
water, nutrient medium and cultivation medium [39].
(k L a) corr
m corr = 04
(3)
(k L a) ref
where (k L a) ref is the volumetric mass transfer coefficient in the reference
system.
(k L a) corr = k L a – D(k L a)
( 3 a )
and k L a is the volumetric mass transfer coefficient in the cultivation medium:
[Dk L a = k L a – (k L a) ref ] at w SG = 2 cm s –1
(3b)
A nutrient salt solution with an antifoam agent had the lowest k L a value, and
therefore it was chosen as the reference system.
In Table 1, m corr values for various biological systems and nutrient salt
solutions with an antifoam agent [Desmophen 3600, Bayer AG, a poly(propylene
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
201
Table 1. Values of m corr for biological systems and nutrient salt solution in a bubble column at
w SG = 4 cm s –1 . The reference is the nutrient salt solution with Desmophen which has the
lowest k L a value [40]
Biological system
Substrate (Antifoam)
m corr
Chaetomium cellulolyticum glucose (no antifoam)
2.56
C. cellulolyticum
glucose (small amount of Desmophen) 1.21
Escherichia coli
casein
(small amount of Desmophen) 1.40
peptone
Saccharomyces cerevisiae
glucose (small amount of Desmophen) 1.22
Hansenula polymorpha
glucose (small amount of Desmophen) 2.29
H. polymorpha
glucose (small amount of Desmophen) (with substrate
limitation 2.17)
H. polymorpha
ethanol (small amount of silicon oil)
1.52 (with oxygen
transfer limitation)
H. polymorpha
ethanol (small amount of Desmophen) 1.52 (with substrate
limitation)
Nutrient salt solution
(no antifoam)
2.29
the difference between k L a values in distilled water, in cultivation media in the
presence and absence of AFA, is caused by only k L and that this difference in k L
holds true for higher gas velocities as well. Above this critical superficial gas
velocity the volumetric mass transfer coefficient due to the specific interfacial
area is enhanced, but the bubble coalescence is also increased, which reduces
the specific interfacial area. In order to compare the specific interfacial area of
the investigated systems in the presence and absence of AFAs, the coalescence
index m corr was defined, which was corrected by the difference in k L values in
water, nutrient medium and cultivation medium [39].
(k L a) corr
m corr = 04
(3)
(k L a) ref
where (k L a) ref is the volumetric mass transfer coefficient in the reference
system.
(k L a) corr = k L a – D(k L a)
( 3 a )
and k L a is the volumetric mass transfer coefficient in the cultivation medium:
[Dk L a = k L a – (k L a) ref ] at w SG = 2 cm s –1
(3b)
A nutrient salt solution with an antifoam agent had the lowest k L a value, and
therefore it was chosen as the reference system.
In Table 1, m corr values for various biological systems and nutrient salt
solutions with an antifoam agent [Desmophen 3600, Bayer AG, a poly(propylene
Recovery of Proteins and Microorganisms from Cultivation Media by Foam Flotation
201
Table 1. Values of m corr for biological systems and nutrient salt solution in a bubble column at
w SG = 4 cm s –1 . The reference is the nutrient salt solution with Desmophen which has the
lowest k L a value [40]
Biological system
Substrate (Antifoam)
m corr
Chaetomium cellulolyticum glucose (no antifoam)
2.56
C. cellulolyticum
glucose (small amount of Desmophen) 1.21
Escherichia coli
casein
(small amount of Desmophen) 1.40
peptone
Saccharomyces cerevisiae
glucose (small amount of Desmophen) 1.22
Hansenula polymorpha
glucose (small amount of Desmophen) 2.29
H. polymorpha
glucose (small amount of Desmophen) (with substrate
limitation 2.17)
H. polymorpha
ethanol (small amount of silicon oil)
1.52 (with oxygen
transfer limitation)
H. polymorpha
ethanol (small amount of Desmophen) 1.52 (with substrate
limitation)
Nutrient salt solution
(no antifoam)
2.29