Cofermentation as efficient tool for the production of
ethanol from pentoses and hexoses
M. Monzón Lozano, S. Poth, N. Tippkötter, R. Ulber
TU Kaiserslautern, Institute of Bioprocess Engineering, Gottlieb-Daimler-Straße 44, 67663 Kaiserslautern
1. Introduction
Production of ethanol biofuel from renewable resources such as lignocellulose, promises to be an innovative approach to replace
fossil fuels in the future. Furthermore its use contributes to the environment protection by reducing the accumulation of CO2 in the
atmosphere. Lignocellulosic materials like wood consist of three main components, celluloses (40-50%), hemicelluloses (20-35%)
and lignin (20-30%). Celluloses are composed of glucose monomers and xylose is the major sugar monomer present in the
hemicellulose fraction. These sugar monomers are released by enzymatic hydrolysis of lignocellulose. A great number of
Fermentation of
released
sugar monomers
from hydrolysate
microorganisms can ferment glucose to ethanol, but only a few microorganisms
can
metabolize
xylose to ethanol
at significantly
yields. Xylose is the second most abundant sugar available in lignocellulosic biomass and therefore an appropriate selection of
microorganisms for an efficient fermentation process is required.
2. Selection of appropriate microorganisms
3. Fermentation experiments on different substrates
Aim of these experiments was to select the best appropriate
microorganisms able to use xylose as well as glucose for the
production of high ethanol amounts.
In following experiments co-fermentations in shake flakes
with the selected yeasts were performed.
0,4
Yie ld s o n Su b s tra t [g /g ]
Substrate
xylose+glucose
Yeast A +
S.cerevisiae
xylose+glucose
Yeast A
EtO H
0,35
EtO H
0,3
0,25
EtO H
0,2
0,15
0,1
CDM
0,05
CDM
CDM
0
M ode l substrate s
(xyl+ glu)
0
4
8
12
16
Ratio EtOH/Substrate [%]
20
24
Fig. 1: Microorganisms selection for EtOH production
(Cultivation conditions: 30 °C, 50 ml, 130 rpm, 24 h, Inoculum: 10% of working volumen)
In Fig. 1 are shown the results of two tested microorganisms
Saccharomyces cerevisiae and another yeast using a complex
medium with the tested substrates xylose or xylose and
glucose. The highest ethanol concentration was achieved
with a co-culture of the two yeasts.
4. Scale up experiments in biofermenters
Fermentations for scale up
were performed in reactors
with 4l working volumen,
using a minimal medium. The
obtained yield of EtOH (0,45
g/g) by the fermentation with
glucose as model substrate
reached nearly the value of
the max. theoretical EtOH
Fig. 3: Bioreactors for Scale up experiments
yield (0,51 g/g).
On hydrolysates a slightly lower yield of approx. 0,3 g/g
was reached.
The work is funded by:
Förderkennzeichen:
22027405
http://www.mv.uni-kl.de/biovt
H ydrolyse d ce llulosic
fraction
H e mice llulosic fraction
Fig. 2 Fermentation using different substrates
(Cultivation conditions: 30 °C, 100 ml, 130 rpm, 24 h, Inoculum: 10% of working volumen)
Fig. 2 shows the obtained yields on different substrates by
co-fermentation of yeasts in shake flasks. The medium
contained only (NH4)2SO4 as N-source, trace elements and
vitamins. Similar yields could be reached by the
fermentation of xylose and glucose and hydrolysed
cellulosic fraction coming from wooden feedstock. Using
the hemicellulosic substrate, ethanol production was also
possible but the obtained yields were lower.
5. Increasing the final ethanol concentration
Since a higher ethanol concentration as in the performed batch cultivations is
preferable, fed-batch experiments were carried out in the
reactors mentioned above.
The aime to increase the
ethanol concentration could
be reached by feeding a
glucose solution after 18 h of
fermentation. After another 54
h of feeding glucose a nearly
ten fold higher ethanol concentration could be reached.
55
50
Ethanolconcentration [g/L]
xylose
45
40
35
30
25
20
15
10
5
0
18
72
time [h]
Fig. 2 Ethanol concentration after
fed-batch cultivation
(Cultivation conditions: 30 °C, 100 ml, 130 rpm, 24 h,
Inoculum: 10% of working volumen)
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