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Biofuel Production from Carbon monoxide
Homepage1.Background2.Executive Summary3.Introduction4.Summary
4.1 Article 1 4.2 Article 25. Comparative Analysis6. References
(Background picture obtained from http://projectbiofuel.blogspot.com.au/) Next Page
1. Background
Hello everyone! My name is Geetika Kalleechurn and I am
currently doing a major in Biotechnology and Molecular
Biology.
My topic is biofuel production from acetogenic bacteria
that use carbon monoxide as a carbon source and
synthesise ethanol.
I chose this topic as I found the idea of carbon monoxide
utilization in biofuel production quite fascinating and I hope
you do too!
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Homepage
1.Background2.Executive Summary3.Introduction4.Summary
4.1 Article 4.2 Article 5. Comparative Analysis6. References
2. Executive Summary
This work involves a comparative analysis of two experiments
based on the parameters affecting the growth of acetogenic
Clostridium species that synthesise ethanol via syngas
fermentation. The aim is to understand the effects of variation
in parameters on the growth of the Clostridium species in order
to optimise ethanol production from syngas fermentation.
(Image obtained from blogs.cleanfuelsdc.org) Previous Next
Homepage
1.Background2.Executive Summary3.Introduction4.Summary
4.1 Article 4.2 Article 5. Comparative Analysis6. References
3. Introduction
With a worldwide increase in the consumption and gradual diminishing of fossil fuels, the need for renewable energy sources has also increased. Bio-fuels such as ethanol have attractive prospects in the industry. Ethanol can be produced using a series of pathways.
Figure 1 from Wei et al, 2008 shows the different pathways that can be used for ethanol production from feedstock.For the purpose of this study the main focus will be on the gasification biosynthesis pathway used by the bacterium Clostridium ljungdahlii
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Homepage
1.Background2.Executive Summary3.Introduction4.Summary
4.1 Article 4.2 Article 5. Comparative Analysis6. References
3. IntroductionCarbon monoxide is highly toxic to living creatures with the exception
of microorganisms such as acetogenic bacteria. These can use carbon
monoxide as a carbon source and synthesise ethanol and acetate
together with some other products (Kopeke et al., 2011). The
metabolic pathway used by these microorganisms is known as the
Wood-Ljungdahl pathway (shown in figure 1). The fermentation process
has a number of advantages though syngas fermentation is yet to be
used on a commercial scale. The advantages include the utilization of
the whole biomass for product formation; no pre-treatment steps
required; high specificity of biological catalysts (Munasinghe and
Khanal,2010). Nevertheless, there are also some challenges involved in
the process one of which is the poor solubility of carbon monoxide gas
in aqueous solutions (Abubackar et al., 2012)
For the purpose of this study, the activity of two Clostridium species
grown under different conditions for the optimisation of ethanol
production were compared.
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1.Background2.Executive Summary3.Introduction4.Summary
4.1 Article 14.2 Article 2
5. Comparative Analysis6. References
3. Introduction
Figure 1 adapted from Kopke et al, 2011
The Wood-Ljungdahl Pathway-Conversion of carbon monoxide to ethanol
4.1 Summary
Overview
C.ljungdahlii is an acetogenic bacteria, which, when grown on carbon monoxide produces ethanol and acetate as the
main end-products. Optimisation of ethanol production requires a shift in metabolism from acetogenesis (Acetic acid
formation) to solventogenesis (ethanol production). Resting cells have to found capable of inducing this shift in
metabolism and also increase cell stability. In this study, the ability of nitrogen-limited media to initiate a non-growing
in C.ljungdahlii and the effects of different growth states and medium pH on ethanol and acetate production were
examined.
Materials and Methods
Table 1 (Cotter et al, 2009) shows the
types of media used for C.ljungdahlii.
Three types of non-growth media
were prepared anaerobically.
The cultures were initially grown until
a mid-late log phase and then were
subjected to a series of centrifugation
and resuspension. The suspensions
were then transferred to the
appropriate non-growth media.
(material used from Cotter et al.,2009)
Ethanol and acetate production by Clostridium ljungdahlii and Clostridium autoethanogenum using resting cellsJacqueline L. Cotter , Mari S. Chinn and Amy M.Grunden
(*note for the purpose of this study the main focus will be on Clostridium ljungdahlii)
Non-growth media
4.1 Summary
Effect of non- growth media
Studies showed that the addition of vitamins, salts
and trace elements enabled the cultures to maintain high
cell densities in nitrogen deficient media. The results from
figure 1 showed that relatively few cultures from each type
of non-growth media remained viable. The ethanol
production levels were affected by the media type used.
Effect of pH on resting cell performance
It was found that lowering pH values did not affect the
stability of the culture but had an adverse effect on the
viability.
Discussion
The results obtained in this study are quite different
from studies carried out in the past whereby, ethanol
is a secondary metabolite in syngas fermentation. A shift
in metabolism as observed with other studies was not
successfully established in this experiment.
(Materials used from Cotter et al., 2009)
Results and Discussion
Figure 1 shows the metabolism of C.ljungdahlii – ethanol production over time in initial non-growth media
Figure 2 shows the metabolism of C.ljungdahlii on NG.RCM.NA.SVE medium-ethanol production over time at different pH
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1.Background2.Execuve Summary3.Introduction4.Summary 4.1 Article 1 4.2 Article 25. Comparative Analysis
6. References
4.2 Summary
Overview
Second generation biofuels such as ethanol by syngas fermentation using C.ljungdahlii
represents several challenges, one of which is the cultivation of the bacterium as it is strictly
anaerobic. The main aims of this study were to investigate and monitor the fermentation
conditions such as fresh medium flow rate, culture pH on cell concentration and viability,
substrate uptake and product formation during the continuous cultivation of C.ljungdahlii.
(*note for the purpose of this study only the results for substrate uptake and product formation
will be used)
Materials and methods
The inoculum was prepared using a defined medium containing,
NaHCO3, a reducing agent, vitamins, trace elements. The pH
of the medium was maintained at 6.8 using NaOH solution.
The bioreactor was operated under batch conditions for 3 days
following which a continuous mode was started with a liquid
flow rate of 0.25mL/min.
(note pH of bioreactor was not controlled)
Cell growth was monitored by determining
the cell dry weight of C.ljungdahlii and
acetate and ethanol production was
monitored using a gas chromatogram.
(Material used from Mohammadi et al., 2012)
Sustainable ethanol fermentation from synthesis gas by Clostridium ljungdahlii in a continuous stirred tank bioreactorMohammadi M., Younesi H., Najafpour G., Mohamed A.R.
Figure 1 shows the operating conditions of the bioreactor for optimising the liquid flow rate at a constant stirring rate of 500 rpm and a gas flow rate of 14mL/min
1.Background2.Executive Summary
3.Introduction4.Summary 4.1 Article 1 4.2 Article 25. Comparative Analysis6. References
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4.2 summary
The results for substrate uptake, product formation and varying pH were analysed.Effect of varying pH
The effect of changes in pH can be seen in Figure 2,whereby a drastic
reduction in cell density was observed due to a drop in pH to 4.18.
A re-adjustment in pH to 6.5 allowed to cells to recover within 5 days.
Product formation
From figure 3, it was observed that over the first 7 days when there was
a drop in the pH of the culture, acetate was the main product. Following this,
a drastic increase in both ethanol and acetate was observed, with the
product levels reaching a peak of 9g/L on the 10th day of the experiment.
Discussion
A decrease in pH affects the cell stability and product formation.
The production of acetate during the first 7 days led to a decrease in external pH and loss of constant
internal pH. Acetate- a weak organic acid, can accumulate inside the cells
and in the presence of H+ ions cause a decrease in internal pH. This in turn
leads a metabolic shift from acetogenesis to solventogenesis.
Hence , ethanol production occurred after a decrease in internal pH.
This study was successful in demonstrating a shift in the
metabolic pathway of C.ljungdahlii . Further studies involving
variation of other parameters are expected to help in increasing
the molar ratio of ethanol to acetate.
(Materials used from Mohammadi et al., 2012)
Results and Discussion
Figure 2 shows the change in the cell dry weight with changes in pH over time
Figure 3 shows the varying levels ethanol and acetate produced over time
5. Comparative analysis
The works from both Cotter et al. and Mohammadi et al. focused on the
production of ethanol from syngas fermentation using the bacterium Clostridium
ljungdahlii .
The studies performed in Cotter et al. were relatively complex and the goals of
the experiments performed for C.ljungdahlii were not successfully met with. The
results obtained showed were different to what was expected-ethanol was
produced in the growth phase of the bacteria while the results obtained from
other researchers showed otherwise.
The work performed by Mohammadi et al. aimed at providing a better
understanding and correlation of the biochemical pathway used by C.ljungdahlii.
The design of the experiment was far much simpler than the work that was
undertaken by Cotter et al. .
The goals of the experiment were successfully met with through the
demonstration of a shift in metabolism of the bacteria under different
parameters. The shift in metabolism from the acetogenic pathway to the
solventogenic pathway was found to correlate well with the Wood-Ljungdahl
Pathway. Furthermore , the metabolic shift was also observed in a study
performed by Gaddy et al.
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Homepage
1.Background2.Executive Summary
3.Introduction4.Summary 4.1 Article 1 4.2 Article 25. Comparative Analysis6. References
6. References1) Abubackar H.N., Veiga M.C., Kennes C., 2012. “Biological conversion of carbon
monoxide to ethanol: Effect of pH, gas pressure, reducing agent and yeast extract”,
Bioresource Technology 114:518-522
2) Cotter J.L., Chinn M.S., Grunden A.M., 2009. “Ethanol and acetate production by
Clostridium ljungdahlii and Clostridium autoethanogenum using resting cells”,
Bioprocess and Biosystems Engineering 32(3):369-380
3) Kopke M., Mihalcea C., Bromley J.C., Simpson S.D., 2011. “Fermentative
production of ethanol from carbon monoxide” Current Opinion in Biotechnology
(22)3:320-325
4)Mohammadi M., Younesi H., Najafpour G., Mohamed A.R., 2012. “Sustainable
ethanol fermentation from synthesis gas by Clostridium ljungdahlii in a continuous
stirred tank bioreactor” Journal of Chemical Technology and Biotechnology
(87)6:837-843
5)Munasinghe P.C., and Khanal S.K.,2010. “Biomass-derived syngas fermentation
into biofuels: Opportunities and challenges” Bioresource Technology (101):13 5013-
5022
6) Wei L., Pordesimo L.O., Igathinathane C., Batchelor W.D.,2008. “Process
engineering evaluation of ethanol production from wood through bioprocessing and
chemical catalysis” Biomass and Bioenergy 33:255-266
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