This study investigated using anaerobic fermentation by bacteria on pretreated biomass to produce biofuel. The hypothesis was that a co-culture of two bacterial strains would yield the highest percentage of ethanol. Two bacterial strains (Clostridium Thermocellum and Clostridium Thermolactium) and a co-culture were studied. Results showed the co-culture produced the highest level of ethanol at 14.55% on average, validating the hypothesis. Single strains also effectively produced ethanol, with Clostridium Thermocellum yielding more than Clostridium Thermolactium. Bacterial fermentation was found to be a viable option for large-scale biofuel production.
3. Hypothesis
If compared with last year’s study of
enzymatic hydrolysis, single-strain
bacterial cellulose hydrolysis will be
proven to produce more ethanol;
whereas combining two strains of
bacteria in a co-culture will yield the
highest percentage of ethanol.
4. Controls
The tools, equipment, materials, and
procedures were identical within each
of the three groups studied
The two different bacteria strains and
the co-culture were the variables
Variables
6. Collect and
Dry Materials
Grind, Detoxify
and Neutralize
Recover and
Measure
Ethanol
Graphical
Analysis
Bacterial Hydrolysis
Fermentation of
Sugars
No
Pretreatment
Acid
Pretreatment
Co-Culture
Media and
Autoclave
Clostridium
Thermolactium
Clostridium
Thermocellum
Corn Stover
7.
8.
9. Glucose and Xylose Percentages
Treated Sample
One
Treated Sample
Two
Untreated
Sample One
Untreated
Sample Two
Glucose
Percentage
48.4 49.2 33.1 33.8
Xylose
Percentage
17.3 19.1 16.3 13.5
Average
Percentage
Glucose
48.8 33.5
Average
Percentage
Xylose
18.2 14.9
10. Where:
mpaper+lignin = Oven dry weight of filter paper and lignin, mg
mpaper = Oven dry weight of filter paper, mg
msample = Oven dry weight of sample, mg
12. Basal Medium
Chemical Formula Required Grams (g)
Sodium Chloride NaCl 10.000
Magnesium MgCl2.6H2O 0.500
Potassium Dihydrogen
Phosphate
KH2PO4
0.200
Ammonium Chloride NH4Cl 0.300
Potassium Chloride KCl 0.300
Calcium Chloride Hydrate
2X with Water
CaCl2 2H2O
0.015
Sodium Bicarbonate NaHCO3 2.520
Resazurin 0.050
Yeast extract 4.000
L-Cysteine 0.240
13.
14.
15. Results
Based on high ethanol content, it
was concluded that the most viable
choice for large-scale production
was the co-culture
Clostridium Thermocellum produced
more ethanol than Clostridium
Thermolactium in the single-strain
trials
16. HPLC Results – Ethanol Content – Ethanol Average
Bacteria
Ethanol, ml
ethanol per ml
of solution
Ethanol,
% v/v
Average
Ethanol %
(a,b,c)
v/v
Clostridium
Thermocellum 1a 0.0720 7.20 7.18
1b 0.0545 5.45
1c 0.0890 8.90
Control 1d 0.0025 0.25
Control 1e*
Clostridium
Thermolactium 2a 0.0435 4.35 5.08
2b 0.0410 4.10
2c 0.0680 6.80
Control 2d 0.0012 0.12
Control 2e*
Co-culture 3a 0.1705 17.05 14.55
3b 0.1225 12.25
3c 0.1435 14.35
Control 3d 0.0210 2.10
Control 3e 0.0180 1.80
* The label "*" control samples couldn't give integratable HPLC curves, probably they were too
small, and were covered by noisy signals.
18. Comparison of Enzymatic Hydrolysis (2012) and Bacterial Hydrolysis (2013)
Enzymatic Hydrolysis Bacterial Cellulose Hydrolysis
Biomass
(2011-2112)
NaOH Pretreatment
Average Ethanol %
(a and b)
v/v
(2011-2012)
H2SO4 Pretreatment
Average Ethanol %
(a and b)
v/v
(2012-2013)
Clostridium
Thermocellum
Average Ethanol %
(a,b,c)
v/v
(2012-2013)
Clostridium
Thermolactium
Average Ethanol %
(a,b,c)
v/v
(2012-2013)
Co-culture
Average Ethanol %
(a,b,c)
v/v
Corn
Stover 5.135 8.994 7.18 5.08 14.55
Figure A11: Comparison of Ethanol Content 2012 and 2013
Comparison of Ethanol Content 2012 and 2013
20. Acknowledgments
I thank Dr. Ulrike Tschirner, from the
University of Minnesota, for her generous
and steadfast assistance with equipment
and materials, with bacteria, and with
informed counsel.
Editor's Notes
Title PageThe essential purpose of this research was to discover a new approach to realize a superior yield when producing Cellulosic ethanol. Cellulosic biofuel is attractive because, rather than utilize food crops, such as corn, it transforms farm waste into a renewable and clean-burning biofuel. The current method using enzymatic hydrolysis to release sugars followed by a separate yeast fermentation has made biofuel production profitable and reduced gas prices at the pump by as much as $1.09 in 2012. However, this requires a two-step process and can only effectively ferment glucose, whereas bacterial hydrolysis releases both glucose and xylose from the biomass and ferments it all in one step.By using two bacteria strains that efficiently degrade different sugars, I thought to increase the ethanol yield, and this proved to be true. The co-culture that I evaluated for this study dramatically increased ethanol yield.
Here are the things we will be covering.
HypothesisI believed that bacteria would produce more ethanol than enzymes and that the co-culture, using equal portions of the two bacteria, would be the most efficient of the processes. This was based on information about the two bacteria strains that were used in this study. The first, Clostridium Thermocellum efficiently degrades hexoses, monosaccharides with six carbon atoms, while the second, Clostridium thermolactium proficiently degrades pentoses, monosaccharides with five carbon atoms. Therefore, I expected the co-culture to convert most of the sugars and produce the highest percentage of ethanol.
Controls and VariablesThese things were all identical in each experiment.The bacteria strains were the variables
Bacteria StudiedHere you see the three bacteria strains I testedThe co-culture contained equal part of Clostridium Thermocellum and Clostridium thermolactium
Project Flow ChartHere is a flowchart showing the process I followed.
Grinding Biomass and Acid PretreatmentThe biomass was cut, dehydrated, and then ground to the size of 50-micron particlesAfter pretreating the biomass with a 1% sulfuric acid solution under pressure and at 120-degrees Celsius to break down the lignin and release the sugars, I washed it to a pH of seven.
Determination of Klason LigninHere is the filtrate in the back with the Klason Lignin on the filters in front.
Sugar ContentTo determine the percentages of glucose and xylose, I analyzed the filtrate using high-performance liquid chromatography - you see the results here
Formula to Determine Klason ContentThe Klason Lignin content was determined using this formula.
Klason Lignin content in table
Basal MediaAll of the processes undertaken up to this point have been to analyze the biomass. Understanding the composition of the biomass is vital to designing the perfect method of pretreatment, hydrolysis and fermentation that will lead to production of the highest ethanol yield in the most cost-effective and sustainable system.Now I was able to begin the bacterial hydrolysis process.First, I created the basal medium using this list of components
Introducing Bacteria into MediaUtilizing a precise scale, I isolated fifteen, .002-gram specimens of biomass and placed them in 15, ten-mL, sterile serum bottles, I added five milliliter’s of the basal media to each bottle and boiled them to remove the oxygen – point to resazurin – the oxygen indicator, Resazurin, in the media changes from a rose color to very pale yellow when the oxygen has been depleted from the media Next, I autoclaved the samples for 20 minutes at 20 pounds per square inch and 121 degrees Celsius to remove all undesirable organismsMy next step was to create the perfect environment for the bacteria to thrive by adding the following four solutions - Point to table of added solutions -Trace Element SolutionSelenium - Tungstate solutionVitamin SolutionSodium Sulfide Solution-to remove the remaining oxygen Now I was ready to introduce the bacteria – utilizing a hypodermic syringe, I added .5 ml of Clostridium thermocellum to five samples, .5 ml of Clostridium thermolactium to another five samples, and .25 ml of each (creating a co-culture)to the last five
Incubating Bacteria and Biomass Then I placed the bottles in the incubator at 60 degrees Celsius for five days to create the optimal environment to facilitate effective bacterial hydrolysis and fermentation of the sugars The last step was determining ethanol percentages through use of the High-Performance Liquid Chromatography (HPLC)To do this, I calibrated the HPLC by running pure ` samples of ethanolThe biomass samples were then filtered and placed in the HPLC at specific locations that identified them by material and as “a”, “b”, or “c” “d” or “e” samples; and processed to determine the ethanol content.This was a long process, taking about sixty hours to complete each test.
After examining the results of the bacteria strains tested, it was concluded that the most advantageous bacteria choice for large-scale ethanol production was the co-culture. This was based on high ethanol content.
Results Table and GraphThe five samples of the Clostridium thermolactium strain performed poorly, producing less ethanol than either the Clostridium thermocellum or the co-culture. However, when the two strains were combined in the co-culture, there was a dramatic increase in fermented sugars that surpassed any method previously tested.
Chart Showing Ethanol Percentages – Bacterial Hydrolysis and FermentationSo, after analyzing the test results, it was clear that anaerobic fermentation using a co-culture is a feasible method of producing ethanol.
Comparison of Enzymatic Hydrolysis 2012 and Bacterial Hydrolysis 2013Here is a comparison of last year’s trials with enzymatic hydrolysis with its separate yeast fermentation and this year’s study of the one-step bacterial hydrolysis and fermentation.
The comparison illustrated in a bar graph.
I thank Dr. Ulrike Tschirner, from the University of Minnesota, for her generous and steadfast assistance with equipment and materials, with bacteria, and with informed counsel.