840.119:Hydrogen Production by Chlamydomonas reinhardtii cells in Sulfur-deprived Environments: Difference between revisions
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It has been shown that cells immobilized by culturing porous glass surfaces significantly increased the rate of reactivity. This method allows the quick and easy binding of immobilized cells to a surface. Still, this method for immobilizing the algal cells is expensive and the actual amount of immobilized culture is very low. To increase the amount of immobilized culture increased lengths of incubation time were necessary. With this method we are not able to produce molecular hydrogen in large quantities or at a low cost [4]. | It has been shown that cells immobilized by culturing porous glass surfaces significantly increased the rate of reactivity. This method allows the quick and easy binding of immobilized cells to a surface. Still, this method for immobilizing the algal cells is expensive, and the actual amount of immobilized culture is very low. To increase the amount of immobilized culture increased lengths of incubation time were necessary. With this method we are not able to produce molecular hydrogen in large quantities or at a low cost [4]. | ||
An alternative method has been developed by Laurinavichene et al. To achieve a higher concentration of immobilized cells glass fibers were placed in the media and inoculated with algae prior to cell and colony growth. This was accomplished by placing glass fibers | An alternative method has been developed by Laurinavichene et al. To achieve a higher concentration of immobilized cells glass fibers were placed in the media and inoculated with algae prior to cell and colony growth. This was accomplished by placing glass fibers in a cylinder shaped vessel along the cylindrical surface. The apparatus was then sterilized via autoclave, filled with media (Tris-acetate-phosphate (TAP)), and inoculated with algal cells. After incubation the concentration of immobilized cells was eight to ten times the concentration obtained when simply using porous glass [4]. | ||
The apparatus used to expose the cultures to light was referred to as a photobioreactor, which consisted of two glass plates bound together by clamps and grease. Each glass plate also included two inlet tubes, for argon and media exposure. Argon flow was necessary to increase the apparatus’s ability mix media that were being presented. Silicon partitions were present on the inside of the glass walls in order to direct the flow of media and argon. The matrix of glass fibers previously described was placed between the two plates of the apparatus. The photobioreactor was then filled with the media TAP. After two to five days the media with low sulfate (sulfur) concentrations was introduced along with argon bubbling to allow the mixture of the liquid media. The entire apparatus was also exposed to cool florescent light. | The apparatus used to expose the cultures to light was referred to as a photobioreactor, which consisted of two glass plates bound together by clamps and grease. Each glass plate also included two inlet tubes, for argon and media exposure. Argon flow was necessary to increase the apparatus’s ability to mix media that were being presented. Silicon partitions were present on the inside of the glass walls in order to direct the flow of media and argon. The matrix of glass fibers previously described was placed between the two plates of the apparatus. The photobioreactor was then filled with the media TAP. After two to five days the media with low sulfate (sulfur) concentrations was introduced along with argon bubbling to allow the mixture of the liquid media. The entire apparatus was also exposed to cool florescent light. | ||
The concentration of algal chlorophyll (a and b) was measured by using extraction with an ethanol solvent. A technique that could indicate the ability for the culture to make successive amounts of molecular hydrogen, | The concentration of algal chlorophyll (a and b) was measured by using extraction with an ethanol solvent. A technique that could indicate the ability for the culture to make successive amounts of molecular hydrogen, and if the concentration of chlorophyll was low, we could then change the media to a sulfate rich (high sulfur concentration) media, in order to regenerate the cells’ ability to make molecular hydrogen. By running ethanol extractions on the media output we could also determine the amount of culture that was coming out with the output media. This would be an indicator of the cells’ ability to bind to our matrix, and how this ability changed over time or media exposure. | ||
Gas chromatography was performed on the gaseous output in order to measure the concentrations of molecular hydrogen and oxygen produced in the photobioreactor. | Gas chromatography was performed on the gaseous output in order to measure the concentrations of molecular hydrogen and oxygen produced in the photobioreactor. | ||
A schematic of the photobioreactor is shown below. | A schematic of the photobioreactor is shown below. | ||
====[[Image:schematic.jpg]]==== | ====[[Image:schematic.jpg]]==== | ||
Revision as of 12:43, 25 November 2006
Hydrogen Production by Chlamydomonas reinhardtii cells in Sulfur-deprived Environments
Abstract
Many recent developments have been made in the research of Chlamydomonas reinhardtii for hydrogen production. The purpose of this webpage is to assist in understanding the recent developments being written about in academic journals regarding hydrogen production, and to help clarify the idea of using a biological organism to produce hydrogen for energy use.
State of the Art
State of hydrogen production and utilization
The main reason why many are looking at hydrogen fuel for energy is to curb the worldwide use of crude oil to produce fuel for vehicles. The molecular hydrogen would combine with molecular oxygen and produce water as a byproduct. The use of hydrogen in vehicles is currently being researched by major car companies, and many are confident that hydrogen fuel will be utilized in vehicles.[5]
The problem of crude oil supplies, cost, and availablity will get worse as other countries around the world become more industrialized and need oil-consuming vehicles like the United States. Currently, as of 2006, 97% of fuel used for transportation comes from crude oil.[5]
The vast majority of molecular hydrogen is currently made by a process that heats up petroleum and natural gas to high temperatures. Producing hydrogen using crude oil defeats the purpose of using hydrogen as a clean alternative fuel to gasoline although on a small scale, using only natural gas to produce hydrogen would result in half as much carbon emissions as using current gasoline for cars. The other ways of producing hydrogen gas is the electrolysis of water (running electricity through water to split the water into hydrogen and oxygen) using electricity produced from wind, solar, or hydroelectric generators. The main problem with electrolysis is that humans need electricity, and some electricity is still made from fossil fuels. Therefore, more electricity would need to be produced from fossil fuels if electricity from renewable energy is used for hydrogen production.[5]
The main objective of the current research is lowering the cost of the hydrogen produced by the Chlamydomonas reinhardtii. These objectives have been outlined below:
- Increasing the hydrogen production yield per gram of organism.
- The long recovery time between switching the Chlamydomonas reinhardtii from sulfur deprived to sulfur replete conditions.
- Current expense of the reactor material.[2]
State of Chlamydomonas reinhardtii research
Many articles have been written about the ability to produce hydrogen from green algae, and this has been known about for over 60 years [1]. The state of Chlamydomonas reinhardtii research is making hydrogen production more efficient and less expensive.
Objectives
The main objective of this website is to review current trends in microbial hydrogen production research by specifically focusing on recent research in molecular hydrogen production by Chlamydomonas reinhardtii in sulfur deprived media. We will accomplish this by providing background information in molecular hydrogen production followed by explaining the mechanisms by which hydrogen is produced in the green algea, Chlamydomonas reinhardtii, and some techniques in which molecular hydrogen is extracted will also be explained.
Scientific Approach
Background
Some forms of green algea can produce molecular hydrogen gas utilizing the near infrared region of sunlight using the [Fe]-hydrogenase. The [Fe]-hydrogenase enzymes in Chlamydomonas reinhardtii absorb light from 400-700nm with a light conversion to hydrogen of 13 to 15%. The formation of hydrogen can be simplified as 2H+ + 2FD- -> H2 + 2FD, where the FD is the main [Fe]-hydrogenase enzyme that produces the molecular hydrogen.
Chlamydomonas reinhardtii alone
Chlamydomonas reinhardtii is put in an oxygen deprived environment. If molecular oxygen is present, the pathway for hydrogen production is irreversibly inhibited [1]. The deprivation of sulfur acts as a metabolic switch between oxygen production (sulfur present), which require oxygen scavengers that are componds or organisms that adsorb all molecular oxygen that is present in order to prevent the irreversibly inhibited hydrogen production and hydrogen production (no sulfur)[3]. The absence of sulfur then expressess the hydrogenase enzyme, which will use both water oxidation, and catabolism of starch to produce molecular hydrogen in an acidic environment. Without an acidic environment, which is done by adding acetic acid, the molecular hydrogen will not be produced.
Immobilization
The immobilization of Chlamydomonas reinhardtii cells in our culture under study allowed the cells to be easily separated from the liquid phase as opposed to allowing the algae to remain suspended in the liquid media. If we are able to prevent the cells from becoming suspended in the liquid solution, we would then be able to exchange sulfate deficient (low sulfur concentration) media for sulfate rich media in a more efficient and economically feasible manner. Though hydrogen production is optimized in sulfur-depleted conditions, it is still necessary to expose the culture to a media rich in sulfur to regenerate the algal culture's ability to produce molecular hydrogen (this allows our samples to be recycled). Aside from the increased ability to exchange sulfur-rich and sulfur-deficient media, another advantage of cell immobilization is the capability to concentrate our culture without losing the cells’ ability to be exposed to light [4].
Techniques
It has been shown that cells immobilized by culturing porous glass surfaces significantly increased the rate of reactivity. This method allows the quick and easy binding of immobilized cells to a surface. Still, this method for immobilizing the algal cells is expensive, and the actual amount of immobilized culture is very low. To increase the amount of immobilized culture increased lengths of incubation time were necessary. With this method we are not able to produce molecular hydrogen in large quantities or at a low cost [4].
An alternative method has been developed by Laurinavichene et al. To achieve a higher concentration of immobilized cells glass fibers were placed in the media and inoculated with algae prior to cell and colony growth. This was accomplished by placing glass fibers in a cylinder shaped vessel along the cylindrical surface. The apparatus was then sterilized via autoclave, filled with media (Tris-acetate-phosphate (TAP)), and inoculated with algal cells. After incubation the concentration of immobilized cells was eight to ten times the concentration obtained when simply using porous glass [4].
The apparatus used to expose the cultures to light was referred to as a photobioreactor, which consisted of two glass plates bound together by clamps and grease. Each glass plate also included two inlet tubes, for argon and media exposure. Argon flow was necessary to increase the apparatus’s ability to mix media that were being presented. Silicon partitions were present on the inside of the glass walls in order to direct the flow of media and argon. The matrix of glass fibers previously described was placed between the two plates of the apparatus. The photobioreactor was then filled with the media TAP. After two to five days the media with low sulfate (sulfur) concentrations was introduced along with argon bubbling to allow the mixture of the liquid media. The entire apparatus was also exposed to cool florescent light.
The concentration of algal chlorophyll (a and b) was measured by using extraction with an ethanol solvent. A technique that could indicate the ability for the culture to make successive amounts of molecular hydrogen, and if the concentration of chlorophyll was low, we could then change the media to a sulfate rich (high sulfur concentration) media, in order to regenerate the cells’ ability to make molecular hydrogen. By running ethanol extractions on the media output we could also determine the amount of culture that was coming out with the output media. This would be an indicator of the cells’ ability to bind to our matrix, and how this ability changed over time or media exposure.
Gas chromatography was performed on the gaseous output in order to measure the concentrations of molecular hydrogen and oxygen produced in the photobioreactor.
A schematic of the photobioreactor is shown below.
Potential Impact
The potential impact of producing hydrogen by organism who utilize the sunlight to produce hydrogen is unmeasurable. If hydrogen is able to be made via the Chlamydomonas reinhardtii organism (or others) on an economically competitive level as fossil fuel or electrical hydrogen production then the world would use far less carbon based fuel for energy needs.
Associated Risks
The risks involved with the project have to deal with taking adequate precautions, since molecular hydrogen is prone to explosions. In order for the hydrogen production to be useful to humankind a large amount of hydrogen would need to be produced at one place for shipment. Therefore, it proper precautions would be manditory to ensure no hydrogen explosions at the hydrogen production plant. With mass production of Chlamydomonas reinhardtii it would be necessary to ensure no mass dumping of unused algae into local lakes or ponds to ensure the aquatic life would survive near a plant making hydrogen from algea.
Ethical Issues
Currently their is no ethical issues with using algae for hydrogen production, which is one of the main benefits of using Chlamydomonas reinhardtii.
References
[1] Tsygankov, A et al. "Hydrogen Production by Sulfur-deprived Chlamydomonas reinhardtii under Photoautotrophic Conditions." International Journal of Hydrogen Energy. 2006;31:1574-1584.
[2] Amos, W. and M. Ghirardi. "Renewable Hydrogen from Green Algae." Biocycle Energy. 2004;May:59 and 62.
[3] Melis, A. and M. Melnicki. "Integrated Biological Hydrogen Production." International Journal of Hydrogen Energy. 2006;31:1563-1573.
[4]
[5] Ogden, Joan. "High Hopes for Hydrogen." Scientific American. 2006;Sept295:i3:94-101.
