Biohydrogen

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Microbial hydrogen production.

Biohydrogen is defined as hydrogen produced biologically, most commonly by algae and bacteria. Biohydrogen is a potential biofuel obtainable from both cultivation and waste organic materials.[1]

Contents

[edit] Introduction

Currently, there is a huge demand of the chemical hydrogen. There is no log on the production volume and use of hydrogen world-wide. However the estimated consumption of hydrogen is expected to reach 900 billion cubic meters in 2011[2]

Refineries are large-volume producers and consumers of hydrogen. Today 96% of all hydrogen is derived from fossil fuels, with 48% from natural gas, 30% from hydrocarbons, 18% from coal and about 4% from electrolysis. Oil-sands processing, gas-to-liquids and coal gasification projects that are ongoing, require a huge amount of hydrogen and is expected to boost the requirement significantly within the next few years. Environmental regulations implemented in most countries, increase the hydrogen requirement at refineries for gas-line and diesel desulfurization[2][3]

An important future application of hydrogen could be as an alternative for fossil fuels, once the oil deposits are depleted.[4] This application is however dependent on the development of storage techniques to enable proper storage, distribution and combustion of hydrogen.[4] If the cost of hydrogen production, distribution, and end-user technologies decreases, hydrogen as a fuel could be entering the market in 2020.[5]

Industrial fermentation of hydrogen, or whole-cell catalysis, requires a limited amount of energy, since fission of water is achieved with whole cell catalysis, to lower the activation energy.[6] This allows hydrogen to be produced from any organic material that can be derived through whole cell catalysis since this process does not depend on the energy of substrate.

[edit] Algaeic biohydrogen

Further information: Biohydrogen reactor

In 1939 a German researcher named Hans Gaffron, while working at the University of Chicago, observed that the algae he was studying, Chlamydomonas reinhardtii (a green-algae), would sometimes switch from the production of oxygen to the production of hydrogen.[7] Gaffron never discovered the cause for this change and for many years other scientists failed in their attempts at its discovery. In the late 1990s professor Anastasios Melis a researcher at the University of California at Berkeley discovered that if the algae culture medium is deprived of sulfur it will switch from the production of oxygen (normal photosynthesis), to the production of hydrogen. He found that the enzyme responsible for this reaction is hydrogenase, but that the hydrogenase lost this function in the presence of oxygen. Melis found that depleting the amount of sulfur available to the algae interrupted its internal oxygen flow, allowing the hydrogenase an environment in which it can react, causing the algae to produce hydrogen.[8] Chlamydomonas moewusii is also a good strain for the production of hydrogen. Scientists at the U.S. Department of Energy’s Argonne National Laboratory are currently trying to find a way to take the part of the hydrogenase enzyme that creates the hydrogen gas and introduce it into the photosynthesis process. The result would be a large amount of hydrogen gas, possibly on par with the amount of oxygen created.[9][10]

It would take about 25,000 square kilometres to be sufficient to displace gasoline use in the US. To put this in perspective, this area represents approximately 10% of the area devoted to growing soya in the US.[11] The US Department of Energy has targeted a selling price of $2.60 / kg as a goal for making renewable hydrogen economically viable. 1 kg is approximately the energy equivalent to a gallon of gasoline. To achieve this, the efficiency of light-to-hydrogen conversion must reach 10% while current efficiency is only 1% and selling price is estimated at $13.53 / kg.[12] According to the DOE cost estimate, for a refueling station to supply 100 cars per day, it would need 300 kg. With current technology, a 300 kg per day stand-alone system will require 110,000 m2 of pond area, 0.2 g/l cell concentration, a truncated antennae mutant and 10 cm pond depth.[13] Areas of research to increase efficiency include developing oxygen-tolerant FeFe-hydrogenases[14] and increased hydrogen production rates through improved electron transfer.[15]

[edit] Bacterial biohydrogen

[edit] Process requirements

If hydrogen by fermentation is to be introduced as an industry, the fermentation process will be dependent on organic acids as substrate for photo-fermentation. The organic acids are necessary for high hydrogen production rates.[6][16]

The organic acids can be derived from any organic material source such as sewage waste waters or agricultural wastes.[16] The most important organic acids are acetic acid (HAc), butyric acid (HBc) and propionic acid (HPc). A huge advantage is that production of hydrogen by fermentation does not require glucose as substrate.[16]

The fermentation of hydrogen has to be a continuous fermentation process, in order sustain high production rates, since the amount of time for the fermentation to enter high production rates are in days.[6]

[edit] Fermentation

Several strategies for the production of hydrogen by fermentation in lab-scale have been found in literature. However no strategies for industrial-scale productions have been found. In order to define a industrial-scale production, the information from lab-scale experiments has been scaled to an industrial-size production on a theoretical basis. In general, the method of hydrogen fermentation is referred to in three main categories. The first category is dark-fermentation, which is fermentation which does not involve light. The second category is photo-fermentation, which is fermentation which requires light as the source of energy. The third is combined-fermentation, which refers to the two fermentations combined.

[edit] Dark-fermentation

There are several bacteria with a potential for hydrogen production. The Gram-positive bacteria of the Clostridium genus, is promising because it has a natural high hydrogen production rate. In addition, it is fast growing and capable of forming spores, which make the bacteria easy to handle in industrial application.[17]

Species of the Clostridium genus allow hydrogen production in mixed cultures, under mesophilic or thermophilic conditions within a pH range of 5.0 to 6.5.[17] Dark-fermentation with mixed cultures seems promising since a mixed bacterial environment within the fermenter, allows cooperation of different species to efficiently degrade and convert organic waste materials into hydrogen, accompanied by the formation of organic acids.[17]

For the fermentation to be sustainable in industrial-scale, we[who?] need to be able to control the bacterial environment inside the fermenter. If the fermentation process is feed with sugar waste, we have a risk, that the feed will contain micro-organisms, which could change the bacterial environment inside the fermenter.[18] A way to prevent harmful micro-organisms from gaining control of the bacterial environment inside the fermenter could be through addition of probiotics which favors or promotes the intended bacterial environment and prevents harmful micro-organisms from gaining control of the fermenter.[18]

The dilution rate has to ensure that the amount of biomass inside the fermenter is stable and that the organic acids are removed properly with the outlet stream. The organic acids are toxic to the bacteria and huge amounts will interrupted the fermentation process.[17] This fermentation of hydrogen is accompanied production of carbon-dioxide which can be separated from hydrogen with a passive separation process.[19]

The fermentation will convert some of the sugar waste into biomass instead of hydrogen.[17] The biomass is however a carbohydrate-rich by-product which can be fed back into the fermenter, to ensure that the process is sustainable.[20] Fermentation of hydrogen by dark-fermentation is restricted by incomplete degradation of organic material, into organic acids and this is why we need the photo-fermentation.[17]

The separation of organic acids from biomass in the outlet stream can be done with a settler tank in the outlet stream, where the sludge (biomass) is pumped back into the fermenter to increase the rate of hydrogen production.[20]

[edit] Photo-fermentation

Photo-fermentation refers to the method of fermentation where light is required as the source of energy. This fermentation relies on photosynthesis to maintain the cellular energy levels. Fermentation by photosynthesis compared to other fermentations has the advantage of light as the source of energy instead of sugar. Sugars are usually available in limited quantities.

All plants, algae and some bacteria are capable of utilizing light as the source of energy. Cyanobacteria is frequently mentioned capable of hydrogen production by photosynthesis.[21] However the purple non-sulphur (PNS) bacteria genus Rhodobacter, holds significant promise for the production of hydrogen by fermentation.[6]

Studies have shown that Rhodobacter sphaeroides is highly capable of hydrogen production while feeding on organic acids, consuming 98% to 99% of the organic acids during hydrogen production.[6]

As for the dark-fermentation the separation of biomass can be done with a settler tank in the outlet stream, where the sludge (biomass) is pumped back into the fermenter to increase the rate of hydrogen production .[20]

Currently there is limited experience with photo-fermentation at industrial-scale. Photo-fermentation require light in the ultra-violet (UV) range up to 400 nm.[22] The distribution of light within the industrial scale photo-fermenter has to be designed to prevent self-shading inside the fermenter and to ensure sustainable hydrogen production.

A method to ensure proper light distribution and limit self-shading within the fermenter, could be to distribute the light with an optic fiber where light is transferred into the fermenter and distributed from within the fermenter.[23] Photo-fermentation with Rhodobacter sphaeroides require mesophilic conditions.[24] The optic fiber will transfer light and thus heat into the fermenter, but the heat transferred is limited.[23]

The design with an ultra-violet light-source has a huge advantage to other fermentations since ultra-violet light has the potential to eliminate foreign micro-organisms and to prevent contamination. This will limit the need of cleaning procedures. However the production rates with photo-fermentation is not as high as with dark-fermentation.

[edit] Combined fermentation

Combining dark- and photo-fermentation has shown to be the most efficient method to produce hydrogen through fermentation.[25] The combined fermentation allows the organic acids produced during dark-fermentation of waste materials, to be used as substrate in the photo-fermentation process.[6] Many independent studies show this tehcnique to be effective and practical.[26]

For industrial fermentation of hydrogen to be economical feasible, by-products of the fermentation process has to be minimized. Combined fermentation has the unique advantage of allowing reuse of the otherwise useless chemical, organic acids, through photosynthesis.

As the method for hydrogen production, this method currently holds significant promise.[6]

[edit] Metabolic processes

The metabolic process for hydrogen production are dependent on the reduction of the metabolite ferredoxin.[27]

4H+ + ferredoxin(ox) → ferredoxin(red) + 2 H2

For this process to run, ferredoxin has to be recycled through oxidation. The recycling process is dependent on the transfer of electrons from nicotinamide adenine dinucleotide (NADH) to ferredoxin.[27]

2 ferredoxin(red) + 2 NADH → 2 ferredoxin(ox) + H2

The enzymes that catalyse this recycling process are referred to as hydrogen-forming enzymes and have complex metalloclusters in their active site and require several maturation proteins to attain their active form.[27] The hydrogen-forming enzymes are inactivated by molecular oxygen and must be separated from oxygen, to produce hydrogen.[27]

The three main classes of hydrogen-forming enzymes are [FeFe]-hydrogenase, [NiFe]-hydrogenase and nitrogenase.[27] These enzymes behave differently in dark-fermentation with Clostridium and photo-fermentation with Rhodobacter. The interplay of these enzymes are the key in hydrogen production by fermentation.

[edit] Clostridium

The interplay of the hydrogen-forming enzymes in Clostridium is unique with little or no involvement of nitrogenase. The hydrogen production in this bacteria is mostly due to [FeFe]-hydrogenase, which activity is a hundred times higher than [NiFe]-hydrogenase and a thousand times higher than nitrogenase. [FeFe]-hydrogenase has a Fe-Fe catalytic core with a variety of electron donors and acceptors.[6][27]

The enzyme [NiFe]-hydrogenase in Clostridium, catalyse a reversible oxidation of hydrogen. [NiFe]-hydrogenase is responsible for hydrogen uptake, utilizing the electrons from hydrogen for cellular maintenance.[27]

In Clostridium, glucose is broken down into pyruvate and nicotinamide adenine dicleotide (NADH). The formed pyruvate is then further converted to acetyl-CoA and hydrogen by pyruvate ferredoxin oxidoreductase with the reduction of ferredoxin.[27] Acetyl-CoA is then converted to acetate, butyrate and propionate.[27][28]

Acetate fermentation processes are well understood and have a maximum yield of 4 mol hydrogen pr. mol glucose.[6] The yield of hydrogen from the conversion of acetyl-CoA to butyrate, has half the yield as the conversion to acetate.[6][27] In mixed cultures of Clostridium the reaction is a combined production of acetate, butyrate and propionate.[25] The organic acids which are the by-product of fermentation with Clostridium, can be further processed as substrate for hydrogen production with Rhodobacter.

[edit] Rhodobacter

The purple non-sulphur bacteria Rhodobacter spharoids is able to produce hydrogen from organic acids and ultra-violet light.[27] The photo-system required for hydrogen production in Rhodobacter (PS-I), differ from its oxygenic photosystem (PS-II) due to the requirement of organic acids and the inability to oxidize water.[27]

In Rhodobacter, the hydrogen production is due to catalysis by nitrogenase. The production of hydrogen by [FeFe]-hydrogenase is less than 10 times the hydrogen uptake by [NiFe]-hydrogenase.[29]

The interplay of hydrogenase and nitrogenase in this bacteria is responsible for the production of hydrogen and require nitrogen-deficient conditions to produce hydrogen.[27][29]

Rhodobacter hydrogen metabolism

The main photosynthetic membrane complex is PS-I which accounts for most of the light-harvest. The photosynthetic membrane complex PS-II produces oxygen, which inhibit hydrogen production and thus low partial pressures of oxygen most be sustained during fermentation.[27]

To attain high production rates of hydrogen, the hydrogen production by nitrogenase has to exceed the hydrogen uptake by hydrogenase.[29] The substrate is oxidized through the tricarboxylic acids circle and the produced electrons are transferred to the nitrogenase catalysed reduction of protons to hydrogen, through the electron transport chain.[27][29]

[edit] LED-fermenter

A cheap way to build a industrial-size photo-fermenter could be to build a fermenter with ultra-violet light emitting diodes (UV-LED) as light source. This design prevents self-shading within the fermenter, require limited energy to maintain photosynthesis and has very low installation costs. This design would also allow cheap models to be built for educational purpose[citation needed].

[edit] Metabolic engineering

There is a huge potential for improving hydrogen yield by metabolic engineering. The bacteria Clostridium could be improved for hydrogen production by disabling the uptake hydrogenase, or disabling the oxygen system. This will make the hydrogen production robust and increase the hydrogen yield in the dark-fermentation step.

The photo-fermentation step with Rhodobacter, is the step which is likely to gain the most from metabolic engineering. An option could be to disable the uptake-hydrogenase or to disable the photosynthetic membrane system II (PS-II). Another improvement could be to decrease the expression of pigments, which shields of the photo-system.

[edit] See also

[edit] References

  1. ^ Demirbas, A. (2009). Biohydrogen: For Future Engine Fuel Demands. Trabzon: Springer. ISBN 1848825102
  2. ^ a b Stefan Schlag, Bala Suresh, Masahiro Yoneyama (October 2007). "SRI Consulting CEH Report – Hydrogen". SRI Consulting. http://www.sriconsulting.com/CEH/Public/Reports/743.5000/. Retrieved 2010-07-01. 
  3. ^ "The National Hydrogen Association". Hydrogenassociation.org. 2004-08-13. http://www.hydrogenassociation.org/general/faqs.asp#howmuchproduced. Retrieved 2010-07-01. 
  4. ^ a b "Transport and the Hydrogen Economy". World-nuclear.org. http://www.world-nuclear.org/info/inf70.html. Retrieved 2010-07-01. 
  5. ^ The iea energy technology essentials are regularly updated briefs that draw together the best-available, consolidated information on energy technologies from the iea network, April 2007.
  6. ^ a b c d e f g h i j Tao, Yongzhen; Chen, Yang; Wu, Yongqiang; He, Yanling; Zhou, Zhihua (February 2007). "High hydrogen yield from a two-step process of dark- and photo-fermentation of sucrose". International Journal of Hydrogen Energy 32 (2): 200–206. doi:10.1016/j.ijhydene.2006.06.034. ISSN 0360-3199. http://www.sciencedirect.com/science/article/B6V3F-4KGPP8H-1/2/a2e03311e524ba2baeb47e720d9c47e5. 
  7. ^ Algae: Power Plant of the Future?
  8. ^ Reengineering Algae To Fuel The Hydrogen Economy
  9. ^ Algae Could One Day be Major Hydrogen Fuel Source Newswise, Retrieved on June 30, 2008.
  10. ^ Melis A and Happe T (2001). "Hydrogen Production. Green Algae as a Source of Energy". Plant Physiol. 127 (3): 740–748. doi:10.1104/pp.010498. PMC 1540156. PMID 11706159. http://www.plantphysiol.org/cgi/content/full/127/3/740. 
  11. ^ Growing hydrogen for the cars of tomorrow
  12. ^ 2004-Updated Cost Analysis of Photobiological Hydrogen
  13. ^ 2004- Updated cost analysis of photobiological hydrogen production from chlamydomonas reinhardtii green algae
  14. ^ Photobiological hydrogen production—prospects and challenges
  15. ^ 2005-A prospectus for biological H2 production
  16. ^ a b c Kapdan, Ilgi Karapınar; Kargı, Fikret (2006). "Biohydrogen production from waste materials". Enzyme and Microbial Technology. http://www.ichet.org/ihec2005/files/manuscripts/Kargi%20F.-Tr.pdf. 
  17. ^ a b c d e f Krupp, M.; Widmann, R (May 2009). "Biohydrogen production by dark fermentation: Experiences of continuous operation in large lab scale". International Journal of Hydrogen Energy 34 (10, Sp. Iss.SI): 4509–4516. doi:10.1016/j.ijhydene.2008.10.043. 
  18. ^ a b Verschuere, L; Rombaut,, G; Sorgeloos, P; Verstraete, W (December 2000). "Probiotic Bacteria as Biological Control Agents in Aquaculture". Microbiology and Molecular Biology Reviews 64 (4): 655–71. doi:10.1128/MMBR.64.4.655-671.2000. PMC 99008. PMID 11104813. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=99008. 
  19. ^ Watanabe, Hisanori; Yoshino, Hidekichi (May 2010). "Biohydrogen using leachate from an industrial waste landfill as inoculum". Renewable Energy 35 (5): 921–924. doi:10.1016/j.renene.2009.10.033. 
  20. ^ a b c Villadsen, John; Nielsen, Jens Høiriis; Lidén, Gunnar (2003). Bioreaction Engineering Principles (2 ed.). Springer. ISBN 9780306473494. http://books.google.com/?id=htUeM34b7KgC&lpg=PP1&dq=Bioreaction%20Engineering%20Principles&pg=PP1#v=onepage&q. 
  21. ^ Lee, Jae-Hwa; Lee, Dong-Geun; Park, Jae-Il; Kim, Ji-Youn (JAN 2010). "Biohydrogen production from a marine brown algae and its bacterial diversity". Korean Journal of Chemical Engineering 27 (1): 187–192. doi:10.1007/s11814-009-0300-x. 
  22. ^ Kahn, Amanda E.; Durako, Michael J. (October 2009). "Wavelength-specific photo-synthetic responses of Halophila johnsonii from marine-influenced versus river-influenced habitats". Aquatic Botany 91 (3): 245–249. doi:10.1016/j.aquabot.2009.06.004. 
  23. ^ a b THE NORTH STATE, www.thenorthstate.com. "Sunlight Direct". Sunlight Direct. http://www.sunlight-direct.com. Retrieved 2010-07-01. 
  24. ^ Nath, K; Kumar, A; Das, D (September 2005). "Hydrogen production by Rhodobacter sphaeroides strain OU001 using spent media of Enterobacter cloacae strain DM11". Applied Microbiology and Biotechnology 68 (4): 533–541. doi:10.1007/s00253-005-1887-4. PMID 15666144. 
  25. ^ a b Yang, Honghui; Guo,, Liejin; Liu, Fei (March 2010). "Enhanced bio-hydrogen production from corncob by a two-step process: Dark- and photo-fermentation". Bioresource Technology 101 (6): 2049–2052. doi:10.1016/j.biortech.2009.10.078. PMID 19963373. 
  26. ^ Redwood, M.D., Paterson-Beedle, M., Macaskie, L.E., 2009. Integrating dark and light biohydrogen production strategies: towards the hydrogen economy. Rev. Environ. Sci. Bio/Technol. 8:149-185.| url=http://www.springerlink.com/content/h77n7370t70643k7/
  27. ^ a b c d e f g h i j k l m n o Mathews, Juanita; Wang, Guangyi (September 2009). "Metabolic pathway engineering for enhanced biohydrogen production". International Journal of Hydrogen Energy 34 (17, Sp. Iss. SI): 7404–7416. doi:10.1016/j.ijhydene.2009.05.078. 
  28. ^ "KEGG PATHWAY: Pyruvate metabolism - Clostridium acetobutylicum". Genome.jp. http://www.genome.jp/kegg-bin/show_pathway?cac00620. Retrieved 2010-07-01. 
  29. ^ a b c d Koku, H; Eroglu, I; Gunduz, U; Yucel, M; Turker, L (2002). "Aspects of the metabolism of hydrogen production by Rhodobacter sphaeroides". International Journal of Hydrogen Energy 27 (11–12): 1315–1329. doi:10.1016/S0360-3199(02)00127-1. 

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