Biological hydrogen production is a method of photobiological water splitting which done in a closed photobioreactor based on the production of hydrogen by algae. Algae produce hydrogen under certain conditions. In 2000 it was discovered that if C. reinhardtii algae are deprived of sulfur they will switch from the production of oxygen, as in normal photosynthesis, to the production of hydrogen.[1][2]
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Bioreactor design issues
- Restriction of photosynthetic hydrogen production by accumulation of a proton gradient.
- Competitive inhibition of photosynthetic hydrogen production by carbon dioxide.
- Requirement for bicarbonate binding at photosystem II (PSII) for efficient photosynthetic activity.
- Competitive drainage of electrons by oxygen in algal hydrogen production.
- Economics must reach competitive price to other sources of energy and the economics are dependent on several parameters.
- A major technical obstacle is the efficiency in converting solar energy into chemical energy stored in molecular hydrogen.
Attempts are in progress to solve these problems via bioengineering.
Truncated antenna
The chlorophyll (Chl) antenna size in green algae is minimized, or truncated, to maximize photobiological solar conversion efficiency and H2 production. The truncated Chl antenna size minimizes absorption and wasteful dissipation of sunlight by individual cells, resulting in better light utilization efficiency and greater photosynthetic productivity by the green alga mass culture[3].
Milestones
1939 German researcher by the name of Hans Gaffron discovered while working at the University of Chicago, that algae can switch between producing oxygen and hydrogen.
1997 Professor Anastasios Melis discovered, after following Hans Gaffron's work, that the deprivation of sulfur will cause the algae to switch from producing oxygen to producing hydrogen. The enzyme, hydrogenase, he found was responsible for the reaction.[4][5]
2006 - Researchers from the University of Bielefeld and the University of Queensland have genetically changed the single-cell green alga Chlamydomonas reinhardtii in such a way that it produces an especially large amount of hydrogen.[6] The Stm6 can, in the long run, produce five times the volume made by the wild form of alga and up to 1.6-2.0 percent energy efficiency.
2007 - It was discovered that if copper is added to block oxygen generation algae will switch from the production of oxygen to hydrogen[7]
2007 - Anastasios Melis studying solar-to-chemical energy conversion efficiency in tlaX mutants of Chlamydomonas reinhardtii, achieved 15 % efficiency, demonstrating that truncated Chl antenna[8] size would minimize wasteful dissipation of sunlight by individual cells[9] This solar-to-chemical energy conversion process could be coupled to the production of a variety of bio-fuels including hydrogen.
2008 - Anastasios Melis studying solar-to-chemical energy conversion efficiency in tlaR mutants of Chlamydomonas reinhardtii, achieved 25 % efficiency out of a theoretical maximum of 30%[10].
Research
- 2006 - At the University of Karlsruhe, a prototype of a bio-reactor containing 500-1,000 litres of algae cultures is being developed. The reactor is to be used to prove the economic feasibility of the system in the next five years.
- 2009 - HydroMicPro is testing plate reactors[11]
Economics
It would take about 25,000 square kilometres to be sufficient to displace gasoline use in the US; this is less than a tenth of the area devoted to growing soya in the US dedicated to raising this form of algae.[12]
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.[13]
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[14].
Areas of research to increase efficiency include developing oxygen-tolerant FeFe-hydrogenases[15] and increased hydrogen production rates through improved electron transfer[16].
History
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.[17] 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.[18] 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.[19][20]
See also
References
- ^ Wired-Mutant Algae Is Hydrogen Factory
- ^ http://www.science.org.au/nova/newscientist/111ns_002.htm
- ^ 2004-Maximizing photosynthetic efficiencies and hydrogen production in microalgal cultures
- ^ Department of Energy report winter 2000
- ^ 2005-The anaerobic life of the photosynthetic alga
- ^ Hydrogen from algae - fuel of the future?
- ^ Copper
- ^ Chl antenna
- ^ DOE 2007 Report 15 %
- ^ DOE 2008 Report 25 %
- ^ Hydrogen from microalgae
- ^ Growing hydrogen for the cars of tomorrow
- ^ 2004-Updated Cost Analysis of Photobiological Hydrogen
- ^ 2004- Updated cost analysis of photobiological hydrogen production from chlamydomonas reinhardtii green algae
- ^ Photobiological hydrogen production—prospects and challenges
- ^ 2005-A prospectus for biological H2 production
- ^ Algae: Power Plant of the Future?
- ^ Reengineering Algae To Fuel The Hydrogen Economy
- ^ Algae Could One Day be Major Hydrogen Fuel Source Newswise, Retrieved on June 30, 2008.
- ^ Melis A and Happe T (2001). "Hydrogen Production: Green Algae as a Source of Energy". Plant Physiol. 127: 740–748. doi:. PMID 11706159. http://www.plantphysiol.org/cgi/content/full/127/3/740.
External links
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