Biological hydrogen production (algae)
Biological hydrogen production is done in a bioreactor based on the production of hydrogen by algae. Algae produces hydrogens under certain conditions. In the late 1990's it was discovered that if you deprive the algae of sulfur it will switch from the production of oxygen, i.e. normal photosynthesis, to the production of hydrogen.
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.
- Economic feasibility-The energy efficiency - the conversion of sunlight into hydrogen - has to reach 7-10 percent (alga in its natural form achieves at most a meagre 0.1 percent).
Attempts are in progress to solve these problems via bioengineering.
Milestones
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.[[1]] 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.
2006 - Unpublished work from the University of California at Berkeley-(The program is done by Midwest Research Institute, the operating contractor for NREL)- may have brought the technology past the economically viable 10 percent efficiency level. By shortening the chlorophyll stacks in the photosynthetic organelles, Tasios Melis has "probably" passed the threshold.[[2]]
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.
Economics
An algae-farm the size of the state Texas would produce enough hydrogen to supply the needs of the whole world. About 25,000 square kilometres is enough to displace gasoline use in the US. (less than a tenth of what the US devotes to growing soya) [[3]].
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.[4] 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. [5] Chlamydomonas moeweesi is also a good strain for the production of hydrogen.