Biohydrogen
How Biohydrogen Is Produced
What Is Biohydrogen?
Hydrogen is the lightest known element and occurs naturally throughout the universe. It can be produced by a number of means including chemical reactions, or biologically by living organisms (usually bacteria). When this latter process takes place the resultant hydrogen is known as Biohydrogen.This is a hot topic at the moment because Biohydrogen has the potential to provide a non-polluting and sustainableenergy source. Industrial production of hydrogen today is mainly through processes which involve the burning of fossil fuels with a resultant toxic byproduct from the process, so there is great interest in Biohydrogen.
A Brief History of Biohydrogen
In 1939 a German scientist, Hans Gaffron,who had fled Europe during the rise of the Nazi Party in the 1930's and come to the University of Chcago noticed that a type of pond scum, found all over the world, called Chlamydomonas reinhardtii, would occasionally change from producing oxygen, like other plant forms, and for a short period produce hydrogen instead.
Scientists endeavoured to tap the potential energy source for the next 60 years without success. Then in 1999 there was a major advance when Professor Tasios Melis of the University of California at Berkeley and researchers from the National Renewable Energy Lab, discovered that depriving the algae of sulfur and oxygen would enable it to
produce hydrogen for prolonged periods of time. Scientists have now established that micro organisms produce biohydrogen by three different processes: Biophotolysis of water, Anoxygenic photosynthesis by photosynthetic bacteria, and Dark fermentation by anaerobic bacteria.
Production Of Biohydrogen
Biophotolysis of water
Photosynthesis is a process whereby light energy (usually natural sunlight) triggers, or is involved in, biochemical energy. Usually this results in the production of sugar phosphates. However under certain circumstances some microalgae and cyanobacteria produce hydrogen. The drawback with this method is the process is too prone to slipping back into producing oxygen to ensure sustainable hydrogen production and necessitates light to initiate the biochemical reaction.
Anoxygenic photosynthesis by photosynthetic bacteria
Oxygenic photosynthesis is the process by which algae, plants and most bacteria convert carbon dioxide to a carbohydrate. To effect the conversion light energy triggers a biochemical reaction that releases oxygen. However some types of bacteria can carry out Anoxygenic photosynthesis. In this method the light energy instigates a biochemical reaction that results not in oxygen but, amongst other things, hydrogen.
Dark fermentation by anaerobic bacteria
Biohydrogen can be produced through a process which does not require light and because of this it is known as dark fermentation. Aerobic means with oxygen, anaerobic means without oxygenwhile fermentation means the breaking down of a substance into its component parts. It follows therefore that anaerobic fermentation does not release oxygen. Some anaerobic bacteria release hydrogen and this makes possible the mass production of hydrogen from comparatively straight forward procedures, utilising a wide range of sources including refuse and waste products. Furthermore the production of hydrogen from this process usually goes on at a higher rate than in other processes. But, even though the rate of hydrogen production is faster than that attained by other methods the amount produced is normally less.
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