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Biohydrogen is defined as hydrogen produced biologically, most commonly by algae, bacteria and archaea. Biohydrogen is a potential biofuel
obtainable
from both cultivation and from waste organic materials.
Introduction
Currently, there is a huge demand for hydrogen.
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
.
An important future application of hydrogen
could be as an alternative for fossil fuels, once the oil deposits are
depleted. This application is however dependent on the development of storage
techniques to enable proper storage, distribution and combustion of hydrogen. If the cost of hydrogen production,
distribution, and end-user technologies decreases, hydrogen as a fuel could be
entering the market in 2020.
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.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.
Algal biohydrogen
In 1939 a German researcher named Hans
Gaffron, while working at the University of Chicago, observed that the alga he
was studying, Chlamydomonas
reinhardtii (a green alga), would sometimes switch from the production of
oxygen to the production of hydrogen. 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 algal 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. 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.
Bacterial biohydrogen
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.
The organic acids can be derived from any organic
material source such as sewage waste waters or agricultural wastes. 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.
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.
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