The biological hydrogen
production with algae
is a method of photobiological water splitting which is done in a closed
photobioreactor based on the production of hydrogen as a solar fuel
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.
Photosynthesis
Photosynthesis
in cyanobacteria
and green
algae splits water into hydrogen ions and electrons. The electrons are
transported over ferredoxins. Fe-Fe-hydrogenases (enzymes) combine them into hydrogen
gas. In Chlamydomonas reinhardtii Photosystem
II produces in direct conversion of sunlight 80% of the electrons that end
up in the hydrogen gas. Light-harvesting complex photosystem II light-harvesting
protein LHCBM9 promotes efficient light energy dissipation. The
Fe-Fe-hydrogenases need an anaerobic environment as they are inactivated by
oxygen. Fourier transform infrared spectroscopy
is used to examine metabolic pathways.
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.
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. He 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. Chlamydomonas moewusii
is also a good strain for the production of hydrogen.
Milestones
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.
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.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
2007 - Anastasios
Melis studying solar-to-chemical energy conversion efficiency in tlaX
mutants of Chlamydomonas reinhardtii, achieved 15% efficiency,
demonstrating that truncated Chl antenna size would minimize wasteful dissipation of
sunlight by individual cells 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%.
2009 - A team from the University
of Tennessee, Knoxville and Oak Ridge National Laboratory stated that the
process was more than 10 times more efficient as the temperature increased.
2011 - Adding a bioengineered
enzyme increases the rate of algal hydrogen production by about 400 percent.
2011 - A team at Argonne's
Photosynthesis Group demonstrated how platinum nanoparticles can be linked to
key proteins in algae to produce hydrogen fuel five times more efficiently.
Research
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.
As of 2009, HydroMicPro is testing
plate reactors.
As of 2013, Grow Energy has
developed novel system for the large-scale production of hydrogen from
structural bioreactors.
Areas of research to increase
efficiency include developing oxygen-tolerant FeFe-hydrogenases
and increased hydrogen production rates through improved electron transfer.
Economics
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.
In 2004, the US Department of Energy
issued a selling price of $2.60 per kilogram ($1.18/lb) 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 2004 achieved-efficiency is
only 1% and the 2004 actual selling price is estimated at $13.53 per kilogram
($6.14/lb)
According to a 2004 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.
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.
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