Biohydrogen reactor

Biohydrogen reactors use a method of photobiological water splitting which is 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]

Contents

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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.[3] 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.[4] 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.[5][6]

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.[7][8]

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.[9] 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[10]

2007 - Anastasios Melis studying solar-to-chemical energy conversion efficiency in tlaX mutants of Chlamydomonas reinhardtii, achieved 15 % efficiency, demonstrating that truncated Chl antenna[11] size would minimize wasteful dissipation of sunlight by individual cells[12] 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%[13].

Research

As of 2009, HydroMicPro is testing plate reactors.[14]

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.[15]

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.[16]

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[17]. All those estimates however are obsolete in light of the previously mentioned improvements in efficiency, and the citations for the above estimates are dated 2004.

Areas of research to increase efficiency include developing oxygen-tolerant FeFe-hydrogenases[18] and increased hydrogen production rates through improved electron transfer[19].

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[20].

Bioreactor design issues

Attempts are in progress to solve these problems via bioengineering.

See also

References

External links