Biological hydrogen production
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Biohydrogen is H2 that is produced biologically. Interest is high in this technology because H2 is a clean fuel and can be readily produced from certain kinds of
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
. Many challenges characterize this technology, including those intrinsic to H2, such as storage and transportation of a noncondensible gas. Hydrogen producing organisms are poisoned by O2. Yields of H2 are often low.


Biochemical principles

The main reactions involve
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
of sugars. Important reactions start with glucose, which is converted to
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
: :C6H12O6 + 2 H2O -> 2 CH3COOH + 2 CO2 + 4 H2 A related reaction gives
formate Formate (IUPAC name: methanoate) is the conjugate base of formic acid. Formate is an anion () or its derivatives such as ester of formic acid. The salts and esters are generally colorless.Werner Reutemann and Heinz Kieczka "Formic Acid" in ''Ull ...
instead of carbon dioxide: :C6H12O6 + 2 H2O -> 2 CH3COOH + 2 HCOOH + 2 H2 These reactions are exergonic by 216 and 209 kcal/mol, respectively. H2 production is catalyzed by two hydrogenases. One is called eFehydrogenase; the other is called iFehydrogenase. Many organisms express these enzymes. Notable examples are members of the genera
Clostridium ''Clostridium'' is a genus of anaerobic, Gram-positive bacteria. Species of ''Clostridium'' inhabit soils and the intestinal tract of animals, including humans. This genus includes several significant human pathogens, including the causative ag ...
, Desulfovibrio, Ralstonia, and the pathogen '' Helicobacter''. ''
E. coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' is the workhorse for genetic engineering of hydrogenases. It has been estimated that 99% of all organisms utilize
dihydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, and ...
(H2). Most of these species are microbes and their ability to use H2 as a metabolite arises from the expression of H2 metalloenzymes known as hydrogenases. Hydrogenases are sub-classified into three different types based on the active site metal content: iron-iron hydrogenase, nickel-iron hydrogenase, and iron hydrogenase.


Production by algae

The biological hydrogen production with
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
is a method of photobiological water splitting which is done in a
closed Closed may refer to: Mathematics * Closure (mathematics), a set, along with operations, for which applying those operations on members always results in a member of the set * Closed set, a set which contains all its limit points * Closed interval, ...
photobioreactor image:Bioreaktor quer2.jpg, Moss bioreactor, Moss photobioreactor to cultivate mosses like ''Physcomitrella patens'' at the laboratory scale A photobioreactor (PBR) refers to any cultivation system designed for growing Photoautotrophism, photoautotr ...
based on the
production of hydrogen Hydrogen production is the family of industrial methods for generating hydrogen gas. As of 2020, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming of natural gas and other light hydrocarbons, partial oxidation of h ...
as a
solar fuel A solar fuel is a synthetic chemical fuel produced from solar energy. Solar fuels can be produced through photochemical (i.e. activation of certain chemical reactions by photons), photobiological (i.e., artificial photosynthesis), thermochemical ( ...
by
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
.
Algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
produce hydrogen under certain conditions. In 2000 it was discovered that if '' C. reinhardtii'' algae are deprived of
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
they will switch from the production of oxygen, as in normal photosynthesis, to the production of hydrogen.


Photosynthesis

Photosynthesis in
cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
and
green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...
splits water into hydrogen ions and electrons. The electrons are transported over
ferredoxin Ferredoxins (from Latin ''ferrum'': iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied t ...
s. Fe-Fe-hydrogenases (enzymes) combine them into hydrogen gas. In ''Chlamydomonas reinhardtii''
Photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem ...
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 Fourier-transform infrared spectroscopy (FTIR) is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectr ...
is used to examine metabolic pathways. In 2020 scientists reported the development of algal-cell based micro-droplets for multicellular spheroid microbial reactors capable of producing hydrogen alongside either oxygen or CO2 via photosynthesis in daylight under air. Enclosing the microreactors with synergistic bacteria was shown to increase levels of hydrogen production. Available unde
CC BY 4.0


Specialized chlorophyll

The
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...
(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.


Economics

It would take about 25,000 square kilometre algal farming to produce biohydrogen equivalent to the energy provided by gasoline in the US alone. This area represents approximately 10% of the area devoted to growing soya in the US.


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 Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem ...
(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 Biological engineering or bioengineering is the application of principles of biology and the tools of engineering to create usable, tangible, economically-viable products. Biological engineering employs knowledge and expertise from a number o ...
.


History

In 1933, Marjory Stephenson and her student Stickland reported that cell suspensions catalysed the reduction of
methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglobin ...
with H2. Six years later,
Hans Gaffron Dr. Hans Gaffron was born in Lima, Peru, on May 17, 1902, and was a son of the German physician Eduard Gaffron and his wife Hedwig von Gevekot. He was one of the earlier researchers trying to elucidate the mechanistic and biochemical details of ...
observed that the green photosynthetic alga '' Chlamydomonas reinhardtii'', would sometimes produce hydrogen. In the late 1990s
Anastasios Melis Anastasios Melis is an American biologist at the University of California, Berkeley who elucidated the possibility of creating hydrogen from algae. He is currently Professor of Plant & Microbial Biology in the institution and Editor-in-Chief of the ...
discovered that deprivation of sulfur induces the alga to 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 also discovered that depleting the amount of sulfur available to the algae interrupted their internal oxygen flow, allowing the hydrogenase an environment in which it can react, causing the algae to produce hydrogen. ''Chlamydomonas moewusii'' is also a promising strain for the production of hydrogen.


Industrial hydrogen

Competing for biohydrogen, at least for commercial applications, are many mature industrial processes. Steam reforming of natural gas - sometimes referred to as steam methane reforming (SMR) - is the most common method of producing bulk hydrogen at about 95% of the world production. :CH4 + H2O <-> CO + 3 H2


See also

* Algaculture * Hydrogen production * Hydrogenase * Photohydrogen * Timeline of hydrogen technologies


References


External links


DOE - A Prospectus for Biological Production of HydrogenMaximizing Light Utilization Efficiency and Hydrogen Production in Microalgal CulturesDIY Algae/Hydrogen Bioreactor 2004EERE-CYCLIC PHOTOBIOLOGICAL ALGAL H2-PRODUCTION
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