A microscopic mutant algae that was discovered 60 years ago, has a better use of sunlight than their cousins. They can split water into hydrogen and oxygen up to three times more than other species of algae. Thus this species of algae is very promising for production of hydrogen which can be used in fuel cell, and moreover it saves the electricity which was used to electrolyze water molecule to generate hydrogen and oxygen and higher algae planting promises good production of oil for bio fuels.
Those algae have low chlorophylls in their cells and so absorbing low sunlight, thus higher yield of algae per unit area and hence more algae in sunlight making more hydrogen.
Current work in this field is trying to minimize amount of chlorophylls in algae, naturally occurring algae has 600 molecules of chlorophylls in its chloroplast but now scientist trying to reduce it down to 130, they succeeded to make it 300 at present and hence to improve the efficiency of these power plants.
Keywords: Mutant algae, Hydrogen, Fuel Cells, Chlorophyll
Introduction:
Hydrogen, the most productive and useful element of the periodic table is the possible future carrier of energy on an economy-wide scale. Its use has now expanded to the field of automotive, chemical, power generation, aerospace, and telecommunications industries. Unfortunately, Hydrogen gas (H2) is not readily found in nature, and if generated by fossil fuels or nuclear power, it falls outside the renewable energy sphere. Its Industrial preparation can be done by Steam reforming of Natural Gas, or by Haber's Process. In Laboratory, it can be prepared by the reaction of acids on metals or even by electrolysis of water, which requires electricity generated from fossil fuels or from renewable sources such as wind or solar energy. Hydrogen production under anaerobic conditions can be described by Schikorr's reaction as shown in (1):
Fe + 2 H2O → Fe (OH)2 + H2
3 Fe (OH)2 → Fe3O4 + 2 H2O + H2
Ferrous hydroxide → magnetite + water + hydrogen (1)
There are thermo-chemical cycles as well for the production of Hydrogen without the use of electricity. But, being expensive, these methods are only a temporary fix.
Few mutant algae's like Chlamydomonas Reinhardtii, Rhodospirillum rubrum, Rubrivivax gelatinosus CBS, Scenedesmus obliquus, Anabena, Rhodobacter Sphaeroides RV produce bio-hydrogen under certain suitable conditions. Alga is the cleanest and cost-efficient biological hydrogen producing source.
History:
Hydrogen from renewable and sustainable sources, without environmental degradation was required. Many tremendous strides have been taken in this field so far. Finding an efficient and renewable method by which the H2 producing organism can be supplied energy has become a priority.
One such effort was undertaken by a collaboration of scientists from the University of California-Berkley, the National Renewable Energy Laboratory, and the Botanisches Institut der Universität Bonn. Those scientists were influenced by the peculiar properties of algae, to discover an excellent source of renewable H2. By imposing Sulphur deprivation upon algae cells of Chlamydomonas reinhardtii (a green-algae) in a starchy growth medium, a chain reaction of events allow the production of H2. The purpose of this paper is to analyze this technical advance in renewable H2 production from an environmental and ecological perspective. Along those lines, this paper takes an in-depth look at the biological, physiological, and chemical components of this discovery.
Sustainable Energy Sources in Use Today:
Sustainable energy sources are now recognised as the more efficient way to produce energy. There have been great advances in this field. For example, solar, wind, water, and biomass based energy can truly be harnessed to provide heat and electricity, but many strides still have to be made before they can sustain the global energy demand.
The disadvantages of solar power are low efficiency, high cost, and need for steady access to sun. Wind power is challenging because steady winds are required. Land use is intensive, and visual and noise pollution are created. There is a possibility of ecosystem interference by altering migratory bird patterns as well. Likewise, water power presents obstacles such as construction costs, CO2 emissions from decaying biomass in shallow tropical reservoirs, floods, and ecosystem conversions, danger of collapse, harms fish and mineralization.[1] Finally, biomass burning has disadvantages including renewability, CO2 emissions, low efficiency, soil erosion, and water and air pollution .
Fortunately, a new source of sustainable energy is being developed which will revolutionize sustainable energy production, which is based on the peculiar properties of Green Algae, C. Reinhardtii found in common pond scum.[2] It uses the peculiar properties of Green Algae found in common pond scum to create H2.
Chlamydomonas Reinhardtii(a green-algae):
Chlamydomonas reinhardtii is the most widely used laboratory species of algae. This is because it grows rapidly, while being easy and inexpensive to culture, and it is amenable to standard genetic analysis.[3] The biochemistry and physiology of Chlorophyta, Chlamydomonas reinhardtii has been intriguing scientists for years because of some of its more peculiar properties, although its basic biological functions have been well known for years.
C. Reinhardtii has a cell wall (which is a clear to semi-clear gelatinous like layer 5-10 microns in diameter), a chloroplast (essential for photon absorption and electron generation), a light perceiving mechanism (to find the sun's light), a mitochondria (for cellular respiration), a starch granule (for energy storage) and two anterior flagella each 10 microns long (for manoeuvring in liquid).[4] Generally, Algae requires:
(1) Carbon- obtained from carbon dioxide or hydrocarbonate (HCO3-)
(2) Nitrogen- obtained from nitrate ion (NO3-)
(3) Phosphorus- as some form of orthophosphate
(4) Sulphur- obtained from sulphate (SO4-)
(5) Trace elements including sodium, potassium, calcium, magnesium, iron, cobalt, and molybdenum.[5]
4.1. Functioning:
Under anaerobic conditions, C. Reinhardtii, in the absence of sulphur produces hydrogen, instead of oxygen, normally produced by the oxygenic photosynthesis. Depleting the amount of sulphur available interrupts the internal oxygen flow of this green-alga.
Hydrogenase, an enzyme active only in the absence of oxygen generates hydrogen by splitting water by the process of photo-production of Hydrogen as shown in (2).
2H2O ïƒ 4H+ + 4e− + O2 (2)
The photophosphorylation (production of ATP using energy of sunlight) of Water molecule gives Hydrogenase enzyme, [Fe]-HydA in the Chloroplast, represented in (3).
PHOTOPHOSPHORYLATION
H2O--------------------------->[Fe]-HydA (3)
In photophosphorylation, light energy is used to create a high energy electron donor and a lower energy electron acceptor. Electrons then move simultaneously from donor to acceptor through an electron transport chain.[2] [Fe]-HydA contains unique 2Fe2S (Iron and Sulphur) metallo-cluster in the catalytic center in the core of proteins.
The protons and electrons extracted from water can be fed to the Hydrogenase enzyme ([Fe]-HydA) via electron transport chain to drive the direct photo-production of Bio-Hydrogen, as shown in (4).
4H+ + [Fe]-HydA ïƒ 2H2 (4)
In the mitochondrion, Nicotinamide adenine dinucleotide ion (NAD+) is formed from the Starch present. With the help of electron transport activity, NAD+ is reduced to NADH, which can be used as a reducing agent to donate electrons. The oxidative phosphorylation of NADH gives O2 which is further converted into H20 by biological processes, as represented by (5).
OXIDATIVE PHOSPHORYLATION
NADH ---------------------------------> O2 (5)
The release of H2 gas serves to sustain baseline levels of chloroplast and mitochondrial electron transport activity for the generation of ATP, which is needed for the survival of the organism under the protracted sulphur deprivation stress conditions.[2]
Under the prevailing anaerobic conditions, oxidative phosphorylation in mitochondria of the green algae would also be inhibited, thus depriving the cells of another source of ATP. However, expression of the [Fe]-hydrogenase and the release of gaseous H2 permit a slow rate of electron transport in the thylakoid membrane of photosynthesis, which is coupled to electron transport in mitochondria, lea-ding to ATP generation in both organelles.
Interplay between oxygenic photosynthesis, mitochondrial respiration, catabolism of endogenous substrate, and electron transport via the hydrogenase pathway is essential for the light-mediated H2 production process.
Efficiency:
Algae transform visible light in the range of 400-700 nm of the spectrum (Photosynthetically active radiation) into chemical energy which is further converted to Hydrogen by the catalyst, Hydrogenase. The process of Hydrogenase catalysed H2 production is short lived due to its inactivation by the photosynthetically generated O2. The sunlight to hydrogen conversion efficiency (STH) in green algae is estimated to be about 12.5% which is high in comparison to its Nitrogenase catalysed formation. This is mainly because the former process does not require the accumulation of an organic waste. STH conversion efficiency can be calculated as follows:
STH Conversion Efficiency = (i . iv) /(ii . iii)
Where i is the fraction of incident sunlight absorbed by photosynth-etic organisms (green algae and cyanobacteria) = around 45%; ii is the number of absorbed photons required to produce 1 mole of H2 = 4 Photons; iii is the energy content of an average visible light photon (550nm) = 52 kcal/photon; and iv is the energy content of a mole of H2 = 64 kcal.
However, due to a number of physiological reasons, this value has not been achieved yet but it sets the maximum potential efficie-ncy to be expected from living systems.
The films of micro-algae comprising of 5 to 20 cellular mon-olayers were entrapped on a filter paper, thereby constraining them in a well-defined circular geometry. Using Tin-oxide Semiconductor gas sensor, the conversion efficiency of visible polychromatic light into Hy-drogen has been found to be ab-out 6%.
Effect of Light on amount of Hydrogen produced and Cell Growth:
'OD' measures the light scattering, which varies inversely with the wavelength. Since green colour absorbs shorter wavelength, so to obviate the error due to absorbance, we take 550nm in cytoplasmic lipid bodies (LBs).
LB production in C. Reinhardtii is unique in itself. The efficiency of Hydrogen production and cell growth is measured by the rate of H2 production and OD660nm respectively.
'Insert TABLE 1'
The statistics in TABLE 1 show that, OD550nm (cell growth) is highest for Succinate per 20 mmol/litre concentration. It also shows that the highest RHP is given using Acetate as the sole electron donor.
The GRAPH 1 shows that the optimal light intensity for AHP is between 6000 ~ 9000 lx. The result indicates that photo-production of molecular Hydrogen by C. Reinhar-dtii is regulated by light intensity.[6]
'Insert GRAPH 1'
Effect of Metal Ions Concentration on Hydrogen Production and Cell Growth:
By testing the influence of interaction among metal ions (Ni2+ and Fe3+), Acetate and Glutamate in aqueous solution, following results were obtained for H2 production and Cell growth of C. Reinhardtii as shown in TABLE 2.
'Insert TABLE 2'
The TABLE 2 illustrates that Ni2+ inhibits H2 evolution, but accelerates cell growth. The influence of glutamate concentration on cell growth is higher than that of both acetate and Ni2+ concentrations. In contrast to Ni2+, Fe3+ is a key to H2 production and the effect of acetate concentration on H2 production is higher than that of glutamate concentration.[7]
Use of produced Hydrogen in Fuel Cells:
In a typical fuel cell, Hydrogen is fed continuously to the anode (negative electrode) compartment and an oxidant (i.e., oxygen from air) is fed continuously to the cathode (positive electrode) compartment; the electrochemical reactions take place at the electrodes to produce an electric current. The fuel cell is an energy conversion device that has the capability of producing electrical energy for as long as the fuel and oxidant are supplied to the electrodes. It consists of an electrolyte sandwiched between two electrodes, an anode and a cathode. Bipolar plates on either side of the cell help distribute gases and serve as current collectors. In a Polymer Electrolyte Membrane (PEM) fuel cell, which is widely regarded as promising for light-duty transportation, hydrogen gas flows through channels to the anode, where a catalyst causes the hydrogen molecules to separate into protons and electrons. The membrane allows only the protons to pass through it. While the protons are conducted through the membrane to the other side of the cell, the stream of negatively-charged electrons follows an external circuit to the cathode. This flow of electrons is electricity, that can be used to power a motor or for other electricity generation purposes.
Sir William Grove first demonstrated the conversion of hydrogen to electricity using an acid-electrolyte fuel cell in 1839. However, turning this idea into a practical means of energy conversion has proved to be elusive.
Hydrogen produced from Algae's will assist in the supply of electrons to the Fuel cells resulting in an eco-friendly power generation.
Conclusion:
Although the currently obtained efficiency of AHP from C. Reinhardtii is not sufficient, the technology will improve in the coming years. At that time, it will prove to be a viable alternative to current energy sources. The authors believe that the catalytic principle of Hydrogenases, reduction in the oxygen sensitivity of enzyme and increase in the photosynthetic efficiency must be studied further which will help to develop vitro systems for efficient production of H2.
Inevitably, as all the other Hydrogen producing sources will get depleted, Algal-hydrogen production will surpass the cost of then-available energy source. This form of Hydrogen fuel production will efficiently replace traditional fuel for cars and heat for homes. It has the potential to create jobs and fuel the economies of countries that produce this form of energy. It might also lead to the decline in problems due to Greenhouse effect and may prove to be a groundbreaking discovery as Edison's electricity discoveries were.
Table of Authorities:
[1] Miller, Jr,, G. Tyler (2004) Living in the Environment, Canada: Thomson Learning Inc. Stanley E. Manahan, Environmental Chemistry, Lewis Pub. 6th Ed. 1994; 141.
[2] Melis A., Happe T. (2001) Hydrogen Production-Green Algae as a Source of Energy, Plant Physiology 127(3): 740-748.
[3] Shimogawara K., Fujiwara S., Grossman A., Usuda H. (1998) High-Efficiency Transformation of Chlamydomonas reinhardtii by Electroporation. Genetics 148: 1821-1828.
[4] Harris, E. H. (1989),The Chlamydomonas Sourcebook. Academic Press, New York. Prentice Hall, New Jersey
[5] Macnaghten P. and Jacobs M. 1997. Public Identification with Sustainable Development: Investigating Cultural Barriers To Participation, Global Environmental Change, 7: 1-20.
[6] K. Sasaki, Biohydrogen, Plenum Press, London, 1998, 133.
[7] Su Ping YANG, Zheng Wu WANG, Chun Gui ZHAO, Yin Bo QU, Xin Min QIAN, (2002) Generation of hydrogen from photolysis of organic acids by photosynthetic bacteria, Chinese Chemical Letters Vol. 13, No. 11, pp 1111 - 1114.
[8] "Fuel Cell Basics: Benefits". Fuel Cells(2000). Retrieved 2007-05-27. (http://www.fuelcells.org/basics/benefits.html)
[9] Vielstich, W., et al. (eds.) (2009). Handbook of fuel cells: advances in electrocatalysis, materials, diagnostics and durability. 6 vol. Hoboken: Wiley, 2009.
Tables:
Hydrogen Donor
[/20mmol L-1]
Rate of hydrogen production (RHP)
[ ml-1 L-1 h-1 ]
Cell growth
[OD550nm]
Formate
5.5
0.963
Acetate
15.3
1.213
Propionate
5.0
0.686
Butyrate
12.0
0.872
Pyruvate
3.0
1.182
Lactate
4.5
1.280
Malate
4.0
1.238
Citrate
2.0
0.859
Succinate
5.0
1.293
Gluconate
10.0
0.580
TABLE 1: The experimental results of RHP and cell growth for different organic acids (photo-decomposition) by C.Reinhardtii
Acetate (mmolL-1)
20
20
20
30
30
30
40
40
40
Glutamate (mmolL-1)
5
7
9
5
7
9
5
7
9
FeCl3.6H2O (µmolL-1)
50
90
120
90
120
50
120
50
90
NiCl2.6H2O (µmolL-1)
3
5
7
5
7
3
7
3
5
OD550nm
*
*
1.026
*
*
1.573
1.086
1.116
1.213
AHP (ml)
0
0
20
0
0
0
24
24
0
* : Cell Aggregation under these conditions
TABLE 2: Effects of the interaction among Ni2+, Fe3+ acetate and glutamate on AHP and cell growth
GRAPHS:
GRAPH 1: Effect of Light Intensity on Amount of Hydrogen Produced (AHP) with Acetate as Hydrogen Donor
