Biological_Hydrogen_Production

1. BIOLOGICAL HYDROGEN PRODUCTION

2. What is a hydrogen?
Hydrogen is a chemical element with
symbol H and atomic number 1. With an
atomic weight of 1.00794 u hydrogen is the
lightest element and its monatomic form
(H1) is the most abundant chemical
substance, constituting roughly 75% of the
Universe's baryonic mass. At standard
temperature and pressure, hydrogen is a
colorless, odorless , tasteless, non-toxic, non
metallic, highly combustible diatomic gas
with the molecular formula H2.

3. ABSTRACT
Biological hydrogen production presents a possible avenue
for the large scale sustainable generation of hydrogen needed to
fuel a future hydrogen economy. Moreover, low yields of
production also lead to the generation of side products whose
large scale production would generate a waste disposal problem.
Here recent attempts to overcome these barriers are reviewed and
recent progress in efforts to increase hydrogen yields through
physiological manipulation, metabolic engineering and the use of
two-stage systems are described.

4. INTRODUCTION
The world is turning to a search for clean energy
sources to mitigate coming climate change and the
impending shortage of readily available fuel to provide
the energy necessary for present and projected human
activities. A variety of possible fuel sources are being
examined at present. Among this, many have proposed
using hydrogen as an energy carrier in a future
hydrogen economy. However, a sustainable, renewable
supply of hydrogen to power this economy is required.

5. METHODS OF BIOLOGICAL
HYDROGEN PRODUCTION
 Light-driven bio hydrogen production
 Dark fermentative bio hydrogen production

6. LIGHT-DRIVEN BIO
HYDROGEN PRODUCTION
The usage of biological systems to react with solar energy and
convert it to energy in the form of hydrogen is Light-driven
bio hydrogen production. The two different types of Light-
driven bio hydrogen production are
#} biophotolysis using plant-type photosynthesis
#} photofermentation using bacterial photosynthesis

7. BIOPHOTOLYSIS
HYDROGEN PRODUCTION
 The power of photosynthesis to capture sunlight and split
water, a process that is called biophotolysis
 The natural capacity of microbial photosynthesis, either
microalgal or cyanobacterial, is used to capture solar energy
and split water.
 Highly reducing electrons produced by photosystem it can
be used to reduce a ferredoxin that can drive hydrogen
evolution by a hydrogenase enzyme.
 In this method clean water is not required, in fact some types
of wastewater would be preferred.
 Hydrogen production rate is 2.5–13%

8. GENERAL STRATEGIES FOR
IMPROVEMENT OF
PHOTOSYNTHETIC EFFICIENCIES
 Photosynthetic efficiency is the quantum requirement for
improvement of hydrogen production.
 The two main present targets for improvement hydrogen
production are
$ increasing the total spectrum that is captured,
$ increasing the quantity of light that is captured and
productively used at high light intensities.

9. STRATEGIES FOR INCREASED
HYDROGEN PRODUCTION IN
THE PRESENCE OF OXYGEN
The hydrogen present in green algae, like all other
known as hydrogenases, it is extremely sensitive to
oxygen, undergoing irreversible inactivation in the present
of even small amounts of oxygen. Creating an oxygen
tolerant hydrogenase would go a long way to making
biophotolysis a practical method of hydrogen production.

10. ADVANTAGES:-
 Abundant, inexhaustible substrate (water).
 Totally carbon independent pathway.
 Simple products, hydrogen and oxygen.
DISADVANTAGES:-
 Evolves oxygen, destroying the hydrogen evolving
catalyst.
 Low photosynthetic conversion efficiencies.
 Potentially explosive gas mixtures formed.
 Large surface areas required.
FUTURE PROSPECTS:-
 Near term incremental improvements possible through
creation of antenna mutants.
 Immobilization might bring some improvement.

11. BACTERIAL PHOTOSYNTHESIS
PHOTOFERMENTATION
 In biological hydrogen production due to their ability to capture
solar energy and carry out the conversion of substrates to
hydrogen for which this would not be possible without an
additional energy inputs.
 In addition, they are being investigated as part of two-stage
systems for deriving additional hydrogen from the effluents of
dark, hydrogen producing bioreactors.
 In the above case, hydrogen evolution is catalyzed by the ATP-
requiring nitrogenase enzyme, capable of reducing protons to
hydrogen in the absence of other substrates is known as
PHOTOFERMENTATION

12. STRATEGIES FOR IMPROVING
PHOTOFERMENTATION
A reduced pigment mutant of Rhodobacter sphaeroides was
reported to give higher hydrogen production, but only at low
(10 W/m2) light intensities.
 The difference at a higher light intensity (100 W/m2) was
quite small, difficult to explain since mutants with less
antenna pigment would be expected to greatly outperform
the wild-type under these conditions.
In principle, of this suppressing metabolic reactions that
divert electron flow away from nitrogenase should increase
hydrogen yields in photofermentation.

13. ADVANATGES:-
 Uses readily available waste streams.
 Nearly complete substrate conversion.
DIS ADVANATGES:-
 Low volumetric rates of production.
 Low efficiency hydrogen production by nitrogenase.
FUTURE PROSPECTS:-
 Strain improvement through metabolic engineering
replacement of N2 with H2.
 Near term improvement possible through creation of antenna
mutants.

14. DARK FERMENTATIVE
BIOHYDROGEN PRODUCTION
 The limitations of the natural metabolic process available for
hydrogen production in fermentation is shown in bellowed figure.
 Even though there is some diversity in pathways and various
hydrogen evolving hydrogenases is available.
 The major problem with existing pathways is that only one-third of
the substrate can be used for hydrogen production, with the remaining
twothirds (acetyl-CoA) forming another fermentation product as
acetate, butyrate, butanol, acetone, etc.
 In terms of the growth and survival of the organism this makes sense
because formation of some other products as e.g. acetate, allows ATP
formation while formation of other, reduced products allows the
oxidation of NADH, necessary to maintain redox balance in the
fermentation.

15. HYDROGEN PRODUCING FERMENTATION
PATHWAYS

16.  As in many other fermentations, glucose is broken down to pyruvate, generating ATP
and NADH.
 Pyruvate is then converted to acetyl-CoA, and depending upon the organism, either
formate, through the PFL pathway, or reduced ferredoxin and CO2, through the
PFOR pathway.
 Formate can be converted to hydrogen and CO2, by either the formate hydrogen
lyase pathway which contains a [NiFe], or possibly in some other organisms another
pathway which contains a formate dependent [FeFe] hydrogenase.
 NADH, generated during glycolysis, is oxidized through the production of various
reduced carbon compounds, typically ethanol.
 A variety of [FeFe] hydrogenases can be used to reoxidize ferredoxin and produce
hydrogen, including; a ferredoxin-dependent H2ase (Fd-[FeFe]).
 In some cases, NADH can also be used in hydrogen production, either by reducing
ferredoxin (NFOR), by directly reducing H2ase (NADH-[FeFe]), or as a co-substrate
with reduced ferredoxin (Fd-NADH-[FeFe]).
 Excess NADH is used to produce other reduced fermentation products. In both cases,
acetyl-CoA can also be used to produce ATP.

17. ADVANTAGES;-
 Can use a variety of waste streams.
 Simple reactor technology, nonsterile conditions
acceptable.
DISADVANTAGES:-
 Large amount of byproducts are required.
 Reactor to reactor variation.
 Low COD removal.
FUTURE PROSPECTS:-
 Two stage systems can extract additional energy,
decrease COD.

18. CONCLUSION
A variety of microbial paths to renewable
hydrogen production are available and are under active
study. Although a number of advances have been made
recently, there are a number of technical challenges in
each area that must be overcome before these
technologies can be adopted on a practical large scale.
Extensive R&D in this area is underway worldwide,
but practical development of biohydrogen production
is a long term prospect, commensurate with the time
frame required to adopt hydrogen as a major fuel
source.

19. REFERENCES
 Abo-Hashesh, M., Wang, R., Hallenbeck, P.C., 2011a. Metabolic
engineering in dark fermentative hydrogen production; theory
and practice. Bioresour. Technol. 102 (18), 8414–8422.
 Abo-Hashesh, M., Ghosh, D., Tourigny, A., Taous, A.,
Hallenbeck, P.C., 2011b. Single stage photofermentative
hydrogen production from glucose: An attractive alternative to
two stage photofermentation or co-culture approaches. Int. J.
Hydrogen Energy 36 (21), 13889–13895.
 Adessi, A., De Philippis, R., 2012. Hydrogen Production:
Photofermentation. In: Hallenbeck, P.C. (Ed.), Microbial
Technologies In Advanced Biofuels Production. Springer, New
York, pp. 53–75.
 Adessi, A., De Philippis, R., Hallenbeck, P.C., 2012. Combined
systems for maximum substrate conversion. In: Hallenbeck, P.C.
(Ed.), Microbial Technologies In Advanced Biofuels Production.
Springer, New York, pp. 107–126.
 Beer, L.L., Boyd, E.S., Peters, J.W., Posewitz, M.C., 2009.
Engineering algae for biohydrogen and biofuel production. Curr.
Opin. Biotech. 20, 264–271.

20. THANK YOU