The document related to the dark fermentation process, widely used for hydrogen production by using bacterial strains

1. Virendra Kumar

2. It can be produced from renewable feed stocks using
non-fossil energy sources
 Water is the only byproduct and does not produce any
green house gas
 Electricity can be produced directly via fuel cells
Good automotive fuel
Since fossil fuels contribute massive carbon emission
so we need to explore sustainable energy sources like
hydrogen and methane

3. Fuel type Energy/unit
mass, MJ/Kg
Energy /Vol
MJ/l
Carbon
emission
Kg C/Kg fuel
Hydrogen gas 120 2 0
Hydrogen liquid 120 8.5 0
Coal(anthracite) 15-19 - 0.5
Natural gas 33-50 9 0.46
Diesel 42.8 35 0.9
Biodiesel 37 33 0.5
Ethanol 21 23 0.5
Bossel et al. 2003

4. Hydrogen Production Processes
Physico chemical Process
Steam reforming of light HCs
Partial oxidation/Gasification
of heavier HCs/Coal
Thermal Cracking of Natural gas
Electrolysis of water
Biological Process
Bio photolysis
of water
(Direct/Indirect)
Photo fermentation
Dark fermentation
Integration of dark
fermentation with
photo fermentation
Most of the hydrogen is produced from hydrocarbon about 95%,
followed by electrolysis of water 4%, and only 1% is produced from
biomass through biological processes

5. Metabolic
Process
Organism Advantages Hydrogen
yield
(mmolH2/l.h)
Product
Direct
biophotolysis
Green algae Can produce H2
directly from water
0.07 H2, O2
Indirect
biophotolysis
Cyanobacteria Can produce H2
directly from water
0.36 H2, O2
Photofermentati
on
Phototrophic
bacteria
A wide variety of
spectral light
energy can be
used by bacteria
0.16 H2,CO2
Dark
fermentation
Fermentative
bacteria
A wide variety of
carbon source can
be used as
substrate
65-75 H2,CO2,
VFA
Biological Processes of Hydrogen Production
Source :Krupp, M. and Widmann, R. (2009) Biohydrogen production by dark fermentation: Experiences
of continuous operation in large lab scale, International journal of hydrogen energy, 34, pp.4509-16

6. Dark Fermentation is the fermentative conversion of
organic substrate to hydrogen
It is a complex process manifested by diverse group of
bacteria involving series of biochemical reactions, similar
to anaerobic conversion
In this, fermentative hydrolytic microorganisms
hydrolyze complex organic polymers to monomers,
which are further converted to a mixture of lower
molecular weight organic acids and alcohol by
acidogenic bacteria

7. Source :Sanjukta Subudhi, TERI, New Delhi, India , 3rd International Symposium on Biofuels and Bio-energy 19-20 April,
2012

8. Hydrogen producing Bacteria – These includes class
Clostridia - e.g. C. thermocellum, C. acetobutylicum
Bacilli- e.g. B. thuringiensis, Enterobacter faecium
Bacteriode- e.g. Bacteriodes capillosus
Mollicutes- e.g. Acholeplasma laidlawi
Gammaproteobacteria - e.g. Escherichia coli
Actinobacteria - e.g. Slackla heliotrinireducens
Methane producing Bacteria- These mostly belong to
class Archaea such as
Methanosorcina barkeri, Methanosorcina activorans are some
methanotrophs and Methanoculleus marinsnigri ,
Methanoregula boonei are some hydrogenotrophs

9. Microbes involved in different stages of hydrogen and
methane production
Source :Wirth, R., K, Etelka., M, Gergely., B, Zoltán. , R, Gábor., and Kornél L Kovács. (2012) Characterization of a biogas-
producing microbial community by short-read next generation DNA Sequencing, Biotechnology for Biofuels, 5,p.41

10. Industrial Waste Agricultural waste Others
Dairy industry Corn straw Synthetic waste
water
Distillery
effluent
Wheat straw Sewage waste
water and sludge
Food processing
waste water
Rice bran Food Waste
Sugar industry
(Press mud
Bagasse &
molasses )
Grass silage Kitchen waste
Substrates used in Dark fermentation

11. (a)
(c)
(b)
(d)
Figure : (a) CSTR, (b) UASB, (c) ASBR, (d) AFBR

12. Reactor Type Yield mol/mol References
UASB 1.62 Zhao et al. 2008
CSTR 1.84 Show et al. 2007
AFBR 0.4 -1.7 Zhnag et al. 2008
ASBR 0.01-1.0mmol/g
COD
V. Mohan et al 2007
Biohydrogen Yield from different reactors

13. Theoretically
1 mol of glucose can produce 12 mol of H2
C6H12O6 + 12H2O 12H2+ 6CO2
But dark fermentation produces only
4 mol of hydrogen
C6H12O6 + 12H2O CH3COOH+4H2
The maximum efficiency is only 33%.
Further studies express hydrogen yield as
0.47lit/gm of COD when sucrose is used and
0.27lit/gm of COD when glucose is used as substrate

14. The solute of the dark fermentation contains 60-70%
organic acids such as acetate, butyrate, ethanol etc.
These substrate can be converted to methane
2CH3COOH 2CH4 + 2CO2
Integration of dark fermentation followed by methane production
Process Specific yield COD removal
efficiency
Acidogenic Process 16.23 mol H2/kg COD 21.43 kg COD/m3
Methanogenic Process 2.67 mol CH4/kg COD 50.18 kg COD/m3
Source: S. V. Mohan G. Mohankrishna, P. N Sharma (2008). Integration of acidogenic and methanogenic process for
simultaneous production of biohydrogen and methane from waste water, International Journal of Hydrogen Energy ,33pp .
2156-2166

15.  Reduction of waste is enhanced along with the
production of hydrogen and methane
 Inherently more stable
 Ecofriendly, Low-tech, Low capital cost and does not
require inputs of more energy
 Produces valuable metabolites like acetic, butyric and
lactic acid
 High rate of H2 evolution

16.
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