Dr. S. VIJAYA BHASKAR discusses biomethanation and biogas production. Biomethanation is the process where anaerobic bacteria break down organic materials like cow dung and agricultural/municipal waste to produce biogas, a mixture of methane and carbon dioxide. There are two main types of biogas plants - fixed dome plants with a non-movable gas holder, and floating drum plants with a movable gas holder. Biogas can be used for cooking, electricity production, and as a vehicle fuel after removing impurities like carbon dioxide and hydrogen sulfide. The document provides details on the multi-step anaerobic digestion process and substrates used to produce biogas.

1. Dr. S. VIJAYA BHASKAR
M.Tech (Mech., Ph.D (Mgmt), Ph.D (Mech)
PROFESSOR IN MECHANICAL ENGINEERING
Sreenidhi Inst.of Science andTech., Hyderabad

2. UNIT – III
 Biomethanation : Importance of biogas technology,
Different Types of Biogas Plants. Aerobic and anaerobic
bioconversion processes, various substrates used to
produce Biogas (cow dung, human and other agricultural
waste, municipal waste etc.) Individual and community
biogas operated engines and their use.
 Removal of CO2 and H2O, Application of Biogas in
domestic, industry and vehicles. Bio-hydrogen production.
Isolation of methane from Biogas and packing and its
utilization.
B.Tech. (MECHANICAL ENGINEERING) IV Year – I Semester
RENEWABLE ENERGY SOURCES

3. Biogas
 Biogas originates from
bacteria by bio-
degradation of organic
material under anaerobic
(without oxygen)
conditions.
 Biogas typically refers to a
mixture of gases produced
in result of breakdown of
organic matter by the
process of anaerobic
fermentation.

4. Biogas
 The biomass, waste, or waste water feedstocks are
conveyed into the anaerobic digester where a
consortium of natural bacteria feed on the organic
matter producing simpler intermediate compounds
that are eventually
converted to miner-
alized nutrients and
biogas.

5. Biogas
 Methane in atmosphere, from biogenic sources: 90 %
 Methane in atmosphere, from petro-sources: 10%

6. Importance of biogas technology
USES/UTILITIES:
 ENERGY RECOVERY:
 For cooking, lighting, pumping, or power- - with burner,
mantle lamp, engine-pump and generator
 Hygienic disposal of animal waste as manure
 Substitutes for fuelwood & kerosene
 Used in internal combustion engines to power water
pumps & electric generators.

7. Importance of biogas technology
 Energy recovery and reduction of greenhouse
gas [methane] emissions from open Waste Water
Treatment (WWT) ponds gives environmental
benefit also.
 Substitutes for fossil fuels by utilizing methane
generated from the waste.
 The energy generation from industrial
wastewater, with recycling of recovered water has
double benefit in India.

8. Importance of biogas technology

10. Different Types of Biogas Plants
 The division is based on design of Plant and mainly
Two types:
 FIXED DOME (JANATHA) /Const Volume Type Biogas Plant
 FLOATING DRUM /Const Pressure Type Biogas Plant

11. Fixed Dome Type Biogas Plant

12. 1. Mixing tank with inlet pipe and sand trap. 2. Digester.
3. Compensation and removal tank 4. Gasholder.
5. Gaspipe. 6. Entry hatch, with gastight seal.
7. Accumulation of thick sludge. 8. Outlet pipe.
9. Reference level.
10. Supernatant scum, broken up by varying level.

13. Construction -Fixed Dome Type Biogas Plant

14. Working-Fixed Dome Type Biogas Plant

15. Working-Fixed Dome Type Biogas Plant

16. Fixed Dome Type Biogas Plant
 A fixed-dome plant consists of a digester with a fixed,
non-movable gas holder, which sits on top of the
digester.
 Fixed dome plant including gas holder built with Cement
and Brick
 When gas production starts, the slurry is displaced into
the compensation tank.
 The gas is stored in the upper part of the digester.
 Gas pressure increases with the volume of gas stored and
the height difference between the slurry level in the
digester and the slurry level in the compensation tank.

17. Parts
The Main parts of a typical biogas plant consist of the
following components:-
Inlet
Digester
Gas holder
Outlet

18. Parts: Digester
 The digesters of fixed-dome plants are usually
masonry structures, structures of cement and ferro-
cementexist. Main parameters for the choice of
material are:
 Technical suitability (stability, gas- and liquid
tightness);
 cost-effectiveness;
 availability in the region and transport costs;
 availability of local skills for working with the
particular building material.

19. Parts: Gas Holder
 The top part of a fixed-dome plant (the gas space) must be
gas-tight.
 Concrete, masonry and cement rendering are not gas-tight.
 The gas space must therefore be painted with a gas-tight layer
(e.g. 'Water-proofer', Latex or synthetic paints).
 A possibility to reduce the risk of cracking of the gas-holder
consists in the construction of a weak-ring in the masonry of
the digester.
 This "ring" is a flexible joint between the lower (water-proof)
and the upper (gas-proof) part of the hemispherical structure.
 It prevents cracks that develop due to the hydrostatic pressure
in the lower parts to move into the upper parts of the gas-
holder.

20. Advantages
 The costs of a fixed-dome biogas plant are relatively
low.
 It is maintenance is simple as no moving parts exist.
 There are also no rusting steel parts and hence a long
life of the plant (20 years or more) can be expected.

21. DisAdvantages
 Masonry gas-holders require special sealants and
high technical skills for gas-tight construction;
 gas leaks occur quite frequently;
 fluctuating gas pressure complicates gas utilization;
 amount of gas produced is not immediately visible
 plant operation not readily understandable;
 fixeddome plants need exact planning of levels;
 excavation can be difficult and expensive in bedrock.

22. Floating Drum Type Biogas Plant
 Floating-drum plants consist of an underground
digester and a moving gas-holder.
 The gas-holder floats either directly on the
fermentation slurry or in a water jacket of its own.
 The gas is collected in the gas drum, which rises or
moves down, according to the amount of gas stored.
 The gas drum is prevented from tilting by a guiding
frame.
 If the drum floats in a water jacket, it cannot get
stuck, even in substrate with high solid content.

23. Floating Drum Type Biogas Plant

24. Construction

25. Working

26. Working

27. Floating Drum Type Biogas Plant
 Drum - In the past, floating-drum plants were mainly
built in India.
 A floating-drum plant consists of a cylindrical or dome-
shaped digester and a moving, floating gas-holder, or
drum.
 The gas-holder floats either directly in the fermenting
slurry or in a separate water jacket.
 The drum in which the biogas collects has an internal
and/or external guide frame that provides stability and
keeps the drum upright.
 If biogas is produced, the drum moves up, if gas is
consumed, the gas-holder sinks back.

28. Floating Drum Type Biogas Plant

29. Adv and Disadv
Advantages:
 Biogas Supply is Reliable and Consistent
 Pressure is maintained Uniform, because it is called
Const. Pressure type Plant
Disadvantages:

33. Anaerobic bioconversion processes
 Anaerobic Composting occurs in a sealed
oxygen free environment or underwater,
decomposition of the organic materials can lead
to very unpleasant odours due to the release of
sulphur containing compounds such as hydrogen
sulphide, but these slight sulphur odours can
indicate that the decomposition process is working
properly

34. Anaerobic bioconversion processes
 Anaerobic processing of
organic material is a two-
stage process, where
 large organic polymers are
fermented into short-chain
volatile fatty acids.
 These acids are then converted
into methane and carbon dioxide.
The metabolic stages in
biogasification are illustrated in
Figure

35. Anaerobic Bioconversion
 The main feature of anaerobic treatment is the
concurrent waste stabilisation and production of
methane gas, which is an energy source.
 The retention time for solid material in an anaerobic
process can range from a few days to several weeks,
depending upon the chemical characteristics of solid
material
 In the absence of oxygen, anaerobic bacteria decompose
organic matter as follows:
Organic matter + anaerobic bacteria  CH4 + CO2 + H2S
(Hydrogen Sulphide) + NH3 (Ammonia) + other end
products + energy

36. Process

38. The biogas process
■ The complete biological decomposition of organic
matter to methane (CH4) and carbon dioxide (CO2)
under oxygen-depleted conditions (anaerobic) is
complicated and is an interaction between a number of
different bacteria that
are each responsible
for their part of the
task.
■What may be a waste
product from some
bacteria could be a
substrate (or food) for
others, and in this way the bacteria are interdependent.

39. Aerobic and anaerobic
■ Compared with the aerobic (oxygen-rich) decomposition
of organic matter, the energy yield of the anaerobic
process is far smaller.
■The decomposition of, for
example, glucose will
under aerobic conditions
give a net yield of 38 ATP
molecules, while
anaerobic decomposition
will yield only 2 ATP
molecules.
ATP: The Perfect Energy Currency for the Cell
Adenosine tri-phosphate

40. Aerobic and anaerobic
■ This means that the growth rate of anaerobic bacteria
is considerably lower than that of aerobic bacteria and
that the production of biomass (in the form of living
bacteria) is less per
gram decomposed
organic matter.
■Where aerobic
decomposition of 1 g
substance results in the
production of 0.5 g
biomass, the yield under
anaerobic conditions is only 0.1 g biomass.

41. Biogas Steps
■ The biogas process is often divided into three
steps:
■ Hydrolysis,
■ acidogenesis and
■ methanogenesis,
■where different
groups of bacteria are
each responsible for a
step (as it shown in the coming figure).

42. The anaerobic
decomposition of
organic matter
consists of three
main phases:
A.Hydrolysis (1a,
1b, 1c).
B.Acidogenesis,
also called
fermentation (2, 3,
4).
C. Methanogenesis
(5, 6).

43. Hydrolysis
■ During hydrolysis long-chain molecules, such as protein,
carbohydrate and fat polymers, are broken down to monomers
(small molecules).
■ Different specialised
bacteria produce a number
of specific enzymes that
catalyse the decomposition,
and the process is
extracellular – i.e., it takes
place outside the bacterial
cell in he surrounding liquid.

44. Hydrolysis con…
■ Proteins, simple sugars and starch hydrolyse easily
under anaerobic conditions.
■ Other polymeric carbon compounds somewhat more
slowly, while lignin, which is an important plant
component, cannot be decomposed under anaerobic
conditions at all.
■ Cellulose (a polymer composed of a number of
glucose) and hemicellulose (composed of a number of
other sugars) are complex polysaccharides that, are
easily hydrolysed by specialised bacteria.

45. Hydrolysis con…
■ In plant tissue both cellulose and hemicellulose are
tightly packed in lignin and are therefore difficult for
bacteria to get at.
■ This is why only approx. 40% of the cellulose and
hemicellulose in pig slurry is decomposed in the biogas
process.
■ Normally the decomposition of organic matter to
methane and carbon dioxide is not absolute and is
frequently only about 30-60% for animal manure and
other substrates that have a high concentration of
complex molecules.

46. Fermentation – acidogenesis
■ In a balanced bacterial process approximately 50% of the
monomers (glucose, xylose, amino acids) and long- chain
fatty acids (LCFA) are broken down to acetic acid
(CH3COOH).
■ Twenty percent is converted to carbon dioxide (CO2) and
hydrogen (H2), while the remaining 30% is broken down into
short-chain volatile fatty acids (VFA).
■ Fatty acids are monocarboxylic acids that are found in fats.
■ Most naturally occurring fatty acids contain an even
number of carbon atoms.
■ VFAs have fewer than six carbon atoms.
■ LCFAs have more than six carbon atoms.

47. Effects of VFA on fermentation
■ If there is an imbalance, the relative level of VFAs will
increase with the risk of accumulation and the process
“turning sour” because the VFA-degrading bacteria have
a slow growth rate and cannot keep up.
■ A steady degradation of VFAs is therefore crucial and
often a limiting
factor for the biogas
process.

48. Fermentation – acidogenesis
■ Hydrolysis of simple fats results in 1 mol glycerol and 3
mol LCFA.
■ Larger amounts of fat in the substrate will thus result in
large amounts of long-chain fatty acids,
■ while large amounts of protein (that contain nitrogen in
amino groups [-NH2]) will produce large amounts of
ammonium/ ammonia (NH4
+/NH3).
■ In both cases this can lead to inhibition of the subsequent
decomposition phase, particularly if the composition of the
biomass feedstock varies.

49. Methanogenesis
■ The last step in the production of methane is
undertaken by the so-called methanogenic bacteria or
methanogens.
■ The methanogens belong to a kingdom called Archaea,
part of a taxonomic system that also comprises
eukaryotes and bacteria at this level.
■ A kingdom is the highest taxonomic level and Archaea
are therefore at the same level as the other kingdoms –
plants, animals, bacteria (Eubacteria), protozoa and
fungi.
■ Methanogens are believed to have been some of the
first living organisms on Earth.

50. Who is the responsible for methane production?
■ Two different groups of bacteria are responsible for the
methane production.
■ One group degrades acetic acid to methane and the
other produces methane from carbon dioxide and
hydrogen.
■Under stable conditions,
around 70% of the
methane production comes
from the
degradation of acetic acid,
while the remaining 30%
comes from carbon dioxide and hydrogen.

51. Who is the responsible for methane production?
■ The two processes are finely balanced and inhibition of one
will also lead to inhibition of the other.
■ The methanogens have the slowest growth rate of the
bacteria involved in the process, they also become the
limiting factor for how quickly
the process can proceed and
how much material can be
digested.
■ The growth rate of the
methanogens is only around
one fifth of the acid-forming
bacteria.

52. ■ As previously mentioned, the methanogens do not
release much energy in the process (as it shown in the
coming table).
■But due to the anoxic
conditions, the
competition from other
bacteria is limited,
which is why they
manage to survive.

53. Energy yield of methanogens from decomposition
of different sources.

54. Anaerobic bioconversion processes

55. Anaerobic bioconversion processes

56. Anaerobic bioconversion processes

57. Anaerobic bioconversion processes
Advantages and Disadvantages:

58. Aerobic bioconversion processes
 Aerobic sludge digestion is a biological process
that takes place in the presence of oxygen. With
oxygen, bacteria present in the sludge (activated
sludge) consumes organic matter and converts it
into Methane, carbon dioxide, etc.

59. Aerobic bioconversion processes

60. Adv & Disadv: Aerobic bioconversion

61. Various substrates used to produce Biogas

62. Individual and community biogas operated
engines and their use

63. Individual and community biogas operated
engines and their use
Biogas gas-grid injection
Biogas in transport
Using of carbon dioxide and methane as
chemical products

64. Uses

65. Biomethanation
Part-B
R E M O V A L O F C O 2 A N D H 2 O
A P P L I C A T I O N O F B I O G A S I N D O M E S T I C ,
I N D U S T R Y A N D V E H I C L E S .
B I O - H Y D R O G E N P R O D U C T I O N .
I S O L A T I O N O F M E T H A N E F R O M B I O G A S A N D
P A C K I N G A N D I T S U T I L I Z A T I O N .

66. Formation of Biogas
Organic matter + anaerobic bacteria 
CH4 + CO2 + H2S (Hydrogen Sulphide) +
NH3 (Ammonia) + other end products +
energy

67. Removal of CO2 from Biogas
Water scrubbing
 Carbon dioxide is soluble in water.
 Water scrubbing uses the higher solubility of CO2
in water to separate the CO2 from biogas.
 This process is done under high pressure and
removes H2S as well as CO2.
 The main disadvantage of this process is that it
requires a large volume of water that must be
purified and recycled
Carbonic acid

69. Removal of CO2
Polyethylene glycol scrubbing
This process is similar to water
scrubbing; however, it is more
efficient.
It also requires the regeneration of a
large volume of polyethylene
glycol.

70. Pressure Swing Adsorption (PSA)
Aka Carbon molecular sieves
 The carbon molecular sieve
method uses differential
adsorption characteristics to
separate CH4 and CO2.
 This adsorption is carried out
at high pressure and is also
known as pressure swing
adsorption.
 For this process to be
successful, H2S should be
removed before the adsorption
process. Zeolites Used

71. Pressure swing adsorption
 A typical PSA system is composed of four vessels in series
that are filled with adsorbent media which is capable of
removing water vapor, CO2, N2 and O2 from the biogas
stream.
 During operation, each adsorber operates in an alternating
cycle of adsorption, regeneration and pressure build-up.
 Dry biogas enters the system through the bottom of one of
the adsorbers during the first phase of the process. When
passing through the vessel, CO2, N2 and O2 are adsorbed
onto the surface of the media. The gas leaving the top of the
adsorber vessel contains more than 97% CH4
Adsorption is the adhesion of atoms, ions or molecules
from a gas, liquid or dissolved solid to a surface.

72. Absorption and Adsorption
Adsorption is the adhesion of
atoms, ions or molecules
from a gas, liquid or dissolved
solid to a surface.

73. Membrane separation
There are two membrane separation techniques:
• high pressure gas separation
• gas-liquid adsorption
 The high pressure separation process selectively
separates H2S and CO2 from CH4.
 Usually, this separation is performed in three
stages and produces 96 per cent pure CH4.

74. Membrane separation

75. 75
What is a membrane?
A membrane is a physical device able to separate
selectively one ore more components in a mixture
while rejecting others.
Feed side
Permeate side
Perm-selective Membrane
Permeation

76. Removal of CO2
 Gas liquid absorption is a new development and
uses microporous hydrophobic membranes as an
interface between gas and liquids.
 The CO2 and H2S dissolve while the methane (in the
gas) is collected for use.

77. Cryogenics Separation
 CO2 can be separated from other gases by cooling
and condensation.
 Cryogenic separation is widely used commercially for
streams that already have high CO2 concentrations
(typically >90%) but it is not used for more dilute
CO2 streams

78. Transport mechanism through POROUS
membranes
Knudsen flow
Surface diffusion
Capillar condensation
Viscous flow
H. Strathmann, L. Giorno, E. Drioli, An introduction to membrane science and
technology, Publisher CNR Roma, ISBN 88-8080-063-9, 2006

79. Removal of H2O/Water Vapour
 Biogas generated from anaerobic digestion is usually
saturated with water vapor.
 Water vapour may condense into water or ice and thus
result in corrosion and clogging issues.
 Most biogas utilization processes require relatively dry
gas, so removal of water vapor is required.
Passive cooling:
 Biogas pipe line is run though underground for a short
period of time.
 Water condenses from the biogas as it cool down.
 The condensate either discharges to sewer or recycle
back.

80. Removal of H2O/Water Vapour
Refrigeration and Pressurization:
 Heat exchangers can be used to cool down the biogas
so that the water vapour gets condensed. Biogas can
be further pressurized to dry it more.
Absorption:
 Biogas can be passed through drying medium like
glycol, hygroscopic salts, silica gel, aluminum
oxide etc. to absorb water.
 These drying medium can be regenerated by drying
them at high temperature and sometime at high
pressure as well. Eventually the drying media has
to be replaced.

81. FYI: High-Level Removal Process

82. Application of Biogas in domestic, industry
and vehicles

83. Application of Biogas in domestic, industry
and vehicles

84. Application of Biogas in domestic, industry
and vehicles

85. Bio-hydrogen production
Hydrogen is a valuable gas as a clean energy source and as
feed stock for some industries.
 It is a non-pollutant gas in environment.
 Therefore demand on hydrogen production has
increased considerably in recent years.
 Hydrogen gas is a high energy ( 122 KJ/g) clean fuel
which can be used for many different purposes.
 Biomass and water can be used as renewable resources
for hydrogen gas production.

86. Bio-hydrogen production
 Electrolysis of water
 Steam reforming of hydrocarbons
 Auto-thermal process
 Biological process are
 (a) bio-photolysis of water by algae
 (b) dark fermentation
 (c) photo fermentation

87. Bio-hydrogen production
 Electrolysis of water
 Steam reforming of hydrocarbons
 Auto-thermal process
 Biological process are
 (a) bio-photolysis of water by algae
 (b) dark fermentation
 (c) photo fermentation

88. Electrolysis of Water
 Electrolysis of water may be the cleanest technology
for hydrogen gas production.
 However, electrolysis should be used in areas where
electricity is inexpensive since electricity costs account
for 80% of the operating cost of H2 production.
 In addition, feed water has to be demineralized to
avoid deposits on the electrodes and corrosion.

89. Setup of H2 Preparation
 An electrical power source is connected to two
electrodes, or two plates (typically made from some
inert metal such as platinum or stainless steel)
which are placed in the water.
• Hydrogen will appear
at the cathode (the -
vely charged electrode,
where electrons enter
the water), and oxygen
will appear at the anode
(the +vely charged
electrode).

90. Electrolysis of Water
 Assuming ideal faradic efficiency, the amount of
hydrogen generated is twice the number of moles
of oxygen, and both are proportional to the total
electrical charge conducted by the solution.
2 H2O(l) → 2 H2(g) + O2(g)
 However, in many cells competing side reactions
dominate, resulting in different products and less
than ideal faradic efficiency.

91. Electrolysis of Water
 Electrolysis of pure water requires excess energy in the
form of over potential to overcome various activation barriers.
 Without the excess energy the electrolysis of pure water
occurs very slowly or not at all.
 This is in part due to the limited self-ionization of water.
 Pure water has an electrical conductivity about one millionth
that of seawater.
 Many electrolytic cells may also lack the requisite electro
catalysts.
 The efficacy of electrolysis is increased through the addition of
an electrolyte (such as a salt, an acid or a base) and the use of
electro catalysts.

92. Chemical Reaction
Reduction at cathode: 2 H+(aq) + 2e− → H2(g)
Anode (oxidation): 2 H2O(l) → O2(g) + 4 H+(aq) + 4e−
Cathode (reduction): 2 H2O(l) + 2e− → H2(g) + 2 OH- (aq)
Overall reaction: 2 H2O(l) → 2 H2(g) + O2(g)

93. Steam reforming of hydrocarbons
 Steam reforming of natural gas or syngas sometimes
referred to as steam methane reforming (SMR) is the
most common method of producing commercial bulk
hydrogen as well as the hydrogen used in the industrial
synthesis of ammonia.
 It is also the least expensive method.
 At high temperatures (700 – 1100 °C) and in the
presence of a metal-based catalyst (nickel),
steam reacts with methane to yield carbon
monoxide and hydrogen.
 These two reactions are reversible in nature.
CH4 + H2O → CO + 3 H2

94.  Additional hydrogen can be recovered by a lower-
temperature gas-shift reaction with the carbon
monoxide produced.
 The reaction is summarized by:
CO + H2O → CO2 + H2
The first reaction is strongly endothermic
(consumes heat).
the second reaction is mildly exothermic
(produces heat).
The efficiency of the process is approximately 65% to
75%.
Steam reforming of hydrocarbons

95.  Auto thermal reforming (ATR) uses oxygen and carbon
dioxide or oxygen and steam in a reaction with
methane to form syngas.
 The reaction takes place in a single chamber where the methane
is partially oxidized.
 The reaction is exothermic due to the oxidation.
 When the ATR uses carbon dioxide the H2:CO ratio produced is 1:1;
when the ATR uses steam the H2:CO ratio produced is 2.5:1
 The reactions can be described in the following equations, using
CO2:
2CH4 + O2 + CO2 → 3H2 + 3CO + H2O
 And using steam:
4CH4 + O2 + 2H2O → 10H2 +4CO
AUTO THERMAL REFORMING

96.  The outlet temperature of the syngas is between 950-
1100 C and outlet pressure can be as high as 100 bar.
 The main difference between SMR and ATR is that
SMR uses no oxygen. The advantage of ATR is that
the H2:CO can be varied, this is particularly useful for
producing certain second generation biofuels, such
as DME which requires a 1:1 H2:CO ratio.
AUTO THERMAL REFORMING

97.  Biological hydrogen production stands out as an
environmentally harmless process carried out under
mild operating conditions, using renewable
resources.
 Several types of microorganisms such as the
photosynthetic bacteria, cyanobacteria, algae
or fermentative bacteria are commonly
utilized for biological hydrogen production
Algae split water molecules to hydrogen ion and oxygen via photosynthesis.
BIOLOGICAL PRODUCTION

98. Biological hydrogen production
Biological production of hydrogen is carried out using microorganisms in an
aqueous environment at particular temperature and pH. However, the yield of hydrogen
production is low as compared to other conventional methods but there is reduced
emission of greenhouse gases (GHGs) by 57–73 per cent using biological methods.
Among different hydrogen production methods, biological methods are of great importance
as they are less energy intensive.
Methods of Bio hydrogen Production:
a. Direct Photolysis (algae)
b. Indirect Photolysis ( cyano- bacteria)
c. Dark Fermentation
d. Photo Fermentation

99. Overview of currently known biological hydrogen
production processes

100. FYI: Additional Information
 Bio-Hydrogen production

101.  Algae split water molecules to hydrogen ion and
oxygen via photosynthesis.
 The generated hydrogen ions are converted into
hydrogen gas by hydrogenase enzyme.
 Chlamydomonas reinhardtii is one of the well-known
hydrogen producing algae .
 Hydrogenase activity has been detected in green
algae, Scenedesmus obliquus,in marine green algae
Chlorococcum littorale.

102.  The capital cost of steam reforming plants is
prohibitive for small to medium size applications
because the technology does not scale down well.
 Conventional steam reforming plants operate at
pressures between 200 and 600 psi with outlet
temperatures in the range of 815 to 925 °C.
 However, analyses have shown that even though it is
more costly to construct, a well-designed SMR can
produce hydrogen more cost-effectively than an ATR.

103.  Biological hydrogen production stands out as an
environmentally harmless process carried out under
mild operating conditions, using renewable resources.
 Several types of microorganisms such as the
photosynthetic bacteria, cyanobacteria, algae or
fermentative bacteria are commonly utilized for
biological hydrogen production

104.  Algae split water molecules to hydrogen ion and
oxygen via photosynthesis.
 The generated hydrogen ions are converted into
hydrogen gas by hydrogenase enzyme.
 Chlamydomonas reinhardtii is one of the well-known
hydrogen producing algae .
 Hydrogenase activity has been detected in green
algae, Scenedesmus obliquus,in marine green algae
Chlorococcum littorale.

105.  The algal hydrogen production could be considered as
an economical and sustainable method in terms of
water utilization as a renewable resource and CO2
consumption as one of the air pollutants.
 However, strong inhibition effect of generated oxygen
on hydrogenase enzyme is the major limitation for the
process.
 Low hydrogen production potential and no waste
utilization are the other disadvantages of hydrogen
production by algae.

106.  During dark fermentation, sugars are converted to
H2, CO2 and short-chain organic acids with a
theoretical maximum hydrogen yield of FOUR
moles of H2/mole of hexose sugar, when all sugars
are fermented to acetate, CO2 and H2.

107. Isolation of Methane from Biogas

108. What is biogas?
■ Biogas is a combustible
mixture of gases.
■ It consists mainly of
methane (CH4) and
carbon dioxide (CO2) and
is formed from the
anaerobic bacterial
decomposition of organic
compounds, i.e. without
oxygen. The actual make-up depends on what
.is being decomposed

109. Properties of Methane
■ Methane makes up the combustible part of biogas.
■ Methane is a colourless and odourless gas with a boiling
point of -162°C and it burns with a blue flame.
■ Methane is also the main constituent (77-90%) of natural
gas.
■Chemically, methane
belongs to the alkanes
and is the simplest
possible form of these.

110. Isolation of Methane from Biogas

111. Biogas Storage
Schematic of on-farm storage system for compressed bio-
methane

112. Distribution as Vehicle Fuel
• Usually biomethane is transported to the filling stations via public
gas pipelines.
• Alternatively, it can be transported by trucks in high-pressure
gas bottles or directly used at a filling station at the location of
biomethane production.
• Biomethane can also be supplied and used as fuel in the form of
liquefied biogas (LBG or bio-LNG).
• Biomethane must reach certainquality requirements
for methane and water vapor content to be transported by
trucks (98% Methane-10ppm water ).

113. Storage and Distribution
 Clean Methane gas filled into
a standard CNG bottle
 The cleaned Methane gas is
than taken into a 3-Stage
high-pressure compressor.
 The compressor compresses
the gas from
Stage I: Atmospheric to 10Kg/cm2
Stage II: 10Kg/cm2 to 60Kg/cm2
Stage III: 60Kg/cm2 to 250Kg/cm2

114. Storage and Distribution
 This pressure is considered suitable to fill up a CNG
bottle rack. This CNG Bottle Rack can than be
connected to a standard CNG Dispenser unit.
 Now this purified Gobar gas is ready to be used as
Fuel in a motor car, or run a Gas Turbine or any
CNG converted Internal combustion engine
connected to an alternator to produce electricity.

115. Biogas vehicle configuration
• A gasoline car can quite easily be converted into bio-fuel gas
operation by adding a second fuel supply system and storage
cylinders for methane.
• A dedicated gas engine means a spark-ignited engine that is
converted to run on gas only and offers Higher compression
ratio than a standard gasoline engine.
• Dual-fuel engines, which use diesel fuel and gas
simultaneously, hold a promise of diesel-like efficiency and
power output but drawback of unburned methane
emission.