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BIO-
GAS
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| Biogas
is a mixture of methane (CH4), carbon dioxide (CO2), and depending
on the feedstock used, trace gases such as nitrogen, ammonia
(NH3), sulfur dioxide (SO2), hydrogen sulfide (H2S), and hydrogen
Methane is the main component of biogas. It is relatively clean
burning, colorless, and odorless. Biogas is basically the same
as natural gas which is 'dried' and treated, removing the trace
gases, then piped to homes for cooking and heating. This is
already being done on a large scale in some countries of the
world Biogas is produced when certain bacteria decompose organic
material in an anaerobic (no oxygen is present) environment.
This process is referred to as anaerobic digestion (AD). AD
is a proven technology for effectively treating the organic
fraction of waste. The treatment of waste through AD has many
benefits; it leads not only to a cleaner and healthier environment,
but also produces a renewable energy source, methane. The by-product,
a solid residue is high-grade manure. The Biogas plants are
the cheap sources of energy in rural areas. |
| Animals that eat a
lot of plant material, particularly grazing animals such as
cattle, produce large amounts of biogas. The biogas is produced
not by the cows themselves, but by billions of microorganisms
living in their digestive systems. Biogas also develops in bogs
and at the bottom of lakes, where decaying organic matter builds
up under wet and anaerobic conditions. Besides being able to
live without oxygen, methane-producing microorganisms have another
special feature: They are among the very few creatures that
can digest cellulose, the main ingredient of plant fibers. Another
special feature of these organisms is that they are very sensitive
to conditions in their environment, such as temperature, acidity,
the amount of water, etc. |
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Component
|
Symbol
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Percentage
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| Methane |
CH4
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40-70
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| Carbon dioxide |
CO2
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30-60
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| Hydrogen |
H2
|
1.0
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| Nitrogen |
N2
|
0.5
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| Carbon monoxide |
CO
|
0.1
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| Oxygen |
O2
|
0.1
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| Hydrogen sulphide |
SH2
|
0.1
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| Biogas is a good fuel.
Have you thought how this is formed? Biomass like animal excreta,
vegetable wastes and weeds undergo decomposition in the absence
of oxygen in a Biogas plant and form a mixture of gases. This
mixture is the biogas. Its main constituent is methane. This
is used as a fuel for cooking and lighting. |
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Biogas
is a Form of Renewable Energy
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Flammable
biogas can be collected using a simple tank, as shown here.
Animal manure is stored in a closed tank where the gas accumulates.
It makes an excellent fuel for cook stoves and furnaces, and
can be used in place of regular natural gas, which is a fossil
fuel.
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| Biogas is considered
to be a source of renewable energy. This is because the production
of biogas depends on the supply of grass, which usually grows
back each year. By comparison, the natural gas used in most
of our homes is not considered a form of renewable energy. Natural
gas formed from the fossilized remains of plants and animals-a
process that took millions of years. These resources do not
"grow back" in a time scale that is meaningful for
humans. |
| Biogas
is formed by the process known as anaerobic digestion (AD) which
basically means decomposition in the absence of oxygen. Anaerobic
digestion occurs naturally wherever high concentrations of wet
organic matter accumulate in the absence of dissolved oxygen.
Under these conditions several types of bacteria work together
to break down organic matter releasing gas which can then be
stored and used as energy. |
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The bacteria thrive on organic mater
and break down proteins, carbohydrates, cellulose and fats
into low molecular compounds producing organic acids, carbon
dioxide, hydrogen sulphide and ammonia. Further bacteria cultures
process this mixture into carbon dioxide, alkaline water and
methane - the valuable component of biogas. The whole process
takes place inside a biogas fermenter, as pictured.
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| The bacteria cultures
which break down organic matter like to be warm, so an efficient
anaerobic digester must be heated to maintain optimal levels
for their survival. It must also be stirred to ensure the bacteria
receive sufficient food (organic waste) to survive and procreate,
if conditions deteriorate the culture may die. The mixing and
heating elements are shown in this picture from inside the fermenter. |
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Benefits
of Biogas
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| Processing organic
waste anaerobically to create Biogas is a sustainable, renewable
waste to energy solution. The process offers numerous advantages
over conventional technologies: |
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Production of electricity and
heat provides valuable income
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| •
Reduced land fill TAX & climate
change levy charges |
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Income from ROCs certificates
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Fermented digestate retains good fertiliser properties with
more available nitrogen, improved homogeneity and a markedly
reduced odour
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•
Improvement in slurry characteristics such as: fluidity, crop
compatibility, homogeneity, reduction of weed germs and reduction
of odours
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•
Reduced environmental impacts (by replacing fossil fuels:
Biogas powers the bus above in Lille, France)
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A closed carbon dioxide cycle reduces atmospheric pollution
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•
Positive use of organic waste materials reduces land and water
pollution
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•
Reduced use of chemical fertilisers minimises leaching from
soil
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Waste
Processing
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The main advantage of anaerobic digestion,
other than the creation of valuable methane, is its ability
to process organic waste. Up to half of all the rubbish we
throw in landfills could be processed in this way, significantly
reducing our burden on the environment.
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Obvious applications for biogas waste
processing systems involve farms and livestock where the generation
of slurry and other organic wastes is of sufficient volume
to run a system efficiently andutilise the resultant heat
or power.
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Biogas
systems
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| The Substrate
inputs like slurry, dry manure from cattle, pigs and poultry,
raw materials such as corn or grass, organic waste including
fats, vegetables and catering waste enter the fermenter where
it is mixed, heated and agitated. Methane bacteria decompose
the organic compounds and produce biogas and the processed digestate
is separated for use as a natural fertiliser. The biogas is
then piped to a CHP (GKHW) unit comprising a combustion engine
and electrical generator where it is converted into heat and
electricity. |
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