Presented by:
Alisha Khadka
Angila Chaulagain
Susma Poudel
Biogas is the gases produced by anaerobic digestion
of organic matter.
Biogas is produced after organic materials (plant and
animal products) are broken down by bacteria in an
oxygen-free environment, a process called anaerobic
digestion. Biogas systems use anaerobic digestion to recycle
these organic materials, turning them into biogas, which
contains both energy (gas), and valuable soil products
(liquids and solids).
It is a mixture of: –
• Methane (CH4)
• Carbon dioxide (CO2)
• Hydrogen (H2)
• Hydrogen sulphide (H2S)
The chief constituent of biogas is methane (65%).
Biogas Engineering
Biogas engineering is the practice of
engineering arts, to produce biogas through
the breakdown of organic matter in the
absence of oxygen.
Importance of Biogas Engineering
-Non-polluting source of energy
-Renewable sources of energy.
-Efficient way of energy conversion.
-Saves lives of women and children.
-Produces enriched organic manure which can
supplement or even replace chemical fertilizers.
-Provides a source for decentralized power generation.
-Lead to improvement in the environment, sanitation
and hygiene.
-Lead to employment generation in the rural areas.
-Household wastes and bio-wastes can be disposed of
usefully and in a healthy manner.
-The technology is cheaper & much simple than those for
other bio-fuel.
-Any biodegradable matter can be used as substrate.
-Anaerobic digestion inactivates pathogen & parasites. It
is quite effective in reducing the incidence of water
borne diseases.
-Environment benefit on a global scale.
How it work
• Anaerobic digestion- absence of oxygen, aka
fermentation
• Organic waste is put in a air tight chamber to
keep oxygen from entering
• Plant, animal and fecal matter typical
• Methane, Carbon dioxide, Hydrogen sulphide
formed
Conventional Biogas
• In conventional biogas plant, biogas is produced by
anaerobic digestion with anaerobic bacteria or
fermentation of biodegradable materials such as manure,
sewage, municipal waste, green waste, plant material,
and crops.
• Gas produced is primarily methane (CH4) and carbon
dioxide (CO2) and may have small amounts of hydrogen
sulphide (H2S), moisture and siloxanes.
There are two types of conventional biogas
plant :
• Fixed dome biogas plant
• Floating drum biogas plant
Construction
The biogas plant is a brick and cement structure
having the following five sections:
• Mixing tank present above the ground level.
• Inlet tank: The mixing tank opens underground
into a sloping inlet chamber.
• Digester: The inlet chamber opens from below
into the digester which is a huge tank with a
dome like ceiling. The ceiling of the digester has
an outlet with a valve for the supply of biogas.
• Outlet tank: The digester opens from below into
an outlet chamber.
• Overflow tank: The outlet chamber opens from
the top into a small over flow tank.
working
• The various forms of biomass are mixed with an
equal quantity of water in the mixing tank. This
forms the slurry.
• The slurry is fed into the digester through the inlet
chamber.
• When the digester is partially filled with the slurry,
the introduction of slurry is stopped and the plant is
left unused for about two months.
• During these two months, anaerobic bacteria
present in the slurry decomposes or ferments the
biomass in the presence of water.
• As a result of anaerobic fermentation, biogas is
formed, which starts collecting in the dome of the
digester.
• As more and more biogas starts collecting, the
pressure exerted by the biogas forces the spent
slurry into the outlet chamber.
• From the outlet chamber, the spent slurry overflows
into the overflow tank.
• The spent slurry is manually removed from the
overflow tank and used as manure for plants.
• The gas valve connected to a system of pipelines is
opened when a supply of biogas is required.
• To obtain a continuous supply of biogas, a
functioning plant can be fed continuously with the
prepared slurry.
Advantages
• Relatively low construction costs.
• The absence of moving parts and rusting steel parts.
• If well constructed, fixed dome plants have a long life
span.
• The underground construction saves space and protects
the digester from temperature changes.
• The construction provides opportunities for skilled local
employment.
Disadvantages
• Fluctuating gas pressure complicates gas utilization.
• Amount of gas produced is not immediately visible.
• Fixed dome plants need exact planning of levels.
• Excavation can be difficult and expensive in bedrock.
The floating gas holder type bio gas plant consists of
a dome shaped gas holder made of steel for
collecting bio gas. The dome shaped gas holder is
not fixed but is moveable and floats over the slurry
present in the digester tank. Due to this reason, this
biogas plant is called floating gas holder type biogas
plant.
Slurry is prepared by mixing water in cattle dung in
equal proportion in mixing tank. The slurry is then
injected into a digester tank with the help of inlet
pipe. The digester tank is a closed underground tank
made up of bricks. Inside the digester tank, the
complex carbon compounds present in the cattle
dung breaks into simpler substances by the action of
anaerobic microorganisms in the presence of water.
This anaerobic decomposition of complex carbon
compounds present in cattle dung produces bio gas and
gets completed in about 60 days. The bio gas so produced
starts to collect in floating gas holder and is supplied to
homes through pipes. And the spent slurry is replaced
from time to time with fresh slurry to continue the
production of bio gas.
Advantages
• Simple, easily understood operation - the volume
of stored gas is directly visible.
• The gas pressure is constant, determined by the
weight of the gas holder.
• The construction is relatively easy
• Construction mistakes do not lead to major
problems in operation.
Disadvantages
• High material costs of the steel drum,
• Susceptibility of steel parts to corrosion.
• Because of this, floating drum plants have a
shorter life span than fixed-dome plants and
regular maintenance costs for the painting of the
drum.
Nisargruna Biogas plant
NISARGRUNA Biogas plant is a medium to larger scale
Biogas plant which is able to process biodegradable waste
such as kitchen waste, paper, grass, gobar and dry leaves.
It offers Zero garbage and Zero effluent and provides high
quality manure and methane gas. Weed-free manure
obtained from such waste has high nitrogen contents and
acts as an excellent soil conditioner.
• This plant could be set up for eco-friendly disposal of
wet-waste generated in kitchens/canteens of big
Hospitals/Hotels/Factories/residential complexes and
can avoid health hazards due to dump sites.
This technology of biphasic bio-methanation has high
potential of solving the solid waste management
problems of the urban areas and provides organic
manure and bio-gas as a fuel.
ADVANTAGES
Nisargruna Bio Gas Plant would serve many purposes such as:-
• Environment friendly disposal of waste.
• Generation of fairly good amount of fuel biogas, which will
definitely support the dwindling energy resources.
• Generation of high quality, weed free manure, which is an excellent
soil conditioner. This is very important for replenishing organic
carbon in the undernourished soil after years of agriculture.
Reference
• https://www.slideserve.com/cara/biogas-digester/?utm_source=slide
serve&utm_medium=website&utm_campaign=auto+related+load
• https://www.slideserve.com/elizabeth-whitley/biogas
• https://energypedia.info/wiki/Floating_Drum_Biogas_Plants
• https://
sswm.info/sites/default/files/reference_attachments/ISAT%20GTZ%2
01999%20Biogas%20digest%20Volume%20II%20Biogas%20Applicatio
n%20and%20Product%20Development.pdf
• https://
www.eesi.org/papers/view/fact-sheet-biogasconverting-w
aste-to-energy
• https://www.pluginindia.com/nisargrunabiogasplant.html
• https://www.slideshare.net/arpitsaraf21/biogas-traditiona
l-vs-modern-plant
• https://www.slideshare.net/asertseminar/biogas-ppt
• https://www.gasum.com/en/our-operations/biogas-
production/how-is-biogas-produced/
