Biogas is produced by the breakdown of organic waste by bacteria during anaerobic digestion. It is a mixture of gases, primarily methane and carbon dioxide. A biogas plant consists of a digester where the waste decomposes and a gas holder that captures the gases produced. Biogas can be used as a fuel for cooking, lighting, electricity generation, and transportation. While biogas has benefits such as being renewable and reducing pollution, some challenges to biogas adoption include plant failures and lack of technology advancement to produce cleaner gas.

1. Environmental Sustainability through Greening the industries-2017
Biogas
Technology
Ruwan Wijemanne
Energy Expert- NCPC

2. ‘GOOD’ or ‘BAD’?
Sort these FUELS from BEST to WORST.
Methane
Coal
The Wind
Cow dung
A banana skin
A tree
Sunshine
A waterfall
Furnace oil
Uranium
GOOD
BAD

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Also known as…
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……(A mixture of gases)
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Biogas
Find out …
What is it made from?
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4. Content
• Biomass as an energy source
• Biogas Generation
• Technical variants
• Applications

5. Introduction
What is Biogas?
• Most organic matter begins the process of
decomposition when it is exposed to oxygen and
sunlight.
• However, organic matter can also decompose
without any oxygen, by the process of anaerobic
fermentation.
• This happens due to the bacteria present in the
matter which acts during the absence of oxygen.

6. What is biogas?
• A mixture of methane and
carbon dioxide
CH4
CO2
• Methane or ‘swamp gas’,
produced naturally in
swampy ponds
What is this?

7. • It can also be captured from landfill sites where
organic waste has been rotting under the ground

9. • Landfills see a lot of such decay, especially
when the waste material becomes wet and
receives little sunlight.
• As a result, a lot of methane and nitrous oxide
is produced and released into the atmosphere.
• Biogas is the result of this decay, and it is an
energy source like no other.

10. In other words
• Biogas typically refers to a mixture of
different gases produced by the breakdown
of organic matter in the absence of oxygen.
• Biogas can be produced from raw materials
such as agricultural waste, manure, municipal
waste, plant material, sewage, green waste or
food waste.
• It is a renewable energy source and in many
cases exerts a very small carbon footprint.

11. • Biogas can be produced by anaerobic
digestion with anaerobic bacteria, which
digest material inside a closed system, or
fermentation of biodegradable materials

12. • Biogas is primarily methane (CH4) and carbon
dioxide (CO2) and may have small amounts of
hydrogen sulfide (H2S), moisture and siloxanes.
• The gases methane, hydrogen, and carbon
monoxide (CO) can be combusted or oxidized
with oxygen.
• This energy release allows biogas to be used as
a fuel; it can be used for any heating purpose,
such as cooking.
• It can also be used in a gas engine to convert the
energy in the gas into electricity and heat.

13. Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may
have small amounts of hydrogen sulfide (H2S), moisture and siloxanes.
Calorific Value: 21 MJ/kg (37 MJ/m3)

14. History of Biogas
1808 – Sir
Humphrey Davy
found that
methane was
present in the
gases that is
formed by the
Anaerobic
Digestion of
manure
1884 – Louis
Pasteur student,
Ulysse Gayon,
performed the
anaerobic
fermentation of
manure and
water at 35ºC
and obtained
100 liters of
Biogas per cubic
meter of
Manure.
1895 – Biogas is
used to light up
the streets in
Exeter, England
1957 – A British
Inventor, Bates,
modifies his car
to run on Biogas
produced from
pig manure.
2005 – The
Biogas Support
program in
Nepal wins the
Ashden Reward
for installing
over 150,000
Biogas Plants in
rural areas. And
a Biogas
powered train
starts it's service
in Sweden

15. What is it used for?
• Biogas is a fuel used as an energy source for light or heat

16. What is it used for?
• Biogas is a fuel used as an energy source for light or
heat
• Cooking 0.2 m3/of biogas per person/day
• 1 lamp 0.15 m3/of biogas per hour
• engines 0.7 m3/of biogas per kWh
• Refrigeration
• Transportation

17. Advanced applications
• Biogas is a fuel used as an energy source for electricity
generation

18. Advanced applications
• Biogas can be compressed, the same way natural
gas is compressed to CNG, and used to power
motor vehicles.
• In the UK, for example, biogas is estimated to
have the potential to replace around 17% of
vehicle fuel.
• It qualifies for renewable energy subsidies in
some parts of the world.
• Biogas can be cleaned and upgraded to natural
gas standards, when it becomes bio methane

19. Biogas is produced by the breakdown of organic
waste by bacteria without oxygen (anaerobic
digestion or fermentation).
How is it made?
Leftover food from houses,
shops, restaurants and factories
Cow, sheep and
chicken manure Sewage
Leftover meat and
blood from
abattoirs
Leftover straw and
crops from farming
What types of organic waste could be
turned in biogas?

20. Water, Excreta,
Organic Material,
Biodegradable Waste
Hydrolysis, Fermentation,
Acetogenesis,
Dehydrogenization,
Methanogenesis
Methane
CO2
Amonio
H2SBiogas
Anaerobic Environment
Water with 80-90%
less contaminants,
Organic Fertilizer
O2
Graphic courtesy of Raul Botero
ENERGY+
(3)

21. The Main parts of a typical biogas plant consist of the
following components:-
• Inlet
• Digester
• Gas holder
• Outlet
There are different types of biogas production plants . The
main two types are as follows :-
• Fixed-dome Plant
• Floating-drum Plants
Biogas Plant

22. What is biogas plant?
• A biogas plant is an anaerobic digester that
produces biogas from animal wastes or energy
crops.
• Energy crops are cheap crops grown for the
purpose of biofuels, rather than food.
• Biofuels are liquid, gaseous, or solid fuel made
from live or recently dead organic material known
as biomass, as opposed to fossil fuels, which are
composed of ancient biological materials.

23. • Biogas is a type of biofuel created via
anaerobic, or oxygen-free, digestion of organic
matter by bacteria.
• A biogas plant is composed of a digester and a
gas holder.

24. What is a digester?
• The digester is an airtight container in which
the waste is dumped and decomposed, and
the gas holder is a tank that harnesses the
gases emitted by the slurry.
• Bacteria within the digester tank breaks
down the waste and, as it decomposes, gases
such as carbon monoxide, methane,
hydrogen, and nitrogen, are released.

25. • Through a pressurized system, the gas holder
conducts the flow of these gases upward into a
hole in its drum.
• The hole is specially designed to allow gases to
pass freely into the holder while prohibiting any
gases from escaping back into the digester.
• In a controlled environment, the gases are later
combusted, or reacted, with oxygen to create an
energy source for such processes as heating and
vehicle propulsion

26. Biogas is made by fermenting organic waste in a biogas
digester.
Digesters vary from small household systems…
How is it made?

27. Lankan Dry Batch Biogas
System
• Batch type
• Straw, cow dung, Urea
• 2 weeks for growing media
• 6 months retention time
• 4 months retention for
vegetable/ food waste
• Need to fill 2/3 of Digester
• Sludge is a good fertilizer

28. Chinese type biogas system
• Domestic food waste
• Continuous type
• Fixed dome
• Channelling prevention wall

29. Fixed dome type
• A fixed-dome plant consists of a digester with a fixed, non-movable gas
holder, which sits on top of the digester
• Advantage - The costs of a fixed-dome biogas plant are relatively low. It 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.

30. Chinese type biogas system

31. Plug flow type biogas system
• Wet type
• Market garbage
• Continuous type
• Fixed dome

32. Floating dome type

33. Floating dome type
• 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
• Advantage- Floating-drum plants are easy to understand and
operate. They provide gas at a constant pressure, and the stored
gas-volume is immediately recognizable by the position of the drum.

34. Floating dome type

35. Sausage Bag Gas Plant
Sludge used as a
fertiliser
Gas to kitchen
Quick to construct
May require importing
May require protection from sharp
objects & vermin
Material is polyethylene plastic

36. Sausage Bag Gas Plant

37. Domestic Gas Plant

38. • Qty of substrate (feed rate)
• Assess the biogas yield
• Plan for usage
• Size of components
• Location
• Cost
Biogas Generation – Design

39. • Qty of substrate (feed rate)
Biogas Generation – Design
Source Kg/day per animal Gas yield (l/kg)
Cow 10 37
Buffalo 15 37
Human excreta 0.4 70
Pig 2.25 80
Poultry 0.18 61
• Digester selection
Digester volume
m3
Waste needed
Kg/day
Gas yield
(m3/day)
6 25 1.5
8 50 2
10 75 2.5
12 100 3
• Size of digester for cattle field
with 7 cows and gas rate ?

40. Retention time
• Period of occupation of material inside digester
• RT = volume/ feed rate
• Generally RT > 20 days
• Wet AD process solid content of feed material < 10%
Biogas Generation – Design
Source RT
Cow dung 20
Poultry 25
Piggery 20
Market waste Continuous

41. Sizing
• Vd = SD x RT (m3)
• Total Volume = V1 + Vd + V2
• Vd = π HD2
• V1 = 0.09 D3
• V2 = 0.04D3
• R1 = 5D/7
• R2 = 1.06 D
• F1 = D/5
• F2 = D/8
Biogas Generation – Design

42. • Facilitate easy construction
• Easy operation and maintenance
• Safety
• Temperature (>35 C)
• Even surface, higher elevation for eliminate
water logging
• Sufficient distance from roots
• 10m distance from water bodies
Biogas Generation – Site selection

43. Suitable substrate
• Animal dung
• Human excreta
• Vegetable
• Food waste
• Organic effluents
• Mix of straw and dung
• Fruit waste
Biogas Unit – Operation

44. Favorable conditions
• C:Nratio around 25:1
• PH : 6-7
• Seed bacteria (floating BGM)
• No sudden changes of feed rate
• Isolation from free air
• Agitation
• Temperature (Soil temperature + 5 c)
Biogas Unit – Operation
Substrate C/N
Urine 0.8
Cattle dung 10-20
Piggery 9-13
Fresh grass 12
Excreta 8
Straw 40

45. Other consideration
• Shredding for fast reaction
• Effluent discharging (if not used as bio
fertilizer)
• Pressure measurement by manometer
Biogas Unit – Operation

46. Advantages of Biogas
• Waste treatment
– Reduce land fills
– Reduce soil & water pollution
• Energy Source
– Renewable
– Reduce GHG
• Bio fertilizer (Agriculture)
• Cheaper technology
• Job opportunities
Key disadvantages are : Little technology advancement, Not a clean gas
& unstable

47. Failures
17% of plants in Sri Lanka are not in
operation
• No responsible person
• No adequate biogas production
• Design failures
• Non availability of feeding material

48. Cost benefit calculation
• Assuming that , In a biogas plant when you
have an input of 100 kg of food waste the bio
gas yield will be approximately 30 meter cubic
per day.
• Methane presence of biogas is 70%
• Biogas calorific value: 37 MJ/m3
• LPG calorific value: 48 MJ/kg
• Investment: Rs. 650,000.00
• Calculate the cost benefit ?

49. would you install a biogas system?
?
BENEFITS TO MY INSTITUTE PROBLEMS TO OVERCOME

50. Thank You..!
• References
- NERDC Presentation, Sunil Karunawardane
- http://biofuellanka.com/biogas_plant.html