This document discusses biogas production through anaerobic digestion. It describes the key components of a biogas plant including the digester, gas holder, inlet, and outlet. The four step process of biogas production is outlined as hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Major genera of methanogenic bacteria that create methane are discussed. Factors that influence methane formation like pH, temperature, nitrogen concentration, and carbon to nitrogen ratio are also summarized.

1. KASHMEERA N.A.
IV SEM MSc ZOOLOGY
ROLL No: 37
03/13/13

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4. Mystery unveiled….
Alessandro volta
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5. BIOGAS
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Mixture of gases.
•
Produced by anaerobic digestion of organic
matter.
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Consist of CH4 ,CO2 ,traces of H2 & other gases.
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6. Composition of Biogas
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8. BENEFITS FROM BIOGAS PLANTS
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Used mainly for cooking & lighting purposes.
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Used in internal combustion engines to power
water pumps & electric generators.
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Used as fuel in fuel type refridgerators.
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Sludge - fertilizer.
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↓ envt. pollution
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11. SUBSTRATE
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Plant & animal biomass.
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Plant biomass –
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Animal biomass – cattle dung,manure from
poultry,goats & sheep slaughter house &
fishery wastes.
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Agricultural wastes also used
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13. Parts of biogas plant
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Digester
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Gas holder
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Inlet
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Outlet
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14. Inlet chamber
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To supply cow dung to the digester
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It is made at the ground level so that the cow dung
can be poured easily.
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made up of bricks, cement and sand.
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The outlet wall of the inlet chamber is made inclined
so that the cow dung easily flows to the digester.
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15. Digester
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Most important part of biogas plant
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Fermentation takes place - fermentation tank.
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Built underground – insulated,airtight
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Made up of bricks, sand and cement.
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16. •
Almost at the middle of the height of
digester, two openings are provided on the
opposite sides for inflow of fresh cow dung
and outflow of used cow dung.
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17. Gas holder
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Cylindrical container
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Above digester
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Collect gas
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The gas pipe carries the biogas to the place
where it is consumed.
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18. Outlet Chamber
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Digested slurry from which the biogas has
been generated is removed from the biogas
plant.
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The outlet chamber is also at the ground level.
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20. Types
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GAS HOLDER
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Fixed dome type
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Floating drum type
FREQUENCY OF FILLING
SUBSTRATE
Batch type
Continuous type
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21. Fixed dome type
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A fixed-dome plant consists of a digester with
a fixed, non-movable gas holder, which sits on
top of the digester.
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22. Floating-drum type
•
Consist of an underground digester and a
moving gas-holder.
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Gas-holder floats either directly on the
fermentation slurry or in a separate water
jacket.
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The gas is collected in the gas drum, which
rises or moves down, according to the amount
of gas stored
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23. Floating-drum type
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24. •
Batch type
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Filled once,sealed.
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Emptied when raw materials stop producing
gas.
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Continuous type
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Fed with a definite quantity of wastes at
regular intervals
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Gas production continuous & regular
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26. MICROBIOLOGY OF BIOGAS
•4 steps
•Hydrolysis
•Acidogenesis
•Acetogenesis
•Methanogenesis
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27. Hydrolysis
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Biomass is made up of large organic polymers
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Complex polymers hydrolysed to monomers
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complex organic molecules → simple sugars, amino
acids, and fatty acids.
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Done by hydrolytic fermentative bacteria
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28. Acidogenesis
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Results in further breakdown of the remaining
components by acidogenic bacteria.
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Ammonia, H2, CO2, H2S, shorter volatile fatty acids,
carbonic acids, alcohols, as well as trace amounts of
other byproducts produced
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29. Acetogenesis
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Simple molecules created through the
acidogenesis phase further digested to acetic
acid, carbon dioxide and hydrogen.
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Acetogenic bacteria
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30. Methanogenesis
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The terminal stage
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Intermediate products of the preceding stages
converted to methane, carbon dioxide, and
water.
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These components make up the majority of
the biogas emitted from the system.
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Methanogenic bacteria
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31. MICRO ORGANISMS
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Hydrolytic & fermentative bacteria.
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Acidogenic bacteria.
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Acetogenic bacteria.
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Methanogenic bacteria.
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33. Methanogenic bacteria.
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Create methane from the final products of
acetogenesis as well as from some of the
intermediate products from hydrolysis and
acidogenesis .
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Archaebacteria
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34. MAJOR GENERA OF METHANOGENIC BACTERIA
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35. •
Cocci
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Spirilli
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Bacilli
Cocci forming colonies
in cubical packets of
•
sarcina eight or more are called
sarcina
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36. •
Methanogens are a diverse group of organisms that
can live in a wide range of environments.
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They have been found in a range of salinity from
freshwater to hypersaline.
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37. •
Biogas plant – Methanosarcina barkeri,
Methanobacterium omelianskii
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39. Factors affecting methane formation.
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pH
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Temperature
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Nitrogen concentration
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C:N ratio
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Creation of anaerobic conditions
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40. pH
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6-8
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Acidic medium lowers methane formation.
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Temperature
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Fluctuation ↓ methane formation – inhibit
growth of methanogens.
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30-40oC
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41. Nitrogen concentration
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↑ N2 - ↓ growth of bacteria - ↓ CH4
C:N ratio
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Micro organisms in a biogas plant needs both N
nitrogen and C carbon.
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Research has shown that the methanogenic bacteria
work best with a C/N ratio 30:1.
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42. Creation of anaerobic conditions
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CH4 production takeplace in strictly anaerobic
condition.
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Digesters – airtight, burried under soil.
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