•Composition of biogas
•Advantages and disadvantages
•Biochemical reaction and stages of anaerobic digestion
•Modes of operation
•Types of anaerobic digesters
What is biogas?
Biogas is a methane rich flammable gas that results from the
decomposition of organic waste material
Biogas is produced by anaerobic digestion or fermentation of
biodegradable materials such as biomass, manure, sewage,
municipal waste, green waste, plant material and energy crops.
Biogas also called as ‘Marsh gas’
Biogas is a type of biofuel.
This type of biogas comprises primarily methane and carbon
Composition of biogas
Biogas is generated by the activity of anaerobic bacteria
Composition depends on: the composition of raw material,
organic loading to digesters, time and temperature of
Composition of biogas
50 - 70
30 - 40
5 - 10
1 - 2
Advantages of biogas
• Production of large amount of methane gas (ambient
• Production of free flowing thick sludge
• Odourless sludge
• Sludge can be used as fertilizer and soil conditioner
• Sanitary way for human and animal waste disposal
• Conservation of scarce resources like wood
High capital lost
Incorrect handling of liquid sludge causes pollution
Requires control and maintenance
Needs proper condition
• Use as a fuel requires removal of CO2 and H2S
Factors affecting yield and production of
Many factors affecting the fermentation process of
organic substances under anaerobic condition are,
The quantity and nature of organic matter
Acidity and alkanity (PH value) of substrate
The flow and dilution of material
CH4 + CO2 + H2 + NH3 + H2S
Stages of anaerobic digestion:
1.Liquefaction by hydrolytic enzymes
3.Methane formation with methanogen production
Liquefaction by hydrolytic enzymes
• Complex organic matter is degraded to basic structure
by hydraulic bacteria.
Protein - Polypeptide and Amino Acid
-Glycerin and Fatty Acid
Amylose - Monosacride and Polysacride
• Also called the acidogenesis
• Simple organic matters are converted into acetic acid, H2
• Acting bacteria in this process are called hydrogenproducing bacteria and acid-producing bacteria.
• In this process, acetic acid, H2, CO2, are converted into CH4.
• Methane-producing bacteria have strict PH requirement and
low adaptability to temperature.
• Methanococcus jannaschii, Methanobacterium thermoautotrophicum
Modes of operation
• Semi-continuous – regular feeding of digester and
decrease of organic matter at intervals
• Continuous – for liquid waste treatment
• Suited for large-scale manure substrate bioreactor.
• Steady biogas production can be expected.
• May require auxiliary equipments.
• Requires high liquid content.
• Temperature, loading rate, and solid content need to be
The simplest design.
The feedstock is loaded one batch at time.
Irregular biogas production.
Can operate on high solid content.
Requires manual labor.
Types of digesters
A typical biogas system consists of the following components:
(1) Manure collection
(2) Anaerobic digester
(3) Effluent storage
(4) Gas handling
(5) Gas use.
TWO MAIN TYPES:
1. Digesters utilizing dispersed growth of bacteria
2. Digesters utilizing attached growth of bacteria
DISPERSED GROWTH DIGESTERS
Fixed dome digester
Floating gas holder digester (Indian)
Plug flow digester (horizontal displacement)
Bag digester (Taiwan and Korea)
Separate gas holder digester
Fixed dome digester
with a dome on the top
for gas storage.
The fermentation chamber and gas holder are combined as one unit.
Eliminates the use of costlier mild steel gas holder which is
susceptible to corrosion.
20 to 50 years.
Floating gas holder digester
Jashu Bhai J Patel developed a
design of floating drum biogas
Popularly known as Gobar Gas
In this design, the digester chamber is made of brick masonry in cement
A mild steel drum is placed on top of the digester to collect the biogas
produced from the digester. Thus, there are two separate structures for
gas production and collection.
• It consists of a long cylinder made of PVC or red mud plastic.
• The bag digester was developed to solve the problems experienced
with brick and metal digesters.
It consists of a column
filled with a packing
A great variety of nonbiodegradable materials
have been used as
anaerobic filter reactors
such as stones, plastic,
coral, mussel shells,
reeds, and bamboo rings.
The methane forming bacteria form a film on the large surface of the packing
medium and are not carried out of the digester with the effluent.
For this reason, these reactors are also known as "fixed film" or "retained film"
The UASB reactors contain no packing medium, instead, the
methane forming bacteria are concentrated in the dense granules of
sludge blanket which covers the lower part of the reactor.
The feed liquid enters from the bottom of the reactor and biogas is
produced while liquid flows up through the sludge blanket.
Gas Production potential of various types of dung
Types of Dung
Gas Production Per Kg Dung
Cattle (cows and buffaloes)
0.023 - 0.040
0.040 - 0.059
0.065 - 0.116
0.020 - 0.028
Material and methods
• The Sewage Treatment Plant has capacity to treat 18 mld sewage
from main pumping station.
• After primary and secondary treatment, sludge is remain left that
is being collected in thickener.
• Around 96X105 liters sludge is being drained from thickener to
digester tank at each 12 hrs.
• The sludge was taken from thickener and digester tank and
Temperature, pH, Total solids %, Volatile solids %, and Alkalinity
parameters were analyzed
The present study was done in the months of winter and
summer and the sampling were done seasonally from the
sewage treatment plant.
Raw sewage consists of organic and inorganic solids in
dissolved and suspended form with 90-99.9% of water
Materials and methods
In this study, experiments were conducted to investigate the production of
biogas from municipal solid waste (MSW) and domestic sewage by using
anaerobic digestion process.
The MSW is collected from the Perungudi yard at the Chennai metropolitan
city. The yard has an area of approximately 10 km2.
Domestic sewage is collected from a college campus before disposal to the
treatment plant. It is used in all digestion experiments for diluting the feedstock
to achieve the required total concentration of TS.
The domestic sewage is added to MSW, which is in the form of dry and
shredded waste. Here both the wastes are mixed so that it forms slurry.
• The digester was operated at different organic feeding rates of 0.5, 1.0,
2.3, 2.9, 3.5 and 4.3 kg of volatile solids (VS)/m3 of digester slurry per
• Biogas generation was enhanced by the addition of domestic sewage to
• The maximum biogas production of 0.36m3/kg of VS added per day
occurred at the optimum organic feeding rate of 2.9 kg of VS/m3/day.
Henry, C., 2006." What is an Anaerobic biodigester?”
http://www.fao.org.in (Biogas technology: a training manual
for extension" (FAO/CMS, 1996)
Polprasert, C., 1989. Biogas production. In: Organic waste
recycling. John Wiley Sons. Ltd., Great Britain. 105-144