biogas

Biogas (Gobar gas) Plant 

 Biogas plant is a system comprising of a gas-holder and a

digestion chamber, in which “Gobar” (or cow dung) can be

treated anaero bically to produce two important and useful items

viz., fuel gas (or biogas) and organic manure. In this biochemical

process the cellulotic material are broken down to methane and

carbon-di-oxide by different groups of microorganisms. It is a

clean, unpolluted and cheap source of energy, which can be

obtained by a simple mechanism and little investment. India was

the first country in the world to have developed a biogas plant on

an experimental basis as early as 1939, followed by the

installation of a commercial model in 1954. Later, the Khadi and

Village Industries Commission (KVIC) adopted the biogas

programme in 1962, and was instrumental for intiating biogas

plants in India.

Types of biogas plant: 

1. Float dome type: Different models are available in this

category, e.g., KVIC vertical and horizontal, Pragathi

model & Ganesh Model.

2. Fixed dome type: The gas plant is dome shaped under

ground construction. The entire construction is made of

bricks and cement. The models available in this category

are Janata and Deen-Bandhu.

The selection of a particular type depends on technical,

climatological, geographical and economic factors.

Technical information 

• Biogas is compsed mainly of methane (55 – 60%) and

Carbon Dioxide (35 – 45%). Hydrogen and hydrogen

sulphide can also be present in small amounts. 

• Availability of fresh dung per stable bound medium sized

animal per day is a follows: buffalo - 15kg; Cow – 10kg;

and Calves – 5kg.    

• Recommended size of biogas plant according to cow dung

availability is shown in Table 13.3

Table 13.3. Size of biogas plant

Gas

production

(size) in M

3

Fresh cow dung

required/day

No. of

animals

required

2 50 4 -5

3 75 6 – 8

4 100 9 – 11

6 150 14 -16

8 200 18 -22

10 250 24 -28

• The NPK content of the residual sludge in the dry state is

equivalent of N = 1.4 - 1.8% ; P

2

O

5

 = 1.1 – 2.0% ; K

O =

0.8 – 1.2% 

• From each kilogram of fresh dung charged in to the

digester every day, gas production will be about 0.04 – 0.1

m

3

 depending upon the day temperature. Gas production

would be maximum at a temperature between 30-35

C. If

the ambient temperature falls below 10

o

C, gas production

is reduced drastically. 

• One m

3

 of biogas is equivalent to 0.62 litres of kerosene

• A 2 m3 biogas plant would cater to domestic needs of a

family of 6 – 8 members

Site selection and management: The site of biogas plant

should be close to the kitchen and cattle shed to cut down the

cost on gas distribution system and transportation of cattle

dung Land should be leveled and slightly above the ground

level to avoid inflow or run-off of water. Plant should get

clear Sunshine during most part of the day. Gas generation is

a function of dung availability. The amount of gas production

is considerably higher in summer followed by rainy and

winter seasons.

Uses of biogas: It can be efficiently used for domestic

cooking and lighting. It can also be a used as a substitute fuel

for running diesel engine. It does not emit smoke and also

does not soot on the vessels unlike other conventional forms

of fuel viz., coal, fire-wood and kerosene. 

o

2

Uses of bio-gas slurry: Slurry is obtained after the

production of bio-gas. It is enriched manure containing NPK

and humus. Another positive aspect of this manure is that

even after weeks of exposure to the atmosphere, the slurry

does not attract fleas and worms.