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PinkMonkey Online Study Guide-Biology

9.4 Methane

As stated earlier in this chapter, the common raw materials used for the production of methane are biomass products such as human and animal wastes, agricultural, industrial and domestic residues. Cattle dung is the most common material used in most biogas plants.



Process involved

Group of bacteria involved



Hydrolytic fermentor bacteria

(mostly anaerobic).



Hydrogen - producing acetogenic

bacteria (facultative anaerobic)



Methanogens( i.e. methane

producing anaerobic bacteria)

Micro-organisms involved : Conversion of the biomass into biogas (methane) is a process called anaerobic digestion. It is completed in three stages. Breakdown of the biomass as each stage is done by a different group of bacteria as shown in the above table.

Gobar gas plant (Figure 9.2) : As the biogas (gobar gas) production is an anaerobic process, it is carried out in an air tight, closed cylindrical concrete tank called a digester. In countries like India, domestic gobar gas plants use single digester tanks (Fig. 9.2). The tank has a concrete inlet basin on one side for feeding fresh cattle dung (gobar). There is a concrete outlet on the outer side for removing the digested sludge. The top of the tank serves as the gas tank. It has an outlet pipe for the gobar gas/ biogas.

Figure 9.2 Domestic Gobar gas plant (Diagrammatic)

Process : Fresh cattle dung is fed into the digester tank through the inlet and allowed to remain there. After about 50 days, a sufficient amount of gobar gas is accumulated in the gas tank. It is conducted through the outlet pipe and used for domestic purposes. The digested sludge (digested biomass) is removed from the tank and is used as fertilizer. The tank is again filled with fresh dung and the process is repeated.


(1) Gobar gas is mainly used for cooking and lighting in rural areas.

(2) Also used in internal combustion engines to power water pumps and electric generators.

(3) Used as a fuel in the fuel type refrigerators.

There are certain advantages in using methane (gobar gas) as a source of energy :

i. Methane is very insoluble, hence it separates very readily from the fermentor system.

ii. It can be very easily collected, pressurized or liquified for storage.

iii. It is readily combustible.

Other advantages are :

(a) Sludge is used as fertilizer.

(b) It serves as a pollution free method for the disposal of human and animal wastes in rural areas.

(c) The anaerobic process involved also eliminates pathogenic bacteria from the biomass.

Table of Contents

9.0 - Introduction
9.1 Common Methods of Biogas Formation
9.2 Raw Materials and Substrates
9.3 Producer Gas
9.4 Methane
9.5 Plants as Sources of Hydrocarbons

Chapter 10


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