• Plant matter created by process of photosynthesis is called biomass. It includes all plant life, trees, agricultural plants, bush, grass, algae and livestock wastes.
  • Photosynthesis is a naturally occurring process which derives its energy requirement from solar radiation. In its simplest form the reaction of this process can be represented by H2O + CO2 à CH2O+O2.
  • It is seen that in this process, water and carbon dioxide are converted into organic material. The gas produced by biomass is called biogas.
  • Biogas is obtained through the fermentation of animal waste and other biomass in a digestion chamber. Biogas is a mixture of methane (45 to 70 per cent) and carbon dioxide.
  • The production of biogas is of particular significance for India because of its large cattle population.

History of Biogas

  • History of biogas in India is petty old. Sri.S.V.Desai of Indian Agricultural Research Institute, New Delhi was a pioneer man in India who worked extensively on this subject in 1937. After that, contribution of Prof.N.V.Joshi of I.A.R.I. in 1964 is of great significance, Sri Satish Chandra Das Gupta had studied in detail the different aspects of biogas in the year 1952. Besides these, a large number of persons worked on different aspects of biogas at different places. Khadi and Village Industries Commission (KVIC) started a project on biogas in a big way in 1962.

Biogas Plant

  • It is a composite unit consisting of : (1) Digester and (2) Gas holder. The gas holder floats on the top of digester in conventional designs (Fig.2.1.). In KVIC design the gas holder is a fixed type unit.


  • It is a chamber containing the animal waste in the form of slum. It is normally situated below the ground level. It is made of masonry work.
  • There is a partition wall in the middle of the digester which divides the digester into semi-circular compartments.
  • Two slanting pipes are fitted to reach the bottom of the well on either side of the partition wall. There is one inlet pipe and another outlet pipe for the system. Outlet opening is lower than the inlet opening.
  • The diameter of the digester ranges from 1.2 to 6 metres while its depth ranges from 3 to 6 meters.

Gas Holder

  • It is a drum like structure of mild steel sheet in conventional designs. It is like a cap on the mouth of the digester where it dips in the slurry and rests on suitable base inside the digester.
  • Gas holders may be made of mild steel sheet, fibre glass, reinforced plastic (RFP) and high density polythelene (HDP). In some designs there is fixed type gas holder.

Gas generation process

  • The gas generation process occurs in two stages. In the first stage the organic substance contained in the waste are acted upon by certain kind of bacteria called acid formers.
  • The material is broken up into small chain simple acids. On the second stage, these acids are acted upon by another kind of bacteria which produce methane and carbon dioxide. The biogas contains about 55% methane (CH4) and about 45% carbon dioxide (CO2).

Feeding process of slurry

  • Cattle dung is mixed with water in the proportion of about 4:5 ratio and fed through inlet opening. Cattle dung can be obtained from buffaloes, bullocks, cows and calves.
  • Buffaloes give about 15kg dung per day, bullocks or cows give about 10kg dung per day and calves give about 5kg dung per day.

Gas Plant Capacity

  • Gas plants are available in nearly 20 sizes ranging from 2 to 150 cubic metre. Smallest plant may be 2 cubic meter size where 2 to 3 animals are required.
  • Gas production may be 0.037m3 per kg of wet dung.
  • For cooking purpose 0.227 m3 gas per day per person may be required.
  • For lighting purpose 0.127 m3 gas per lamp of 100 candle power may be required.
  • For a 5 hp engine, 18 m3 gas may be required for 8 hours.

Condition for gas production

  • Suitable condition for gas production is when the pH of the slurry is between 7 to 8 in the digestion chamber. Bacteria dies when the pH is above 8 in the digestion chamber.
  • Gas production is at higher rate when the temperature inside the chamber is around 35°C. The process is retarded very much below 15°C.


  • Gas is used for : (i) cooking purpose (ii) lighting (iii) running of diesel engine (iv) fertilizer supply. The sludge which comes out from the gas plant retains all the nitrogen, phosphorus and potassium, so it is an excellent fertilizer at the farms.
Last modified: Thursday, 10 May 2012, 7:28 AM