2. Biogas originates from biogenic material and is a type of biofuel.

3. One type of biogas is produced by anaerobic digestion or fermentation of biodegradable materials such as biomass, manure, sewage, municipal waste, green waste and energy crops.

4. This type of biogas comprises primarily methane and carbon dioxide.

5. The other principal type of biogas is wood gas which is created by gasification of wood or other biomass.

7. Different problems are encountered with each of these wastes with regard to collection, transportation, processing, storage, residue utilization, and ultimate use.

8. Industrial and food processing waste:these arise from sugar, potato, vegetable and fruit processing, brewery and distillery wastes, and whey from cheese production.

9. Animal excreta and agricultural wastes:these are solid wastes rich on cellulose and lignocelluloses.

10. Agricultural biomass like straw, bagasse, etc. show poor digestibility and often high C : N ratio.

12. They remove the small amounts of O2 present and create anaerobic conditions.

13. These bacteria hydrolyze and ferment the organic materials, e.g., cellulose, starch, proteins, sugars, lipids etc., and produce organic acids, CO2 and H2.

14. Syntrophic H2 producing bacteria:these bacteria break down organic acids having greater than 2 carbon atoms in their chain to produce acetate, CO2 and H2.

15. Methanogenic bacteria:this group of bacteria converts acetate, and CO2 + H2 into methane.

16. Thus methanogens remove the H2 produced by obligate H2 producing bacteria, thereby lowering the H2 partial pressure and enabling the latter to continue producing H2.

17. Methanogenic bacteria are the strictest possible anaerobes known.

18. They may occur up to 106-108 cells/ml of the slurry in digesters.

19. e.g., Methanosarcina barkeri, Methanobacterium omelianskii.

20. Acetogenic bacteria:these bacteria oxidize H2 by reducing CO2 to acetic acid, which is then used up by methanogens to generate methane, CO2 and H2.

22. Recovery of the product is spontaneous

23. Aseptic conditions are not needed for operation.

24. Any biodegradable matter can be used as substrate.

26. The process is not very attractive economically on large industrial scale.

27. The biogas yields are lower due to the dilute nature of substrates used.

29. India is one of the pioneer countries in biogas technology where biogas research and plant construction has been carried out over the past 30 years.

30. In 1951, for the first time, biogas plants were constructed with the target of 8,000 units before 1973.

31. Government of India launched an all India coordinated project with the target of 1,00,00 units by 1978, but the number could reach to 50,000 units only.

32. Up to 1993, non-conventional energy development agency (NEDA) of Uttar Pradesh has installed about 100 night soil based biogas plant throughout the state.

33. The sewage plant at Okhla has 15 digesters of 5665 m3 capacity each and produces 17,000m3 gas per day.

34. The gas generated is equivalent to about 10,000 liters of kerosene per day, where 1 m3 biogas has energy potential equal to about 2/3 liters of kerosene.

35. The Dadar sewage treatment plant produces about 2800 m2 biogas per day from sewage.

36. In Sonepat district of Haryana, over 300 biogas units of 2 to 10 m3 capacity have been set up for cooking and lighting purposes.

37. The Haryana government provided 25% subsidy per plant for setting up the units.

38. Himachal Pradesh government set up the National Project on biogas, under which about 12, 292 units in 1987-89 and 3,505 units in 1989-90 were setup.

39. National sugar institute (Kanpur) has developed methods for production of biogas from bagasse and other agricultural residues.

40. This plant was built up in 1960s.

41. In this plant, 12 steel digesters, each having capacity of 50 m3, are set up to which about 14 tones of mixture of agricultural wastes and cattle manure and 28 tones of water are fed to begin the biogas production.

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