Biogas is a gaseous mixture of varied composition, generally composed of about 65 cent methane (a high value fuel), 30 per cent carbon dioxide (inert gas) and traces of other gai it is produced from anaerobic fermentation (in absence of air) of organic waste.
Contents of Biogas:
Methane = 65 per cent
Carbon dioxide = 30 per cent
Hydrogen = 4 per cent
Sulphur dioxide = 1 per cent
It has a calorific value of more than 5,000 KCal/m3 depending on its carbon dioxide content Wastes, which can be used for production at various levels, are:
(i) Village, farm level: Agricultural wastes/vegetable wastes
(ii) Household units: Animal wastes/domestic garbage
(iii) Large city level: Municipal garbage/sewage
(iv) Industrial level: Industrial effluents/solid wastes of dairy, distillery, brewery, f<xn processing units, canning, chemical industries etc.
Anaerobic digestion of biogas production involves activity of three groups of organism
(i) Solubilisation and Hydrolysis of organic components: Fermentative bacteria convert complex organic material into organic acids, alcohols, esters, sugars, and COr
(ii) Acidogensis: The group is dependent on the first and contains hydrogen and acid producing bacteria.
(iii) Methanogenesis: Methanogenic bacteria convert acetate and H, into biogas, which is a mixture of Methane (CH4) and CO.
The gas consumption for different uses is as follows:
1. For cooking 8 cuft per day.
2. For lighting 4-5 cuft per 100 candle power/lamp/hour and
3. For motive power 15 cuft per horsepower.
Formation of Methane from whey components
Biogas production from wastes is given more and more importance because it couples degradation of wastes to energy production and not energy consumption. Reactors of various designs and sizes ranging from 2000-20,000 m3 capacities are in use and loads of 25.30 kg COD m"3d'' are handled.
In India, successful experiments have been done for developing gobar gas. Biogas is an important solution to present energy crisis, especially in rural areas. In India, biogas production already has reached an equivalent of 35 lakhs tonnes of fuel wood.
1. This is an environmentally clean technology. In the fermentation process many pathogens get destroyed as well and this could reduce health hazards.
2. Reduction in the incidence of eye disease among women and easy and efficient cooking and thereby reducing the drudgery in women's life.
3. There is plenty of animal dung every year, from which about 22,425 million m3 gases can be produced. In biogas technology, the important factors are dung excrement and availability, gas yield, calorific value and appliance efficiency.
4. Its other benefits include improvement in sanitation.
1. In order to make best use of biogas technology, two things are relevant: restricted use of water and better strains of methane generating bacteria. For normal microbal activity 90 per cent water content is needed, whereas in bovine manure and human waste, this value is 80 per cent. Thus we need additional water, which may be critical to this technology in drier areas of the country.
2. Land area is also a factor.
3. The ideal temperature for methane generation is 35°C or more. In Northern areas, production stops at 10°C.
Biogas can also be generated from sludge obtained from primary treatment of raw sewage and one such plant is in operation at Okhla, Delhi. There have been developed Urja Grams by using biomass, animal, poultry waste and human excreta.