Biogas is normally produced by using the excreta of animals as the source material.
In most of the countries where biogas is produced, the excreta of the cattle and other farm animals are used. In India gobar or cow dung is used for the purpose of making biogas. 20% of the excreta of animals is made up of dust particles that are inorganic in nature. The percentage of the inorganic dust particles is brought down by combining water with the excreta in a 1:1 ratio. The rate of feeding of any biogas manufacturing plant that is based on dung is 3,500 kilograms per day.
Under normal circumstances the microbial content of the biogas is maintained by the addition of 2% of the expended slurry of the slurry of the fresh dung. 1% calcium ammonium nitrate of the dung is combined with the slurry in such cases. At times waste of kitchens and excrement of human bodies is used in these processes. The human excreta are supposed to occupy, at the most, 3% of the slurry.
The addition of human excreta is crucial in this context as it increases the amount of production of biogas. This is because human excreta have high nitrogen content. The ideal temperature for producing biogas is within 35 to 38 degrees Celsius. If the temperature is lower than that then the production of biogas may go down as well. If the temperature is 15 degree Celsius then it would be impossible to produce any biogas.
This is precisely the reason as to why thermal insulation is necessary to produce biogas when it is the winter season or at places where the temperatures are normally lower than the requisite level. The heating of digesters is also pretty important in this regard. The pH of the slurry has to be close to 7. This is pretty much possible provided that cow dung is employed in the form of a substrate. If favorable conditions may be provided then as much as sixty liters of biogas may be produced for one kilogram of cow dung.
The digesters that are used for the purpose of production of biogas can be used in mesophilic conditions, which mean a temperature range of 20 to 25 degrees Celsius to 40 to 45 degrees Celsius. The digesters can also be run in thermophilic conditions, where the temperature range is from 50 to 55 degrees Celsius to 60 to 65 degrees Celsius.
Both these conditions call for separate species of bacteria. It is thought that the mesophilic operations are more safe and stable than the thermophilic operations that are capable of inactivating the parasites of animals and the various pathogens.
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Professor of Economics & Director of the Earth Institute at Columbia University. Special Adviser to the UN Secretary-General on the Millennium Development Goals. Founder & co-President of the Millennium Promise Alliance.
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