Biogas is a mixture of 55-65% Methane, 30-35% Carbon Dioxide and Moisture, Hydrogen Sulphide, Nitrogen and Hydrogen making up the balance.
Its heating value is around 600 B.T.U. per cubic feet. Biogas production is a biological process without oxygen in which organic matters are converted into biogas by bacteria, because organic matters are the food source for methane producing bacteria. About one cubic feet of biogas may be generated from one pound of cow dung at around 28°C.
This is enough to cook a day's meals for 4-6 people. In anaerobic process, the bacteria requires both Carbon and Nitrogen, but they consume Carbon roughly 30 times faster than Nitrogen. Biogas is not poisonous, although this may be improved by filtering it through limewater to remove CO2, iron filings to absorb corrosive H2S and Ca2Cl to extract the water vapour. The only danger is by the explosion of the plant and mixed with air and fire. Thus proper maintenance of the Biogas plant is important to prevent the leakage.
Benefits of biogas
Biogas systems make clean energy for household use as fuel for lighting and cooking and to operate the gas engine. This system is an advantage for rural economic development and to prevent the deforestation and also to protect the earth from global warming.
The biogas process produces a moist rest product (Biorest) at the outlet of the Biogas plant. The Biorest contains 1.8-2.4% of ammonia, 0.6-0.8% of potassium and 1.0-1.2% of phosphorus, 50-75% of stable organic matter and biomass.
The fermentation of manure in the biogas production greatly reduces the pathogen content in livestock manure. It can be used as a fertilizer in the crop cultivation.
Lay out of the Mini Biogas Plant for Household Use
The following biotic and abiotic factors are required for biogas production.
1. Organic matters
3. Anaerobic condition
Biogas process is the last choice of the bacteria after the oxidation and acidic and alcoholic fermentation. Organic manure is fed into the digester via inlet pipe and undergoes digestion in the digestion chamber.
Anaerobic breakdown of waste occurs at temperatures lying between 0°C and 69°C but the action of the digesting bacteria will decrease sharply below 16°C. Researchers revealed that temperature between 32°C and 35°C and within a pH range of 6.8 to 8.0 have proven most efficient for stable and continuous production of methane. Shaking the slurry in a digester is always advantageous. If not stirred, the slurry will tend to settle out and form a hard scum on the surface which will prevent release of the biogas. This problem is much greater with vegetable waste than with manure. Biogas production can be greatly increased by adding certain types of food waste, corn silage with the cattle manure.
The first type of bacteria converts the fats, carbohydrates and proteins present in the organic matters to simple acids such as acetic acid, propionic acid. Then the second type of bacteria transforms the acids to methane and carbon dioxide. The biogas process produces no waste products.