What is biogas?
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  • Date:2011/1/21

What is biogas?

Biogas is a combustible mixture of gases produced by micro-organisms when livestock manure and other biological wastes are allowed to ferment in the absence of air in closed containers. The major constituents of biogas are methane (CH4, 60 percent or more by volume) and carbon dioxide (CO2, about 35 percent); but small amounts of water vapour, hydrogen sulphide (H2S), carbon monoxide (CO), and nitrogen (N2) are also present. The composition of biogas varies according to the biological material. The methane content of biogas produced from night soil (human excreta), chicken manure and wastewater from slaughterhouse sometimes could reach 70 percent or more, while that from stalk and straw of crops is about 55 percent. The concentration of H2S in biogas produced from chicken manure and molasses could be as high as 4 000mg/m3, and from alcohol wastewater even higher at 10 000 mg/m3. Biogas is mainly used as fuel, like natural gas, while the digested mixture of liquids and solids ‘bio-slurry’ and ‘bio-sludge’ are mainly used as organic fertilizers for crops. But there are numerous other uses for biogas, bio-slurry and bio-sludge in China.

What is the advantage of the biogas?

 The advantages of biogas are manifold. Biogas by itself can positively affect the economy of rural areas. The principal benefits of biogas include: Conversion of natural organic waste into fertilizer: The conversion is carried out in a machine called the polythene bio gas digester. Cow dung slurry is put into the machine. The product is organic fertilizer of high quality. The fertilizer obtained is rich in nitrogen.

It has been analyzed, that, fertilizer made by the polythene bio gas digester contains nitrogen content 3 times more than the product made by conventional processes. It is completely natural and free from harmful synthetic chemicals.

Eco friendly energy production: The calorific value of biogas is equal to that of half liter of diesel oil (6 kWh/m3). Methane is a key component of the gas. Biogas is fully capable of replacing other rural energy sources like wood, hard coal, kerosene, plant residues, and propane. Hard coal possesses a calorific value of 8.5kWh/kg per 0.7 kilograms. Larger biogas plants generate and feed electricity into mainstream power grids. Smaller biogas production units can support lighting and cooking requirements

Considerable workload reduction in rural areas: This is particularly true for rural women engaged in day to day household work. Installing a biogas unit will relieve her of the tiring and tedious job of collecting and ferrying firewood. Since, biogas burns cleanly, the rural homes will not suffer from smoke and consequently rural denizens will suffer less from physical problems like bronchial complications. Cooking is also easier with a gas stove and takes less time.

Visible improvement in rural hygiene: Biogas contributes positively to rural health conditions. Biogas plants lower the incidence of respiratory diseases. Diseases like asthma, lung problems, and eye infections have considerably decreased in the same area when compared to the pre-biogas plant times. Biogas plants also kill pathogens like cholera, dysentery, typhoid, and paratyphoid.

Environmental benefits on a global scale: Biogas plants significantly lower the greenhouse effects on the earth's atmosphere. The plants lower methane emissions by entrapping the harmful gas and using it as fuel
Protects the earth's natural resources: 1 biogas plant is computed to save 32 liters of kerosene and 4 tons of firewood every year. The organic chemical plant. also contributes indirectly to the protection of soil.

Is the biogas same sa natural gas?

No. Natural gas was formed 150 million years ago in pockets of the earth crust and in porous rock. It is a non-renewable, fossil fuel recovered from deep gas wells. Biogas is the product of the natural biological breakdown of crop and animal waste when the supply of oxygen is restricted. This is a continuous, ongoing process in Nature and it also takes place under controlled conditions in our sewage plants and landfills.

Natural gas and biogas both contain methane. If biogas is refined, with everything except methane being removed, its properties are then similar to those of natural gas. This means that the technology that has been developed for the distribution and use of natural gas can also be used for biogas.

What can biogas be used for?

Biogas is energy rich and is well suited as a source of energy within many areas. 

Biogas for heating

Perhaps the easiest way to use biogas is for heating. This is because, for this purpose, no pre-treatment other than the removal of water is required. Biogas is usually used for heating buildings in conjunction with a biogas plant, but surplus heat can also be directed into the district heating network.

Biogas power generation

Biogas energy can also be used to generate power. Both electricity and heat can be produced with the help of a gas powered generator. The proportions of heat and power generated depend of course on the design of the plant but are usually in the region of 35 per cent electricity and 65 per cent heat.

Biogas as vehicle fuel

Relatively speaking, biogas requires considerable processing if it is to be used as vehicle fuel. The energy value has to be raised by separating carbon dioxide in order to achieve a methane content of between 95 and 99 per cent. Water, impurities and particles must be removed to avoid mechanical as well as environmental damage. Finally, the gas has to be compressed. Although significant work is needed to upgrade methane gas to biogas fuel, the environmental benefits are so great that an increasing number of filling stations are opening throughout the country.

Biogas in industry

Many industries such as sugar refineries, distilleries, dairies and paper mills generate processing and waste water that can be digested directly on site. Biogas can thus be used for heating premises, district heating power production, heating ovens etc.

Where do biogas come from?

Biogas develops in a completely natural process that takes place anywhere that organic waste is produced. During the process, the waste is broken down by microorganisms, resulting in a nutritious, energy rich end product.


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