Friday, April 3, 2009


What is biogas?

Biogas originates from bacteria in the process of bio-degradation of organic material under anaerobic (without air) conditions. In the absence of oxygen, anaerobic bacteria decompose organic matter and produce a gas mainly composed of methane (60%) and carbon dioxide called biogas. This gas can be compared to natural gas which is 99% methane.

Biogas and the global carbon cycle

Each year some 590-880 million tons of methane are released worldwide into the atmosphere through microbial activity. About 90% of the emitted methane derives from biogenic sources, i.e. from the decomposition of biomass. The remainder is of fossil origin (e.g. petrochemical processes). In the northern hemisphere, the present troposphere methane concentration amounts to about 1.65 ppm(parts per million).

Unlike fossil fuel combustion, biogas production from biomass is considered CO2 neutral and therefore does not emit additional Greenhouse Gases (GHG) into the atmosphere.

However, if biogas is not recovered properly, it will contribute to a GHG effect 20 times worst than if methane is simply combusted. Therefore, there is a real incentive to transfer biogas combustion energy into heat and/or electricity.

Finally, biogas production from anaerobic digester presents the additional advantage of treating organic waste and reducing the environmental impact of these wastes. It contributes to a better image of the farming community while reducing odor, pathogens and weeds from the manure and producing an enhance fertilizer easily assimilated by plants.

Benefits of Biogas

A Biogas unit can yield a whole range of benefits for their users, the society and the environment in general, the chief benefits being;

1. Production of energy (heat, light, electricity).

2. Transformation of organic wastes into high quality fertilizer.

3. Improvement of hygienic conditions through reduction of pathogens, worm eggs and flies.

4. Reduction of workload, mainly for women, in firewood collection and cooking.

5. Environmental advantages through protection of forests, soil, water and air.

6. Global Environmental Benefits of Biogas Technology.

1. Production of energy (heat, light, electricity)

The calorific value of biogas is about 6 kWh/m3 - this corresponds to about half a litre of diesel oil. The net calorific value depends on the efficiency of the burners or appliances. Methane is the valuable component under the aspect of using biogas as a fuel.

Biogas use, replacing conventional fuels like kerosene or firewood, allows for the conservation of environment. It therefore, increases its own value by the value of i.e. forest saved or planted.

Biogas is able to substitute almost the complete consumption of firewood in rural households.

1 m3 Biogas (approximately 6 kWh/m3) is equivalent to:

  • Diesel, Kerosene (approx. 12 kWh/kg) 0.5 kg
  • Wood (approx. 4.5 kWh/kg) 1.3 kg
  • Cow dung (approx. 5 kWh/kg dry matter) 1.2 kg
  • Plant residues (approx. 4.5 kWh/kg d.m.) 1.3 kg
  • Hard coal (approx. 8.5 kWh/kg) 0.7 kg
  • City gas (approx. 5.3 kWh/m3) 1.1 m3
  • Propane (approx. 25 kWh/m3) 0.24 m3

The biogas generated from small and medium sized units (up to 6m3) is generally used for cooking and lighting purposes. Large units and/or communal units produce this gas in large quantities and can be used to power engines and generators for mechanical work or power generation.

2. Transformation of organic wastes into high quality organic fertilizer

The polythene bio gas digester is fed with cow dung slurry at a design rate, which is governed by local parameters. The output from the digester (digested manure) is actually a high quality organic fertilizer.

This fertilizer is very important, especially in a country like India where the farmers do not have the resources to buy chemical fertilizers frequently. It has been calculated through KARI lab tests that the fertilizer which comes from a bio-gas plant contains three times more nitrogen than the best compost made through open air digestion. If you compost chicken manure, for example, the finished compost will have in it only 1.58 to 2%o nitrogen. The same manure digested in a bio-gas plant will analyze 6% nitrogen.

Assuming that the digested slurry is immediately utilized - and properly applied - as fertilizer, each daily kg can be expected to yield roughly 0.5 kg extra nitrogen, as compared with fresh manure. If the slurry is first left to dry and/or improperly applied, the nitrogen yield will be considerably lower.

This nitrogen is already present in the manure. The nitrogen is preserved when waste is digested in an enclosed bio-gas plant, whereas the same nitrogen evaporates away as ammonia during open air composting. The bio-gas plant does not make extra nitrogen; it does not create nitrogen, it merely preserves the nitrogen that is already there.

bio gas plant is the perfect fertilizer-making machine and it has been tested all over the world. There is no better way to digest or compost manure and other organic material than in a bio-gas plant. One can compare the bacteria in a digester tank to fish worms. Fish worms help the soil by eating organic matter, passing it through their bodies and expelling it as very rich fertilizer. They live by breaking waste material down into food for plants. It is the same with the bacteria in a methane digester.

Bio-fertilizer is a 100 % natural and organic fertilizer, based on composted organic material (=> renewable energy source). The composting process is achieved through microbe activity and contains all the nutrients and microbe organisms required for the benefits of the plants.

Bio-fertilizers also secrete growth promoting substances like hormones, vitamins, amino acids and anti-fungal chemicals, as well as improve seed germination and root growth. Bio-fertilizers, thereby also aid in the better establishment of plants.

Bio-fertilizers are cost effective and eco-friendly supplements to chemical fertilizers. They provide a sustainable source for nutrients and healthy soils. Each biogas plant produces about five ton's of bio-fertilizer annually, which can replace chemical fertilizer.

3. Health benefits of biogas and the improvement of hygienic conditions (reduction of pathogens, worm eggs and flies)

Biogas can have significant health benefits. According to the Integrated Environmental Impact Analysis carried out for 600 biogas users and 600 non-users, four percent more non-biogas users have respiratory diseases than those who own biogas plants (1). Qualitative information from various household surveys carried out by has revealed that problems like respiratory illness, eye infection, asthma and lung problems have decreased after installing a biogas plant (Tables 1 & 2).

Table 1: Health benefits of biogas


Problems in the past (HHs)*

Present status of HHs




Remained same

Eye Infection





Cases of burning





Lung problem





Respiratory problems




















Table 2 Health benefits of biogas (2)














Chest pain







Respiratory disease










Total (%)





I have included this information which is an extract from the research on households in the country conducted under the GTZ programme to establish the health benefits of biogas to the users after they started using biogas. It can therefore be a better guideline to enable you understands the health benefits of the biogas plant to the cooks in the prison once they start using biogas.

According to the Biogas Users’ Survey conducted in 2000 with 100 households, biogas can have positive impacts on the health of its users. Out of 42 respondents who had respiratory problems in the past, it was reported that the problem has improved for 34 of them. Similarly, those who had problems like asthma, eye infections and lung problems found that their problems had decreased after displacing dirtier fuels with biogas.

If parasitic diseases had previously been common, the improvement in hygiene also has economic benefits (reduced working time). The more fully the sludge is digested, the more pathogens are killed. High temperatures and long retention times are more hygienic.

The following are the principal organisms killed in biogas plants:

o Typhoid

o Paratyphoid,

o Cholera and dysentery bacteria (in one or two weeks),

o Hookworm and bilharzia (in three weeks).

o Tapeworm and roundworm die completely when the fermented slurry is dried in the sun.

The availability of biogas can have effects on nutritional patterns too. With easy access to energy, the number of warm meals may increase. Whole grain and beans may be cooked longer, increasing their digestibility, especially for children. Water may be boiled more regularly, thus reducing waterborne diseases.

4. Reduction of workload, mainly for women, in firewood collection and cooking.

Biogas Plants units (BGU) have many benefits and address many problems. To gather wood, people can spend up to 2-4 hours per day searching and carrying the firewood. Once a BGU is installed, one will have that much extra time to do other things. This will help in improving the quality of lives .

Biogas plants also improve health conditions in the homes:

  • Since biogas burns clean, homes do not fill with smoke and ash.
  • Women and children experience less bronchial problems and can expect to live longer.
  • Homes are also more hygienic.
  • Dung cakes are no longer stored in the homes.
  • Cooking with gas takes less time than with wood or charcoal or any other commonly used fuel.
  • It is easier to cook with gas stove.

The annual time saving for firewood collection and cooking averages to almost 1000 hours in each household provided with a biogas plant.

5. Environmental advantages: through protection of forests, soil, water and air.

Estimating an average per capita consumption of 3 kg of wood per day for energy (cooking, heating and boiling water) in rural areas, the daily per capita demand of energy equals about 6 kWh which could be covered by about 1m3 of biogas. A biogas plant therefore directly saves forest.

For the case of meru prison biodigetser, it can generate an average of 20,000 litres of biogas per day (20m³). It can therefore save about 60kgs of firewood per day, which translates to about 21,900kgs of firewood per year (approx. 21tonnes of firewood per year)

Such a biogas system with a volume of 124 cubic meters can save as much as 9.6 acres of forest (woodland) each year. A recent study has shown that each such a biogas plant can mitigate about 165 tonnes of carbon dioxide equivalent per year.

The credits thus earned could provide alternative financing for the sustainability of biogas program in that particular region.

The widespread production and utilization of biogas is expected to make a substantial contribution to soil protection and amelioration. First, biogas could increasingly replace firewood as a source of energy. Second, biogas systems yield more and better fertilizer. As a result, more fodder becomes available for domestic animals. This, in turn, can lessen the danger of soil erosion attributable to overgrazing.

6. Global Environmental Benefits of Biogas Technology

The greenhouse effect is caused by gases in the atmosphere (mainly carbon dioxide, CO2) which allow the sun’s short wave radiation to reach the earth surface while they absorb, to a large degree, the long wave heat radiation from the earth’s surface and from the atmosphere.

Due to the "natural greenhouse effect" of the earth’s atmosphere the average temperature on earth is 15°C and not minus 18°C.

The increase of the so called greenhouse gases which also include methane, ozone, nitrous oxide, etc. cause a rise of the earth's temperature. The World Bank Group expects a rise in sea levels until the year 2050 of up to 50 cm. Flooding, erosion of the coasts, salinization of ground water and loss of land are but a few of the consequences mentioned.

Until now, instruments to reduce the greenhouse effect considered primarily the reduction of CO2-emissions, due to their high proportion in the atmosphere. Though other greenhouse gases appear to be only a small portion of the atmosphere, they cause much more harm to the climate.

Methane is not only the second most important greenhouse gas (it contributes with 20% to the effect while carbon dioxide causes 62%), it has also a 25 times higher global warming potential compared with carbon dioxide in a time horizon of 100 years. The Bio gas plant effectively reduces the amount of methane directly released into the atmosphere, by trapping it and facilitating its use as a green fuel. After burning, methane only releases harmless gases in air. Given below are the figures relating to this:

With anaerobic digestion, a renewable source of energy is captured, which has an important climatic twin effect:

1. The use of renewable energy reduces the CO2-emissions through a reduction of the demand for fossil fuels.

2. At the same time, by capturing uncontrolled methane emissions, the second most important greenhouse gas is reduced:

1m3 cattle manure = 30 m3 biogas = 194.6 kWh gross = 48kg CO2- emissions

Smaller agricultural units can additionally reduce the use of forest resources for household energy purposes and thus slow down deforestation, soil degradation and resulting natural catastrophes like flooding or desertification.

1 m3 biogas (up to 65% CH4) = 0,5 l fuel oil = 1,6 kg CO2

1 m3 biogas = 5,5 kg fire wood = 11 kg CO2

The reduction of 1 kg methane is equivalent to the reduction of 25 kg CO2. The reduction of greenhouse gases with a high global warming potential can be more efficient compared with the reduction of CO2.

As CO2 generation by burned biogas only amounts to 80 per cent of the CO2 generation of fired fuel oil (per kWh electrical energy) and is even more advantageous in relation to coal (about 50 per cent), the environmental benefits of biogas in relation to fossil fuels are indisputable.

Because of the high cohere efficiency of wood (0.7 kg CO2 per kWh gross energy), the substitution of the wood based biomasses by biogas rise the national and global storage capacity of CO2.

Thus, using biogas has a direct and telling effect on local, regional and global atmosphere, by considerably reducing the greenhouse effect.


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