Biogas Project

UTILIZATION OF FARM WASTE IN BIOGAS PRODUCTION

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 digesters

The Biogas Digester is at the heart Anaerobic Digestion (AD) Process, and within the digester fermentation takes place to produce methane gas (biogas), and a liquid and a solid fibrous “digestate” is produced as the residue after digestion has taken place, which is then removed from the digester. Digesters are completely sealed vessels which are covered and sealed. Most are insulated and heated, and the digester is a recognisable at most large biogas plants as a large tall, usually vertical sided, circular tank, with an access ladder and a number of pipes leading to the top where there is also usually a pedestrian access way and handrail.

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 tropospheric 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 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.

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 university lab tests in India 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.

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-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

Biogas can have significant health benefits. According to the Integrated Environmental Impact Analysis, 4% more non-biogas users have respiratory diseases than those who own biogas plants.


Table 1 Health benefits of biogas

Disease 20 80
Cough 53 47
Headache 33 3 67
Nausea 5 95
Chest pain 15 1 85
Lethargy 11 89
Respiratory disease 41 59
Malaria 8 2 92
Typhoid10 10 90
Total (%) 22 1 77
Source: Biogas Users’ Survey,1999 ,BSP**

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

Biogas units have many benefits and address many problems. To gather wood, women can spend up to 2-4 hours per day searching and carrying the firewood*. Once a BGU is installed, she will have that much extra time for herself and her children. This will help in improving the quality of women’s and children’s lives .They will now have more time for education and interesting activities outside the home.

Biogas plants also improve health conditions in the homes:

o Since biogas burns clean, homes do not fill with smoke and ash.
o Women and children experience less bronchial problems and can expect to live longer.
o Homes are also more hygienic.
o Dung cakes are no longer stored in the homes.
o Cooking with gas takes less time than with wood or charcoal or any other commonly used fuel.
o 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 13 kWh which could be covered by about 2 m3 of biogas*. A biogas plant therefore directly saves forest.
Annually, each biogas plant can save more than four ton's of firewood and 32 liters of kerosene*.

A single biogas system with a volume of 100 cubic feet (2,8 m3) can save as much as 0.3 acres (0,12 ha) of forest (woodland) each year*.

A recent study by Winrock**, Nepal and others found that each biogas plant can mitigate about five ton's of carbon dioxide equivalent per year.

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


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.