Green Fuel: Why Is Biogas So Important?

Biogas is a gaseous green fuel that is produce when organic matters like animal manure and plant materials decay in an air-tight chamber called a biogas/anaerobic digester. Biogas contains mainly methane (CH4), carbon dioxide (CO2) and small percentage of hydrogen sulphide (H2S). In a world plagued by environmental, economic and health problems as a result of the use of fossil fuel, replacing fossil fuels with green fuels like biogas will help in alleviating these problems as follows.

1. Methane Capture: When piles of organic matter decay, they give off some methane into the atmosphere. Methane is a powerful greenhouse gas that is about 21 times more effective in trapping heat from the earth than carbon dioxide. This simply means that methane is 21x worse than CO2. Once released, methane can remain in the atmosphere for as long as 15 years!

Apart from carbon dioxide, methane is another gas that is causing the rise in temperature we’re experiencing today. This rise in temperature has led to a chain of other disasters like the rise in sea level due to melting of the polar ice cap. This in turn led to flood in regions close to the sea. It also cause changing weather pattern.

We can reduce the effects of all these woes by treating our organic wastes from our homes, farms, industries etc. with biogas digesters to produce biogas and organic fertilizer. By doing so, the methane that would have been released into the environment will be trapped and converted to CO2 by burning.

Biogas from a small-scale digester is mainly used for cooking while that from a large-scale digester can be used for heating, generating electricity or driving IC engines. In each of these cases, the biogas will be burnt and carbon dioxide produced. Carbon dioxide is a greenhouse gas but it is less effective in trapping heat than methane. If the biogas was derived from plant material, then the carbon dioxide that is released is the one the plants have taken from the atmosphere during photosynthesis. But if it was derived from animal wastes, then we are converting the more effective greenhouse gas, methane, into a less dangerous carbon dioxide. Whichever way, they will all reduce the effect of global warming.

2. Less Carbon dioxide Emission: If most fossil fuels were to be replaced by biogas, the carbon dioxide emission will be drastically reduced. Biomethane – which is a purified biogas containing about 95% CH4 and only 5% CO2 – has a CO2 emission intensity of 11. Whereas the CO2 emission intensity is 67.9 for natural gas, 95.8 for diesel and 96.7 for gasoline.

3. A Source of Green Energy: Biogas is an excellent source of clean energy for cooking, lighting, irrigation and electricity generation. It can replace firewood and thus help to conserve forests and save people the labour of fetching firewood. Biogas can also be upgraded and used to power natural gas vehicles and diesel engines. Countries like Sweden, Germany and Switzerland are already using biogas-powered vehicles.

Some engines are specifically designed to use biogas without any purification. These types of engines are called gas-otto engines/biogas engines. They can operate on biogas containing as low as 45% methane. Diesel engines can be easily converted into dual-fuel engines, so they can use up to 80% biogas and 20% diesel. The simplest of such conversion involves attaching a gas mixer to the air inlet of the diesel engine. When the biogas supply has finish, the engine can automatically revert back to use only diesel. Dual-fuel engines cannot make use of only biogas. They need a little diesel to start the combustion process during the power strokes.

4. Source of Organic Fertilizer: The remains of the organic material (feedstock) left after passing through the digester is called the digestate/ digested slurry. During digestion, carbon, hydrogen and oxygen in the feedstock are used to produce biogas. But the nitrogen, potassium, phosphorus and some other nutrients are left behind. These nutrients are in a form that plants can easily absorb. The fertilizing quality actually depends on the source of the feedstock. For example, the digestate from pig manure is more fertile than that from cow manure.

Application of the raw feedstock as fertiliser can cause burning of plant leaves, caused by low-density fatty acids in the feedstock such as acetic acid. Anaerobic digestion breaks most of the fatty acids and prevents plant burns. Digestate flows more easily off the aerial parts of the plants compared to raw slurry. This reduces the risk of leaf damage.

5. Odour Reduction: The problem of offensive odour from animal wastes has always been the bane of livestock farmers. A biogas digester can help solve this problem. Once the organic waste is inside the digester, any odour is trapped inside. The digestate coming out from the digester has a relatively non-offensive odour. Exposing it to air for about 12 hours will eliminate any offensive odour left. The longer the retention time (the number of days the feedstock remain inside the digester), the less offensive will the digestate odour be. Digesters can reduce odour by up to 80%.

6. Weed and Pathogen Reduction: The temperature and chemical condition inside the digester helps to kill weed seeds and pathogens (disease-causing organism). So when the digestate is applied in the farm, there won’t be a problem of weed growth and transfer of pathogens to man and animals. The digester helps to eliminate a great percentage of the weed and pathogens present in the feedstock.

7. Job Creation: The construction of biogas digesters helps to reduce the rate of unemployment. It creates job opportunities for masons, engineers, marketers of biogas products, operators etc.

Revenue can be generated from the sale of electricity generated from biogas, sales of digestate as fertilizer, soil amendment and animal bedding. Revenue can also come from green energy and carbon credits.

Finally, biogas alone cannot fully address the problem of environmental degradation, but it can go a long way in minimizing the effects. When combined with other green fuels, our environment will be regenerated. If you have a livestock or poultry farm, why not consider passing the manure through a biogas digester? This will be attractive if you have a crop farm close-by where you can apply the slurry on. Transporting slurry over long distance may not be wise economically because of the high water content.

I have written other articles on biogas – articles that contains tips that will help ensure that you succeed. Check them out: Biogas Success.

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