Biogas: Uses of Biogas

What is Biogas? 

Biogas is also known as gobar gas. The gases produced by anaerobic decomposition of organic matter such as manure, municipal waste, plant material, agricultural waste, cow dung, sewage, food waste, green waste etc. are called biogas. Thus, biogas is not a one gas but instead it is a mixture of gases. 

Cow dung is the main source for production of biogas as it contains many bacteria naturally which help in anaerobic decomposition of organic matter. This is the reason biogas is called gobar gas. Cow dung contains methanobacterium which is found in the rumen of cow’s digestive system. Methanobacterium not only produces methane gas but manure as well by decomposition of bio waste. 

Composition of Biogas

Composition of biogas may vary according to the substrate used and conditions available for anaerobic decomposition of substrate. It contains methane, carbon dioxide, nitrogen, hydrogen, hydrogen sulfide and oxygen. Typical composition of biogas with percentage of its constituent gases can be written as follows –

Gases 

Formula 

Percentage present 

Methane 

CH4

50-70

Carbon dioxide 

CO2

25-50

Nitrogen 

N2

0-9

Hydrogen 

H2

0-1

Hydrogen sulfide 

H2S

0.1-0.5

Oxygen 

O2

0-0.5


Apart from these gases we find water vapor also in biogas. The amount of water vapor depends on temperature, moisture present in the substrate mixture. 

 Sometimes we get following contaminants also in the mixture of biogases –

  • Sulfur Compounds – If sulfur compounds are present in the biogas then combustion of biogas produces sulfur dioxide and sulfuric acid which are corrosive and environmentally hazardous. 

  • Ammonia – If ammonia is present in biogas then combustion of biogas produces nitrogen oxides also which are environmentally hazardous and toxic in nature. 

  • Siloxanes – Siloxanes are compounds of silicon. Sometimes siloxanes are present in the biogas which on combustion produces silicon and silicon combines with oxygen produces oxides of silicon. Oxides of silicon are not good for health. 

Production of Biogas 

Production of biogas has been done since ages. It is very old method of producing fuel and manure using mainly agricultural waste and cow dung. It is done by the reaction of microorganisms such methanogens (archaeans) and eubacteria. Production of biogas basically is the fermentation of biomass which is done anaerobically in presence of moisture. 

It is generally produced at the small scale in rural areas where agricultural is the main profession. An anaerobic digester that treats cow dung and other agricultural waste is called biogas plant. It is generally made up of brick and cement. Typically, it has following parts –

  • Mixing tank 

  • Inlet chamber 

  • Digester 

  • Outlet chamber 

  • Overflow tank 

Mixing tank – It is a medium size tank made up of brick and cement at a height. In this tank cow dung, agricultural waste and other biomass is collected and mixed with water.

Inlet chamber – It is a larger size tank than mixing tank. It is also made up of brick and cement. It connects mixing tank to digester. 

Digester – It is the largest chamber of biogas plant where the process of anerobic fermentation takes place. It has a valve on the top from where the produced biogas is released according to the requirement. 

Outlet Chamber – It is linked to digester. It collects slurry and manure after fermentation. 

Working of biogas plant – Cow dung, dead plants, agricultural waste, food waste etc. various forms of biomass are mixed with an equal amount of water in the mixing chamber or tank. This mixture is called slurry. Now this slurry is moved into the digester through inlet chamber. When digester almost half filled with slurry, the introduction of slurry is stopped. Digester is closed and oxygen is prevented from entering the digester to let fermentation process take place actively. pH level in digester should be neutral or seven while temperature should be 30-35 for maximum yield. Now the plant is left unused for about 2 months. During these two months anaerobic decomposition of organic matter or fermentation takes place. Eubacteria convert organic material into organic acids, alcohols, acetate, carbon dioxide and hydrogen gas. Archaeans produces methane by using acetate or carbon dioxide and hydrogen gas. 

Uses of Biogas  

  • It is commonly used in rural areas as cooking gas.

  • It can be used for the production of electricity. 

  • It can be used in instruments used for water heating, space (room) heating etc.

  • It can replace compressed natural gas for use in vehicles. 

  • It can displace carbon dioxide in on-site CHP plants. 

  • It is being used in the transport. For example, ‘Amanda Biogas Train’ runs on biogas in Sweden.

  • Production of biogas produced a very useful dry solid byproduct which is used as manure. 

  • It is used in many states for street lighting purposes. 

  • It can be used in hydrogen fuel cells as well. 

Advantages of Biogas 

Following are the advantages of biogas –

  • Biogas don’t pollute the environment. Thus, it is eco-friendly fuel. 

  • It is renewable source of energy.

  • It reduces soil, water and air pollution.

  • It produces organic manure as byproduct. 

  • As it is a low-cost method to produce energy, so it is economically friendly as well. 

  • It encourages circular economy and beneficial for all classes. 

  • It is a healthy cooking alternative specially for developing countries. 

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