Biogas Production – Role of Microbes

Microbes in the production of biogas come under the category of useful microorganisms. These microbes help in the production of biogas and are called methanogens. Methanogens such as Methanobacterium are found in the rumen of the cattle. These bacteria produce large amounts of methane, carbon dioxide, and hydrogen when they grow under anaerobic conditions thus producing biogas.

What is Biogas?

A mixture of gases that is produced by various microorganisms called methanogens and which can be used as a fuel is called biogas. Generally, biogas is produced from cattle dung as it is rich in methanogens. It is also rich in nitrogen which gives a good amount of biogas. The composition of biogas and the types of gases present in biogas generally depend upon the chemical content of the waste or dung.

Composition of Biogas

Biogas generally contains methane, carbon dioxide and hydrogen. It also contains a small amount of water vapors and Hydrogen Sulphide gas. The presence of methane in biogas is the reason it is used as fuel because biogas becomes inflammable due to presence of methane and can be used as renewable energy resource. Generally biogas has the following composition:

Gas	Composition of Biogas (%)
Methane	50-70
Carbon Dioxide	30-40
Nitrogen	1-2
Hydrogen	5-10

Role of Microbes In Biogas Production

Role of Microbes in biogas production are given below:

• When microbes grow anaerobically, they produce various types of gases during different stages of growth.
• These gases include methane, carbon dioxide, hydrogen, etc.
• The microorganisms that produce these gases are collectively called methanogens. They are found in the sludge that is produced during sewage treatment. They are found in the stomach of cattle in rumen.
• Thus we make use of cattle dung and other cellulosic wastes to produce gobar gas or biogas.

Production of Biogas

Biogas production takes place in special plants called biogas plant. The structure of a biogas plant is shown below:

A biogas plant generally has 5 main sections which are as follows:

• Mixing Tank: Various types of wastes such as cow dung, plant and animal wastes are mixed in a tank with water. The product formed after mixing these wastes with water is called slurry.
• Inlet Pipe: The slurry is then fed into a tank with anaerobic conditions with the help of a pipe called inlet pipe.
• Digester: It is the main part of the biogas plant. It is constructed 10-15 ft. inside the Earth’ surface and made up o concrete. It is filled with slurry upto a certain limit through the inlet pipe. The slurry in the tank is now left undisturbed for nearly 2-3 months. As the tank has anaerobic conditions, microorganisms present in the slurry can grow here and decompose the waste anaerobically. This leads to the production of gases or biogas.
• Gas Storage Tank: The biogas produced in the digester starts accumulating in the dome of digester which is called gas storage tank.
• Outlet Pipe: As more and more biogas is produced in the digester, it pushes the used slurry in the outlet pipe which is connected to another part called overflow tank.
• Overflow Tank: The used slurry gets collected in the overflow tank. The remaining slurry in the digester is removed manually. This leftover slurry can be used as manure for plants in farms and gardens.
• The gas storage tank has outlet pipes through which biogas can be used as fuel when needed.

Various waste materials that can be fed into the biogas plant are:

• Cattle dung and urine
• Tobacco waste, bagasse, bran
• Algae, Eichhornia
• Straw, fodder, weeds, crop stubble, sticks of cotton and jute
• Paper, domestic waste

Factors Involved In Biogas Production

Biogas production is dependent on various factors such as:

• Carbon-Nitrogen ratio: It is very important to have an optimal ratio between carbon and nitrogen in the waste material or slurry. Generally a ratio of 20:1 is desirable. If there is high carbon content, then nitrogen will be exhausted first and carbon will be leftover in the slurry which will lead to decline in the process of formation of biogas. If there is high nitrogen content, then it may combine with hydrogen produced and form ammonia which can kill the methanogens present in the tank.
• Temperature: Methanogens are active at a temperature of 350-380^o C. Thus it is desirable to maintain an optimum temperature in the tank to increase the production of biogas.
• Retention Time: It is the time period for which the slurry needs to be kept undisturbed in the digester. It is generally 2-3 months but it can vary depending on the other physical and chemical conditions such as temperature and pressure.
• Toxicity: Various heavy metals and soaps and detergents are very harmful for the microorganisms and inhibit their growth. Thus, care should be taken that these materials are not mixed in the wastes fed into the digester.

Advantages Of Biogas

Biogas has following advantages:

• It is a cost efficient and a renewable fuel.
• It burns with a blue flame and thus undergoes complete combustion.
• It can be used for cooking and as an engine fuel.
• It can be easily produced and transported.
• The waste from the biogas plants can be used as manures and organic fertilizers to boost plant growth.

Disadvantages Of Biogas

Biogas has following disadvantages:

• Biogas cannot be used on a large scale as it has low calorific value.
• It is highly corrosive to container when stored in a compressed form.
• It is also prone to explosion as methane in biogas mixes vigorously with oxygen to form pure carbon dioxide and results in explosion.

FAQs on Microbes In Human Welfare- Microbes In Production Of Biogas

1. What is biogas?

Answer:

A mixture of gases that is produced by various microorganisms called methanogens and which can be used as a fuel is called biogas.

2. Which microorganisms help in biogas production?

Answer:

Certain microorganisms called methanogens such as methanobacterium help in the production of biogas.

3. What are the major parts of biogas plant?

Answer:

Major parts of a biogas plant are:

• Mixing Tank
• Inlet Pipe
• Digester
• Gas storage tank
• Outlet pipe
• Overflow tank

4. State two advantages of biogas.

Answer:

Advantages of biogas are:

• It is a cost efficient and a renewable fuel.
• It burns with a blue flame and thus undergoes complete combustion.

5. State the factors that affect biogas production.

Answer:

Factors that affect biogas production are:

• Carbon-Nitrogen ratio
• Toxicity
• Temperature
• Retention Period

6. State two disadvantages of biogas.

Answer:

Disadvantages of biogas are:

• Biogas cannot be used on a large scale as it has low calorific value.
• It is highly corrosive to container when stored in a compressed form.