Microbes in Production of Biogas: We have seen many macroscopic plants and animals around us. Are microbes helpful in human welfare? And which microbes are responsible for the production of biogas? The bacteria that produce a mixture of gases are collectively called methanogens, and one such common bacterium is Methanobacterium. Microbes are present everywhere -in soil, air, water, inside our bodies, outside in the environment, etc.

Microbes not only cause diseases, but they are also helpful in fermentation, formation of curd, sewage treatment, microbes in the production of biogas, etc. There are many steps followed that take place in the biogas plant. Let’s explore more how microbes are helpful in the production of biogas and what are the uses of biogas in this article.

What is Biogas?

Biogas is a mixture of gases produced by the various processes of microorganisms or microbial activity and which may be used as fuel. Cow dung is the chief source for biogas as the bacteria in dung have more potential than others. Cow dung has high levels of nitrogen content and, due to pre-fermentation in the stomach of a ruminant, and has been followed to the most suitable material for the great yield of biogas. The type of gas generated depends upon the microbes and the organic wastes they utilize.

Biogas largely comprises methane and carbon dioxide. A minimal amount of water vapour and Hydrogen sulphide is also present in biogas. Wastewater, food scraps, animal excreta, and sewage, etc., are a few organic matters that can give rise to biogas by anaerobic digestion. Due to the huge content of methane in biogas (typically 50-75%), biogas is flammable and therefore produces a deep blue flame when burnt since the gas is rich in methane and can be used as a renewable energy source.

Composition of Biogas

Name of the Gas	Composition of Biogas in Percentage
Methane (CH4)	50-70
Hydrogen (H2)	5-10
Carbon dioxide (CO2)	30-40
Nitrogen (N2)	1-2
Water vapour (H2O)	0.3
Hydrogen sulphide (H2S)	Traces

Role of Microbes in Production of Biogas

1. Microbes compose various types of gaseous end-products during growth, development, and metabolism.
2. The specific bacteria that grow anaerobically on cellulosic substances produce large amounts of methane along with carbon dioxide, hydrogen sulphide, etc.
3. The bacteria that produce a mixture of gases are collectively called methanogens, and one such common bacterium is Methanobacterium. The above bacteria mentioned are commonly found in the anaerobic sludge during sewage treatment. Methanobacteria is also present in the rumen of cattle. Rumen stores food that is rich in cellulose. These bacteria in rumen help in the breakdown of cellulose and play an important role in the nutrition of cattle.
4. The dung of cows or cattle, commonly called gobar, is rich in these bacteria. Dung can be utilized for the generation of biogas, often called gobar gas.

Biogas Plant and its Components

The biogas plant is a dome-like structure that is made up of brick and cement. The biogas plant consists of five important components or sections in which the biogas plant is mainly designed.

1. Mixing Tank: The various forms of biomass are mixed with an equal quantity of water in the mixing tank. The mixing of cow dung along with the water is called slurry.

2. Inlet Pipe:  Inlet pipe helps in allowing the slurry to feed into the digester.

3. Digester: The digester is a concrete tank that is set 10-15 feet deep inside the earth’s surface. When the digester is fractionally filled with the slurry, the introduction of slurry is prohibited, and the biogas plant is left unused for about two months. Throughout the period of two months, anaerobic bacteria present in the slurry decompose or ferment the organic wastes in the presence of water. As an outcome of anaerobic fermentation, biogas is formed, which starts collecting in the dome of the digester.

4. Outlet Pipe: As more and more biogas starts collecting, the pressure exerted by the biogas forces the spent slurry into the outlet pipe.

5. Overflow Tank: From the outlet chamber, the spent slurry overflows into the overflow tank. The remaining or the residue of the slurry is manually removed from the overflow tank and used as manure for plants. The connections of the gas pipelines are opened when a supply of biogas is required.

Factors Involved in Biogas Production

In the production of biogas, there are many physical, chemical, and biological factors that are involved.

1. C/N Ratio: The C/N ratio is nothing but the ratio of carbon and nitrogen present in the feed material. It is a very important factor in balancing a perfect environment for digestion. The optimum condition for anaerobic digestion to take place ranges from 20 to 30:1. When there is an excessive amount of carbon in the raw wastes, nitrogen will be utilized up first, and carbon will be leftover. This will make the digestion decline and eventually stop. The remaining nitrogen will combine with hydrogen to form ammonia. This can kill or inhibit the growth of bacteria, especially methane producers.

2. Temperature: The rate of temperature affects the rate of reaction happening inside the digester. Hence, the required temperature should be maintained throughout the production process of biogas. Increase in the atmosphere temperature, the rate of reaction, thus increasing the biogas production as well. Methane bacteria are active at a temperature of 350 – 380 C.

3. Retention Time: Retention time is a theoretical time in which the particular volume of feedstock remains in the digester. The anaerobic reaction takes place in the digester.

4. Loading Rate: The amount of raw material fed to the digester per day per unit volume is known as the loading rate. If the reactor is overloaded, the acid collection will be more distinctly affecting daily gas production. On the other hand, underloading of digester has a negative impact on designed gas production.

5. Toxicity: Though small quantities of mineral ions such as potassium and sodium stimulate the development of bacteria, the high concentration of heavy metals and detergents harm the gas production rate. Detergents like antibiotics, soaps, and organic solvents are toxic to the development of microbes inside the digester. The addition of these substances along with the feedstock should be avoided.

6. Total Solid Content: The raw cow dung consists of 80-82% of dampness. The balance of 18-20% is termed total solids. The cow dung is mixed generally in the proportion of 1:1 to bring the total solid content to 8-10%. This adjustment of total solid content helps in digesting the materials at a faster rate and also in deciding the mixing of the various crop residues as feedstocks in a biogas digester.

7. Degree of Mixing: Bacteria in the digester have very limited reach to their food. It is necessary that the slurry is adequately mixed and bacteria get their food supply. It is seen that slight mixing enhances the fermentation; however, a violent slurry agitation retards the digestion.

Uses or Advantages of Biogas

1. Biogas is safe and cheap; hence, it is used for cooking, lighting, etc. Biogas cooking burns with blue flame without any odour or soot, which is considered a vital advantage compared to old cooking fuel like firewood and cow dung cakes.
2. Biogas mantle lamps consume 2-3 cft per hour, having a lighting capacity equivalent to 40 W electric bulbs at 220 volts.
3. Biogas can be used as engine fuel.
4. It is easy to generate since the technology used is cost-effective (low cost).
5. Biogas is an eco-friendly and renewable source of energy.
6. It reduces pollution.
7. The waste left after the biogas production can be used as natural or organic fertilizer for plants.

Summary

Microbes are an extremely important component of life on earth. Not all microorganisms are infectious. Many microorganisms are very useful to mankind. Methanogens produce methane (biogas) while degrading plant waste. Biogas plants are set much in the rural areas because the availability of cow dung and plant waste, straw, weeds, algae, etc., is huge.

Biogas plant mainly consists of five main parts in their design, and they are mixing tank, inlet pipe, digester, outlet pipe, and overflow tank. Biogas produced by microorganisms is used for cooking, lighting, fuel for engines, etc. They are not harmful like LPG gas since they soon dilute in the atmosphere. The usage of biogas helps in reducing the environmental pollution.

FAQs

Q.1. What bacteria produce biogas?
Ans: The group of methane-producing anaerobic bacteria, also called methanogens, are mainly responsible for the production of biogas.

Q.2. What are the benefits of biogas?
Ans: The benefits of biogas are listed below:
1. Biogas decreases water and soil pollution.
2. Biogas saves women’s and children energy from the collection of wood from forests.
3. The machinery used in the production of biogas is low cost.

Q.3. What is the working of a biogas plant?
Ans: The biogas plant is made up of a concrete tank and placed 10-15 feet deep in which organic wastes are collected, and a slurry of dung is force-fed. A floating cover is placed upon the slurry, which keeps on increasing as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet pipe or a chamber, which is connected to a pipe to supply biogas to nearby homes. The spent slurry is separated through another outlet and may be used as manure.

Q.4. Is biogas better than LPG?
Ans: Yes, biogas is better than LPG. Biogas dissolves in the air quickly as the biogas is lighter than air and is much safer in homes than CNG or LPG.

Q.5. What are the types of biogas?
Ans: Floating drum type, fixed dome type, balloon plants, earth-pit plants, Ferro-cement plants, etc., are the different types of biogas plants.

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