What is Biogas?
Biogas is a renewable energy source. It is produced under anaerobic conditions by breaking down organic matters such as agricultural waste, food waste and animal dung by a specific bacteria. Biogas is produced in a bio gas plant. The major components of biogas are primarily methane (CH4), hydrogen (H) and carbon dioxide (CO2). As the decomposition of these organic matters happens in an anaerobic environment, the process is also termed as anaerobic digestion. One of the major components of biogas is methane, which constitutes about 50-75% of the biogas. Thus, it is highly flammable, and produces a deep blue flame. Biogas is also used to power various types of vehicles.
Bio Gas Plant
The anaerobic digesters we have mentioned earlier are called biogas plants. In this section, we will have an introduction of a biogas plant. A working bio gas plant has about five components- an inlet, a fermentation chamber, storage, an outlet and finally one exit pipe. The inlet is a path through which the slurry is fed to the consequent chamber, where the biogas reactors are at work which is otherwise known as the fermentation chamber. In this chamber, many biogas reactors or microorganisms play the role of a chef; they break down the organic matter to produce the biogas. Then the produced gas is stored in the storage tank from where the gas is channelled through the exit pipe. The outlet is used to clear out the fermentation chamber. A biogas plant diagram looks like this -
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Breakdown of Organic Waste
Organic wastes such as agricultural waste, food waste or animal dung are first processed as a liquid or as slurry, which is mixed with water, and then they are fed to the bio gas plant. Now the stages are as follows-
The polymers of the organic waste are broken down in the first step, to make it more susceptible to the acidogenic bacteria present in the next step.
In this step carbon-di-oxide, ammonia, hydrogen and other organic acids are produced as the acidogenic bacteria convert the sugar and amino acid from the broken down organic waste.
These organic acids are further converted into hydrogen, ammonia and carbon-di-oxide.
All these are ultimately converted into methane and carbon-di-oxide, by methanogens.
Methane is a highly combustible gas and can also be oxidized with oxygen. The energy produced by the combustion of these gases can be used in various ways and can be used as fuel.
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The Ecology of Biogas
Biogas is one of the most environmentally friendly energy sources. It takes care of the two harmful effects of fossil-fueled energy sources. We have been relying on fossil fuels for energy sources since the dawn of modern civilization. But it won't be easy to make ends meet if we keep on welling fossil fuel as our only energy source. Along with water pollution, air pollution, fossil fuel energy sources are a curse to mankind and the environment as well. By converting organic waste which is mass-produced in every household, in a reliable energy supply, we can alleviate both harmful effects at one. On the one hand, keep the fossil fuel depletion at bay and also cleanse the environment. Biogas takes harmful gases like methane and carbon-di-oxide and converts them into a much safer form.
Solved Examples
1. What is Biogas?
Biogas is a renewable energy source. It is produced under anaerobic conditions by breaking down organic matters such as agricultural waste, food waste, and animal dung by a certain bacteria. It is also environment-friendly.
2. Fill in the blanks the main component of biogas is______?
Methane
3. Name the components of biogas.
The components of biogas are- methane, carbon-di-oxide, hydrogen, nitrogen and other gases.
Did You Know?
The major components of biogas are methane and carbon-di-oxide. A bio gas plant has five components, an inlet, a fermentation chamber, storage, an outlet and finally one exit pipe. Biogas is a renewable energy source; it is also environment - friendly. In 2016, the amount of biogas obtained from households in the UK provided for 2 million families. 36% of the renewables collected throughout the world come from biogas.
FAQs on Biogas
1. What is biogas and why is it considered a renewable source of energy?
Biogas is a mixture of gases produced by the breakdown of organic matter in the absence of oxygen, a process known as anaerobic digestion. It primarily consists of methane (50-75%), carbon dioxide (25-45%), and trace amounts of other gases. It is considered renewable because it is derived from organic waste like agricultural residue, animal dung, and food scraps, which are continuously available.
2. What are the main components of a typical biogas plant?
A typical biogas plant, as prescribed in the NCERT syllabus, has the following key components:
- Inlet: A chamber for mixing raw materials like dung and water to form a slurry.
- Digester Tank: A large, sealed underground tank where the anaerobic digestion takes place. It is typically 10-15 feet deep.
- Gas Holder/Dome: A floating or fixed dome on top of the digester to collect the produced biogas. As gas accumulates, the dome rises.
- Gas Outlet Pipe: A pipe connected to the gas holder to transport the biogas for use in kitchens or for lighting.
- Outlet/Overflow Tank: A section where the spent slurry (digestate) is collected after the digestion process is complete.
3. What is the specific role of methanogens in biogas production?
Methanogens are a group of microbes (specifically Archaea) that are crucial for the final stage of anaerobic digestion. They grow anaerobically on cellulosic material and act on the intermediate products formed by other bacteria. Their primary role is to convert acetic acid, hydrogen, and carbon dioxide into methane (CH₄), which is the main combustible component of biogas. Without methanogens, the production of flammable biogas would not occur.
4. How does a biogas plant contribute to both energy production and waste management?
A biogas plant serves a dual purpose. Firstly, it converts organic waste, which would otherwise pollute the environment, into a clean and efficient fuel (biogas) for cooking and lighting. Secondly, the leftover slurry, or digestate, is a nutrient-rich organic manure. This bio-fertiliser can be used to improve soil fertility, reducing the need for chemical fertilisers and completing the nutrient cycle. This integrated system provides energy while simultaneously managing waste effectively.
5. What is the difference between gobar gas and biogas?
The terms 'gobar gas' and 'biogas' are often used interchangeably, but there is a slight distinction. 'Gobar gas' specifically refers to biogas produced using cattle dung (gobar) as the primary raw material. 'Biogas' is a broader term that refers to the gas produced from the anaerobic digestion of any organic matter, which can include agricultural waste, plant material, sewage, and food waste, in addition to animal dung.
6. What are the main uses and benefits of using biogas?
The main use of biogas is as a fuel, primarily for cooking and lighting in rural areas. Its benefits are significant:
- Eco-Friendly: It is a clean fuel that reduces reliance on firewood and fossil fuels, thereby preventing deforestation and air pollution.
- Waste Reduction: It provides a safe and effective way to dispose of organic waste.
- Improved Sanitation: It helps in managing animal and human excreta, improving hygiene.
- Production of Fertiliser: The byproduct, slurry, is an excellent organic fertiliser that enriches the soil.
7. Why is anaerobic digestion essential for producing biogas instead of aerobic decomposition?
Anaerobic digestion (without oxygen) is essential because the specific microbes responsible for producing methane, the methanogens, can only survive and function in an oxygen-free environment. In aerobic decomposition (with oxygen), different microbes break down organic waste, primarily releasing carbon dioxide, water, and heat, but not the flammable methane gas required for fuel. Therefore, the sealed, oxygen-free digester tank is critical for the process.
8. What types of organic matter are best suited for a biogas plant?
A wide variety of organic matter can be used to produce biogas. The most common and effective materials, particularly in the context of the Indian agricultural landscape as per the CBSE curriculum, include cattle dung (gobar), agricultural waste like straw and husks, vegetable waste from markets, poultry droppings, and human excreta. The key requirement is that the material must be biodegradable for the microbes to break it down.
