Envis Centre, Ministry of Environment & Forest, Govt. of India

Printed Date: Sunday, August 18, 2019

Biogas

Biogas is produced by fermenting biomass. It is a gas containing methane, which serves as a renewable and versatile raw material for generating electricity, heat and fuel, thus vitally contributing to a safe and environmentally compatible energy supply. Biogas can be stored or can be fed into the natural gas grid and is therefore extremely flexible.

 

Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste.It is a renewable energy source and in many cases exerts a very small carbon footprint.

 

Biogas can be produced by anaerobic digestion with anaerobic bacteria, which digest material inside a closed system, or fermentation of biodegradable materials. It is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as afuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.

 

At present, biogas technology provides an alternative source of energy in rural India for cooking. It is particularly useful for village households that have their own cattle. Through a simple process cattle dung is used to produce a gas, which serves as fuel for cooking. The residual dung is used as manure. Apart from cattle dung, field crops may also be grown intentionally as an energy crop, and the remaining plant byproduct used as a fuel.

 

Digestion Process

 

The anaerobic digestion of the organic waste matter occurs in three different stages:

 

  • Hydrolysis
  • Acidogenesis
  • Methanogenesis

 

Hydrolysis: Most of the organic waste materials subjected to bio-methanation contain the macromolecules like cellulose, hemicelluloses, lignin etc. which are insoluble in water. In the first step of digestion, these macromolecules are subjected to breakdown into micro-molecules with the help of some enzymes which are secreted by the bacteria. In the initial step, oxygen in the feed materials is used up by oxygen loving bacteria and large amounts of carbon-dioxide (CO2) are released and the major end product of this step is glucose.

 

Acid Formation: The components released during the hydrolytic breakdown become the substrate for the acid forming bacteria. The acid forming bacteria convert the water soluble substances into volatile acids. The major component of the volatile acid is acetic acid. Beside this some other acids like butric acid, propionic acid etc. and gases like CO2 and H2 are also produced. The acid forming bacteria during the conversion process utilize the amount of oxygen remaining in the medium and make the environment anaerobic.

 

Methane Formation: This is the last stage of the biogas generation. In this stage, the methanogenic bacteria convert the volatile acids formed in the second step by the acidogenic bacteria to methane and carbondioxide. Some excess CO2 in the medium is also converted to methane gas by reacting with the hydrogen present in the environment.

 

The end products of Bio-Gas Technology are:

 

Biogas: It is a marsh gas, a mixture of Methane (55-65%), Carbon-dioxide (35-45%), and trace amount of Hydrogen, Hydrogen Sulphide and Amonia. It is a combustible gas and can be used for heating, lighting, powering irrigation pump, generating electric power and for local use for cooking purpose. The gas is smokeless, environment friendly and efficient fuel.

 

Left over slurry: Environmental friendly manure would be produced which can be used as organic fertilizer for gardening and agricultural purpose. It can be used to enrich the soil. It can also be dovetailed to vermin composting to enrich mineral value of compost.

 

Advantages and Benefits of Biogas

 

  • Provides a non-polluting and renewable source of energy.
  • Efficient way of energy conversion (saves fuelwood).
  • Saves women and children from drudgery of collection and carrying of firewood, exposure to smoke in the kitchen, and time consumed for cooking and cleaning of utensils.
  • Produces enriched organic manure, which can supplement or even replace chemical fertilizers.
  • Leads to improvement in the environment, and sanitation and hygiene.
  • Provides a source for decentralized power generation.
  • Leads to employment generation in the rural areas.
  • Household wastes and bio-wastes can be disposed of usefully and in a healthy manner.
  • The technology is cheaper and much simpler than those for other bio-fuels, and it is ideal for small scale application.
  • Dilute waste materials (2-10% solids) can be used as in feed materials.
  • Any biodegradable matter can be used as substrate.
  • Anaerobic digestion inactivates pathogens and parasites, and is quite effective in reducing the incidence of water borne diseases.
  • Environmental benefits on a global scale: Biogas plants significantly lower the greenhouse effects on the earth’s atmosphere. The plants lower methane emissions by entrapping the harmful gas and using it as fuel.

 

Biogas, the Eco Alternative

 

The consumption of non-renewable sources of energy has caused more environmental damage than any other human activity in the last century. Over dependence on fossil fuels such as coal and crude oil, which have been used for electricity generation and other uses have led to high concentrations of harmful gases in the atmosphere that has resulted in ozone depletion and global warming. With fast depleting oil reserves, an energy crisis seems imminent.

 

 

So, what is the solution to this imminent crisis? The best solution would be to revert back to the vedic life style, i.e. a life without electricity and many such modern amenities. But, it would be very difficult to make this sudden transition. The next best option is to opt for some other alternative sources of energy that can offset or at least reduce the problems caused by fossil fuels.

 

Biomass is a renewable energy resource derived from the carbonaceous waste of various human and natural activities. It is derived from numerous sources, including the by-products from the timber industry, agricultural crops, cattle dung, raw material from the forest, major parts of household waste and wood. Biomass does not add carbon dioxide to the atmosphere as it utilizes the same amount of carbon in growing as it releases when consumed as a fuel. In the case of animal wastes and other bio-degradable wastes, it is environmentally more beneficial to convert them into biogas. This is because the biogas, when used for thermal or electricity applications, is converted into carbon di-oxide and released into atmosphere. The same bio degradable waste, when allowed to decompose naturally, would lead to release of methane, which is a much more damaging green house gas as compared to carbon di-oxide.

 

At present, biogas technology provides an alternative source of energy in rural India for cooking. It is particularly useful for village households that have their own cattle. Through a simple process cattle dung is used to produce a gas, which serves as fuel for cooking. The residual dung is used as manure. Apart from cattle dung, field crops may also be grown intentionally as an energy crop, and the remaining plant byproduct used as a fuel.

 

Biogas is produced from bio degradable wastes through a process called anaerobic digestion. During this process, some organic compounds are converted to methane (CH4) and carbon dioxide (CO2) gases. This mixture of gases is known as biogas. The composition of biogas is 50 to 75 per cent CH4 and 25 to 45 per cent CO2. Like natural gas, biogas can also be used as a fuel in power generators, engines, boilers and burners.

 

In practice, specially designed and insulated tanks are used to facilitate the anaerobic digestion process under a controlled atmosphere. These tanks are known as anaerobic digesters or bio digesters. The effluent coming out from the digester after the completion of the digestion process is known as digestate that has high nutrient value and can be used as manure. Digestate also has much less odour compared to stored manure. Some commonly used technologies used for biogas plats are fixed dome, Floating dome and Bag type. A typical Biogas based Power Generation System comprises of Biogas Plant, Gas Cleaning System, Engine with alternator, Control Panel, Machine Room / Shed and Manure management system.

 

Source: ecovillage.org.in