Biogas is a renewable gas made of a mixture of methane (CH4), carbon dioxide (CO2), water vapour, and trace amounts of other gases.
How is biogas made?
Biogas is made when microorganisms decompose organic matter, in the absence of oxygen and light, in a series of biological processes. These processes are known as anaerobic digestion.
What is anaerobic digestion?
AD is a naturally occurring process similar to that a cow uses to break down food in its stomach. Carefully engineered processes using digestion tanks in controlled conditions can replicate this process on a large scale.
What is the anaerobic digestion process?
Firstly, the organic matter is treated to obtain a standardised substrate that is fed into the anaerobic digesters. Then, inside the digesters, the substrate is gently heated and stirred continuously. The substrate breaks down over a period of 15 to 60 days, generating biogas. You can read more about Anaerobic Digestion here.
The AD process extracts energy from the organic matter in the form of biogas and fertiliser in the form of digestate, a residual material composed of liquid and solid.
The biogas is captured in the roof of the digester tank and can then be used to generate electricity, produce heat, injected into the gas grid, or used as an LPG.
The organic matter or waste, often used in the AD process, is typically food waste, green waste, agricultural waste, manure, municipal waste and sewage sludge.
What are the benefits of Anaerobic Digestion and Biogas?
Anaerobic digestion is known for producing renewable energy. Still, there are far more benefits, such as recycling organic waste and reducing the environmental impact of harmful methane gases. AD can also help stop water pollution, generate heat, provide jobs and give back to the land.
Every year, 1.3 billion tonnes of food is either lost or wasted worldwide, says the United Nations Environmental Programme (UNEP) Food Waste Index. Food waste and other dumped organic wastes release harmful Green House Gases (GHG) into the atmosphere. AD can recycle organic matter and cut total GHG emissions by capturing the methane from organic waste breakdown and turning it into biogas. AD can process not just food waste but sewage sludge, livestock manure and crop residues.
Renewable energy supply
AD replaces the need to use non-renewable natural gas that, when burned, releases methane into the atmosphere. Instead, the biogas produced from the AD process can be turned into a more versatile fuel called biomethane. Two essential steps are required to transform biogas into biomethane. The first is a cleaning process to remove the trace components, and the second is an upgrading process to adjust the calorific value. Once this is completed, biomethane can be used to replace natural gas and supplied to thousands of homes and businesses.
The conversion of biogas to fuel for transportation provides an alternative to fossil fuels. Biogas can be upgraded to liquid bio-LNG or compressed bio-CNG and used throughout the transport sector. Because bio-LNG and bio-CNG have almost an identical chemical composition to LNG and CNG, they can be used in cars, lorries and heavy-duty transport vehicles as a renewable energy source.
Giving back to the earth
The organic matter left over from the AD process, known as digestate or bio-fertiliser, is rich in nutrients such as nitrogen, phosphate and potash. These nutrients can be returned to the soil when used as fertilisers by farmers instead of petrochemical fertilisers, which are costly to the environment and made from manufactured chemicals. This process contributes to the circular economy.
Reducing methane emissions
When organic waste is left untreated, it releases large amounts of methane into the atmosphere. The process of AD captures this methane.
When the bi-CO2 is separated from the bio-methane, it can be sent for use in the production of fire extinguishers, inflating life rafts and life jackets, encouraging the growth of plants in greenhouses and carbonated beverages.
History of Biogas
Anaerobic Digestion has been happening in nature for years. Evidence suggests that biogas was used for heating bath water in the 10th century BC, and the first digestion plant was built in Bombay, India, in 1859. Next, early pioneer, Jan Baptista Van Helmont discovered that decaying organic matter gave off-gas. Then, Count Alessandro Volta noticed that anaerobic activity occurred naturally in nature, followed by the discovery that cattle manure gave off methane gas. These were historical developments for Anaerobic Digestion.
With the start of the Industrial Revolution, Anaerobic Digestion was set aside as coal and other fossil fuels were used to drive new power and machinery. For the past 100 years, the world has depended on fossil fuels to produce a large amount of energy at a low cost. In addition, these resources have enabled worldwide travel and the creation of products on a mass scale. However, although not at the forefront, anaerobic technology dramatically developed in the early part of the 20th Century.
Today, the global economy remains dominated by these fossil fuels but at a detrimental cost to the environment. Now, as the world realises GHG must be eliminated, the versatile process of AD is the best technology today for recycling organic matter and producing biogas. Biogas offers an extensive range of benefits.