What is biogas?

What is biogas?

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 produced through a natural process called anaerobic digestion (AD). Biogas is a by-product of this process. Organic materials and organic waste are collected, such as agricultural residues, animal manure, food waste, sewage sludge, or energy crops. A biogas plant is often the name given to an anaerobic digestion facility.

What is Anaerobic Digestion?

AD is a safe biological process in which microorganisms break down organic matter in the absence of oxygen. Additionally, it is a naturally occurring process similar to that a cow uses to break down food in its stomach. However, AD can be replicated with carefully engineered methods that use digestion tanks in controlled conditions.

What is the Anaerobic Digestion process?

For anaerobic digestion to occur, specific physical and chemical conditions are necessary to activate the microorganisms and start AD biology. You can read more about Anaerobic Digestion HERE.

To start the biology, the digester tank must be sealed with no oxygen. Furthermore, temperature plays an important role in anaerobic digestion. The temperature of the digester affects the activities of the anaerobic bacteria. For a mesophilic AD plant, a microorganism's optimal temperature ranges between 35°C and 42°C whilst thermophilic processes generally operate between 48-51°C.

From here, biology takes over, and a culture of microorganisms develops and physically digests the materials inside the tank. Subsequently, there are four main biological stages of anaerobic digestion: hydrolysis, acidogenesis, acetogenesis and methanogenesis, which happen over a period of 15 to 60 days. Specific groups of bacteria are more active than others at various stages, and the results from one phase are the input for the subsequent phase of digestion. The digester tank must be continually monitored, and all specific conditions must be maintained throughout the AD process.

The anaerobic digestion process produces two products. The first is biogas that is captured at the top of the digester tank, and the second is a by-product known as digestate.

Anaerobic digestion food waste facility
Anaerobic digestion food waste facility

What are the benefits of biogas?

The stored biogas can be utilised in various ways. Biogas has multiple uses across various sectors. Here are some common applications of biogas.

Combined heat and power (CHP)

Biogas can be used to power a combined heat and power engine (CHP). The engine burns the biogas and uses the energy to turn a generator, thus simultaneously generating electricity and heat. The heat can be used to heat the AD digestion tanks and in the pasteurisation process used for food waste AD. The electricity produced is used to power the AD plant, hence making the plant self-sufficient. In addition, the surplus electricity is supplied to the National Grid to power local homes and businesses.

CHP Engine
CHP Engine

Biomethane (CH4)

Biogas 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. Biomethane is biogas that has had the CO2 and trace gases removed. Various technologies are used to remove carbon dioxide from biogas, including pressure swing adsorption (PSA), water scrubbing, chemical absorption, and membrane separation. These processes separate the methane and carbon dioxide, allowing the carbon dioxide to be captured. It is renewable gas with the same composition as natural gas but is classified as a green alternative to fossil fuel. After carbon dioxide removal, the biomethane can be further enriched to increase its methane content. This step involves adjusting the methane concentration to meet specific requirements or quality standards, such as those set for injection into the Natural Gas Grid. Biomethane can be injected into the National Gas Grid for homes and businesses to use for cooking, heating, and fuelling power stations that deliver electricity to homes and businesses. Biomethane is a renewable energy source because it is derived from organic waste materials that would otherwise release greenhouse gases during decomposition. Utilizing biomethane helps reduce reliance on fossil fuels, decreases carbon dioxide emissions, and contributes to the circular economy by utilising organic waste resources.

BioLPG or Biopropane

LPG, commonly known as propane or butane, is a flammable hydrocarbon gas derived from fossil fuel sources, primarily crude oil refining and natural gas processing.

However, there are renewable alternatives to conventional LPG that are produced from biomass sources. These renewable gases are often referred to as BioLPG or Biopropane. BioLPG is chemically identical to conventional LPG but is produced from renewable feedstocks, such as vegetable oils, animal fats, or organic waste materials.

The production of BioLPG involves processes such as hydrotreating, hydrogenation, and fractionation to transform the renewable feedstocks into a propane-rich gas with similar properties to conventional LPG. BioLPG can be used as a drop-in replacement for conventional LPG in various applications, including heating, cooking, ovens, barbecues, fireplaces, heaters, transportation, and industrial processes.

BioLPG offers environmental benefits compared to conventional LPG since it is derived from renewable sources, reducing reliance on fossil fuels and contributing to greenhouse gas emissions reduction. It can be a part of the transition towards a more sustainable and low-carbon energy system.

Carbon capture (CO2)

When the CO2 is separated from the biomethane, it can be captured and sent for use in the production of fire extinguishers, inflating life rafts and life jackets, encouraging the growth of plants in greenhouses, for carbonated beverages, food manufacturing, abattoirs and medicine preserve.

You can read more about Carbon Capture HERE

Agriculture and farming applications

Biogas can be used in agricultural settings for heating livestock housing, drying crops, and generating electricity to power farm operations. Additionally, the nutrient-rich digestate produced during the biogas production process can be used as a fertilizer for agricultural lands.

You can watch a video about digestate HERE

Digestate spreading
Digestate spreading

History of Biogas

Biogas has been produced naturally 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.

Early pioneer Jan Baptista Van Helmont discovered that decaying organic matter gave off gas, and Count Alessandro Volta noticed that anaerobic activity occurred naturally in nature, followed by the discovery that cattle manure gave off methane gas. These were significant 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 of energy production, anaerobic technology dramatically developed in the early part of the 20th Century.

Today, these fossil fuels dominate the global economy but at a detrimental cost to the environment. Now, as the world realises greenhouse gases must be eliminated, the versatile process of AD is the best technology today for recycling organic matter and producing biogas. Moreover, biogas offers an extensive range of benefits.

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