The energy hidden in manure: What is biogas?

Did you know that it is possible to generate completely renewable energy by taking advantage of organic waste? It is a cheap source of energy, reducing waste and pollution created by other fuels. But let's take a closer look at what biogas is and how it works.

What is biogas?

As defined by the Spanish Institute for the Diversification and Saving of Energy (IDAE), biogas "is a gas composed mainly of methane and carbon dioxide, in variable proportions depending on the composition of the organic matter from which it is generated". It is a gas that occurs naturally in places where there is decomposition of organic matter, but there is no oxygen, such as swamps.

At an industrial level, imitating and enhancing the processes of nature, biogas is mainly obtained from livestock and agro-industrial waste, from sludge from urban wastewater treatment plants and from the organic fraction of household waste.

What is biogas used for?

Biogas is considered a renewable energy source and is the only one that can be used for all major energy applications: electricity generation, heat generation or as fuel. It can also be piped directly for use in a domestic boiler or adapted cooker, as is the case in the Bolivian highlands. In addition, it can be subjected to industrial processes to be enriched (raising the proportion of methane to 90%) and thus injected into natural gas transport and distribution infrastructures. In this case, the enriched gas is called biomethane.

How is biogas produced?

Both in nature and at an industrial level, the biogas generation process has four stages:

1. Hydrolysis: here, a series of enzymes break down complex particles and molecules into simpler, more soluble molecules, such as sugars.
2. Acidogenesis: a first group of bacteria comes into play, transforming the soluble organic molecules into compounds that will be used in the next phase. In this process, certain compounds are also generated that cannot be metabolised by the bacteria that will generate the methane, and any remaining oxygen is eliminated.
3. Acetogenesis: here, a series of microorganisms use whatever that cannot be used by methane-producing bacteria and transform it into acids, carbon dioxide and hydrogen (which will also become part of the final mixture in small quantities).
4. Methanogenesis: A group of bacteria, called methanogens, completes the decomposition process and produces methane. Depending on the organic material that decomposes, this gas will account for up to 70% of the final biogas mixture. A fertilising liquid called biol is produced as a by-product.
   

This process is always repeated in the so-called biodigesters, natural or artificial systems that take harness the digestion of bacteria, in the absence of oxygen, to transform organic waste into biogas and fertiliser. Low-cost home biodigesters, such as those in the Bolivian highlands, have become an increasingly used alternative in Latin America to strengthen the energy self-sufficiency of many households.

This same concept of biodigestion is used in industrial biogas plants, developed to extract energy from organic waste, such as that which accumulates in sewage treatment plants or urban landfills.

A new group of bacteria key in producing biogas

An international team of scientists has announced a finding that could play a major role in boosting renewable energy. It is a new taxonomic order of bacteria specialised in the process of decomposing organic matter, which would therefore make them key to the generation of biogas.

The discovery, dubbed Darwinbacterials, was made possible by taking 80 samples of decomposing organic matter from 45 biogas production plants in different countries such as Germany, Austria and the Netherlands. It has been possible to corroborate the abundant presence of these microorganisms in all the samples collected, despite their being taken from different countries, and to identify this as a microbial group that until now did not appear in the reference databases.

The finding is important, as biogas is increasingly used in different industries due to its high energy value and its great utility as a biofuel.

Looking to the future

This discovery is especially compelling since this gas is a 100% renewable resource that has an energy potential similar to that of natural gas. Not only does it reduce carbon dioxide emissions, one of Europe's main targets for the coming years, but it is also a sustainable way of treating waste and helps boost the circular economy.

Starting in 2024, all EU member countries will have to separately collect organic waste, which can be used for the sustainable production of biogas.

According to the European Biogas Association, this resource has the potential to revolutionise our energy system and lay the foundations for the society, agriculture and water management of the future. As stated by the European Commission, "biogas and biomethane from industry could save up to 35 bcm of natural gas by 2030".

In our country, the Biogas Roadmap has set the course, which “aims to identify the challenges and opportunities for the full-scale development of biogas in Spain”. This document states that we have "the opportunity to take advantage of the great potential available for the production of biogas from the agricultural sector, the agri-food sector and waste management, leveraging the scale of our agricultural and food industry and facilitating the efficient management of municipal waste".

The text also mentions other positive and cross-cutting impacts of biogas, especially in the face of the demographic challenge phenomenon of the depopulation of rural Spain. Thanks to offshore power generation, it is "possible to contribute to combating rural depopulation, generating synergies with the reactivation needs of areas undergoing a process of fair transition".

Green energy in your day-to-day life

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