Biogas and biomethane: key players in the circular economy and the energy transition

“Biogas and biomethane stand out within the bio circularity ecosystem for their ability to offer immediate and viable solutions in the ecological transition.”

Margarita de Gregorio, CEO of Biocirc.

One of the fundamental aspects in the fight against climate change is the economy. Currently, the linear economy, based on the ‘extract, produce, consume and dispose’ model, contributes significantly to the environmental crisis by prioritising economic profit and ignoring sustainability. This way of acting leads to a depletion of natural resources, the generation of large amounts of waste and the emission of greenhouse gases.

It is therefore crucial to move towards what is known as the ‘circular economy’. This new economic system promotes the management and recovery of waste to keep it in the production cycle for as long as possible. This helps to reduce both the consumption of raw materials, and the amount of waste generated.

The part of the circular economy that addresses the production cycle of those sectors whose raw materials are of biological origin is known as bio circularity. This approach makes it possible to replace raw materials of fossil origin with others of renewable origin, while at the same time reusing organic waste, contributing to the decarbonisation of multiple sectors and to a more sustainable management of waste.

In this context, biogas and biomethane play crucial roles thanks to their ability to regenerate natural systems and contribute to the energy transition. But first things first…

What is biogas and biomethane?

Biogas is a renewable, carbon-neutral gas produced from the anaerobic digestion of organic matter, i.e. from the biodegradation of organic waste in the absence of oxygen. Thus, during this process, which takes place in an airtight tank or digester, the carbohydrates, proteins and lipids present in the waste are broken down by a series of bacteria, releasing a mixture of gases known as biogas. In addition, digestate, a biosolid with high fertiliser capacity, is also obtained as a by-product.

The composition of biogas varies depending on the waste used as raw material or substrate, although it is usually between 50-75% methane (CH₄) and 25-45% carbon dioxide (CO₂), with small amounts of other gases such as hydrogen sulphide (H₂S), ammonia (NH₃), volatile organic compounds (VOC) and water vapour.

Of the aforementioned, the methane concentration is the most relevant factor, as it determines the calorific value of the fuel. 1 m³ of biogas with a composition of 50% CH₄ would produce 5 kWh of energy, replacing 0.50 m³ of natural gas; whereas, if the methane composition is raised to 65%, the same cubic metre of biogas would produce 6.40 kWh of energy, replacing 0.65 m³ of natural gas. [These calculations are based on the lower calorific value of natural gas (10.83 kWh/m³)].

On the other hand, before being used as energy, biogas must undergo a process to remove impurities that can cause damage to the installations and reduce the efficiency of the system. H₂S, for example, is highly corrosive and can damage motors, turbines and other equipment if it is not removed adequately. In addition, water vapour reduces the calorific value of the biogas, which is why it is essential to separate it.

After this process, biogas is suitable for use as a fuel in the production of heat in gas boilers or in the generation of electricity through combustion engines, among others.

However, to broaden its applications, biogas can undergo an additional process, known as ‘upgrading’, for the production of biomethane. This process involves the almost total elimination of CO₂ and other residual compounds, raising the methane concentration to more than 95%. The result is a renewable gas with energy-characteristics comparable to fossil natural gas.

The advantage of biomethane over biogas lies in its higher calorific value and its ability to replace natural gas, thanks to its high methane content. This allows biomethane to be injected directly into the existing gas grid, extending its use to sectors such as transport, industry and residential. Its integration into existing infrastructure makes it an immediate decarbonisation solution, especially compared to other renewable gases, which require the development of specific infrastructures. Moreover, if biogenic CO₂ capture is carried out during its production, biomethane can achieve negative carbon emissions.

Opportunities in the valorisation of organic waste

The dual benefits of biogas and biomethane – as a renewable energy source and a climate mitigation tool – are sufficient to take them into account in the transition to a sustainable, low-carbon energy system. But their use has advantages that go far beyond the simple production of energy, as the production of these biofuels is also emerging as an innovative and sustainable solution for the valuation of organic waste produced by various economic sectors.

Currently, part of this waste is managed inefficiently and it often ends up polluting soil, water and the atmosphere itself, which has a high environmental impact. In this context, anaerobic digestion can play a key role in managing waste such as the following:

• Livestock sector: Livestock waste, such as manure, slurry, animal bedding and cleaning water, can lead to the incorporation of heavy metals into the soil, the pollution of water by excess nitrates or the emission of ammonia into the atmosphere if not properly managed.
• Agricultural sector: Agricultural residues, including pruning, wood and herbaceous waste, are often inefficiently managed through indiscriminate burning or abandonment, contributing to environmental degradation, fires and the spread of pests.
• Food sector: Slaughterhouse rejects, waste from the fishing industry, organic waste and liquid by-products from the dairy industry, or fruit or vegetable scraps that are not reused can end up rotting in landfills, where they emit methane, a gas with a warming potential 21 times greater than CO₂.
• Municipal Solid Waste (MSW): The organic fraction of municipal solid waste (MSW), such as food waste or domestic pruning, can be biodegraded and reused to produce energy or natural fertilisers. This process also contributes to achieving the recycling targets set out in Law 7/2022 on Waste and Contaminated Soils, which allows further progress towards a circular economy by reducing municipal waste.
• Wastewater Treatment Plants (WWTP): Sludge generated in wastewater treatment represents a costly challenge for WWTPs, as its management can account for up to 50% of operational costs. Anaerobic digestion can reduce the volume of sludge and generate biogas, turning a problematic waste into a renewable source of energy.

In other words, biogas and biomethane stand out not only as renewable energy sources and tools for decarbonisation, but also for their ability to reduce dependence on fossil fuels, bringing greater flexibility to the energy system.

Their ability to decarbonise sectors that are difficult to electrify is particularly valuable in the transition to a cleaner energy model.

In addition, anaerobic digestion technology is already well established, and the necessary infrastructure is available, making biogas and biomethane an immediate solution.

A crucial added value of these sources is their contribution to the circular economy, since, as we have seen, they allow the revalorisation of organic waste generated by various sectors. Not only do they significantly reduce waste, but they also create new opportunities in sustainable and circular value chains, especially on a small scale and in rural environments. This approach favours the dynamisation of these areas, while contributing to the fulfilment of the objectives of the bioeconomy in Spain, promoting a more balanced and sustainable model of economic development.

Picture 1. Biogas value chain

Biogas and Biomethane Genesal Energy gensets

Genesal Energy is fully aware of the enormous potential of renewable gases and the importance of the circular economy. We participate in projects that promote the valorisation of waste to transform it into valuable resources such as biofuels. These gases can be used on gas power gensets, taking a further step towards a sustainable energy model by not only using a renewable source instead of conventional fossil diesel, but also a source generated from the reuse of waste that would otherwise end up representing an environmental problem.

Hand in hand with FACSA, SMALLOPS, AIMEN and UVA, we are part of the ENEDAR project – ‘Improving the energy efficiency and sustainability of wastewater treatment plants through the valorisation of WWTP sludge’, financed by the Ministry of Science, Innovation and Universities and the European funds NextGeneration UE/PRTR.

Genesal Energy is here responsible for designing and validating the operation of a generator set powered by fuels from the anaerobic digestion of sewage sludge from a pilot plant; reaffirming our commitment to the energy transition and the creation of immediate and practical solutions for a sustainable future.