By now, we know that the transition to a cleaner energy model is not just an option, but an urgent necessity. In this scenario, biomethane emerges as a star resource , as it allows us to convert what we would normally throw away, such as agricultural waste or sewage sludge, into a versatile and powerful energy source that can easily replace fossil gas.
For those who aren't very familiar with the topic, we're basically talking about a renewable gas that, after undergoing a cleaning process, is virtually identical to natural gas. This is a huge advantage because we can utilize existing pipelines and networks , avoiding the need to build infrastructure from scratch and giving a real boost to sustainability in agriculture and industry.
What exactly is biogas and how is it converted into biomethane?
It all begins with anaerobic digestion, a process where microorganisms work tirelessly to break down organic matter in the absence of oxygen. For these microorganisms to thrive, the fermenter must maintain a stable temperature, typically between 35 and 55 °C , and the contents must be constantly stirred to ensure proper nutrient distribution. The result of this process is biogas, a mixture composed primarily of methane and carbon dioxide, along with traces of hydrogen, nitrogen, and hydrogen sulfide.
However, biogas straight from the digester is not biomethane. To obtain biomethane, we need to carry out a process called upgrading or purification . The goal is to remove impurities, especially CO2, so that the methane content increases to a purity of around 95%. In this way, we obtain a high-quality fuel that can be seamlessly integrated into the existing gas system .
Upgrading technologies: How is the gas cleaned?
There are several ways to separate CO2 from methane, and the choice depends largely on your needs and budget. Some of the most common options are:
- Water wash (PWS): The fact that CO2 dissolves better in water than methane is exploited by washing the gas in a column.
- Pressure separation (PSA): The biogas is passed under pressure through molecular carbon tanks that trap the CO2.
- Cryogenic separation: It consists of cooling and compressing the gas to distill it, making it the ideal option if we want obtain biomethane in liquid state.
- Chemical absorption: Amines are used in a scrubbing column. It is a very safe system because it operates without high pressures and is very efficient.
- Polymeric membranes: The gas passes under pressure through membranes that allow CO2 to pass through more easily than methane.
It is worth noting that chemical absorption and membranes are currently some of the most balanced solutions, offering purification above 96% with fairly low operating costs.
Applications and uses of biomethane
The best thing about this system is that biomethane isn't just for one thing; it's a true energy utility. First, it can be injected directly into the gas network to supply homes and industries, replacing fossil natural gas. Second, it's a fantastic fuel for transportation; the use of CNG (compressed natural gas) is rapidly gaining traction in urban bus fleets and heavy transport , drastically reducing greenhouse gas emissions.
Furthermore, we cannot forget that biogas (before being purified) can be used in cogeneration plants to produce electricity and heat simultaneously . And looking to the future, biomethane is a fundamental raw material for the production of renewable hydrogen , thus closing a completely clean energy cycle.
Social, economic and environmental benefits
Beyond energy, implementing these systems has a positive impact on people. In rural areas, biomethane production drives job creation and boosts the local economy, linking the livestock sector with technological innovation. Furthermore, it promotes a textbook circular economy, as the digestate (the byproduct of the process) is returned to the fields as high-quality organic fertilizer.
From a climate perspective, the benefit is enormous. By capturing methane from waste—a gas with a global warming potential 21 times greater than CO2—we prevent it from reaching the atmosphere. This not only helps us meet the Sustainable Development Goals but also directly contributes to the REPowerEU plan to reduce Europe's energy dependence .
The current situation and the future in Spain
Spain has incredible potential due to its large volume of agricultural and livestock waste. Although we started later than countries like Germany or France, the 2022 Biogas Roadmap has set a clear path. The goal is ambitious: to go from modest production to reaching between 10 and 20 TWh annually by 2030.
To achieve this, tools such as Enagás' Green Link service have been implemented , facilitating the connection of plants to the high-pressure network, along with the creation of a Guarantee of Origin system. Distributed biomethane production models are also being explored , where small farms cooperate by producing biogas locally and sending it to a central purification plant, thus sharing the risks and investment costs.
The integration of Agriculture 4.0 technologies, CO2 liquefaction, and the combination with photovoltaic energy are transforming biomethane plants into sustainable and self-sufficient energy centers . This entire ecosystem allows waste management to cease being an environmental problem and become a strategic asset that protects the climate and guarantees the region's food and energy independence.
