Biomethane is a gas obtained from biogas. The European Union wants to promote its production to offset fossil fuel consumption since biogas is renewable.
However, biogas has a small drawback: when producing biogas, a co-product called digestate is generated, which has complicated management strategies.
Different alternatives are currently being studied to valorize digestate while minimizing pollution. The goal is not only to eliminate it but also to turn it into a useful product.
A group of researchers has discovered that digestate helps decontaminate water, creating a win-win situation: digestates are no longer an environmental problem and can be given a sustainable economic use.
Digestates can be transformed into biochar through a process called hydrothermal carbonization. Biochar can decontaminate water by removing organic contaminants.
This is the gist of the UPGRES project, carried out by a team of scientists from the Chemical and Environmental Engineering Group at Rey Juan Carlos University (URJC), in collaboration with Repsol and INGELIA.
Juan Antonio Melero, a Professor of Chemical Engineering at Rey Juan Carlos University, is the principal investigator of the UPGRES project. "A lot of this digestate could end up in landfills, which is not sustainable. This is where UPGRES comes in, offering new ways of valorizing digestate," says Juan Antonio.
The Repower EU project, promoted by the European Union, aims to boost biomethane generation, increasing production from the current 20 billion m3 to 35 billion by 2030, and 167 billion by 2050. This would cover 60% of the EU's natural gas demand but would also generate 1.7 billion tonnes of digestate compared to the current 180 million tonnes.
While digestate can also be used as a fertilizer, it has low agronomic value, and its use is limited depending on its origin.
Digestate is transformed into biochar (hydrochar) through hydrothermal carbonization, which is carried out at temperatures between 180 and 250 ºC, producing a bio-based carbon. What nature does by fossilizing organic waste and transforming it into fossil charcoal, these researchers achieve in four hours.
In the UPGRES project, they manage to degrade pollutants from wastewater or industrial effluents using the generated biochar.
“Currently, we are in the basic research stage. The next step would be for companies to scale it up to a pilot plant, where digestates would be treated in larger reactors," explains Isabel Pariente, a professor in the area of Chemical Engineering at Rey Juan Carlos University and head of the water treatment line.
"This process can be used for process waters with a high concentration of organic matter at a temperature of 200 ºC and 50 bars of pressure. Its profitability would need to be studied," she adds.
UPGRES is a project funded by the State Research Agency for strategic R&D&i lines. IMDEA Energía, Repsol, Ingelia—a Valencian company dedicated to the hydrothermal carbonization of biological waste—and Rey Juan Carlos University are participating in it.
UPGRES project began in November 2021 and will end in November 2024.
