Hydrothermal Valorisation of Wet Residues: From Sludge and Algae to Sustainable Bioproducts
A technology that transforms complex residues into bio-oils and biochar, reducing costs and promoting the circular economy
In sectors such as wastewater treatment, sludge management, or algae cultivation, one of the main challenges is finding an efficient process to valorise wet residues. The high water content in these materials complicates their use, and in many cases, they end up representing a cost rather than an opportunity. Faced with this challenge, the search for technological solutions capable of turning a liability into a resource has become a priority for many companies.
Hydrothermal technology: a solution based on water, temperature, and pressure
Hydrothermal technology emerges as a solid alternative to overcome the challenge of valorising wet residues. The principle is simple: instead of removing the water present in the residues – a process that is usually costly and inefficient – the moisture is used as part of the reaction.
The procedure consists of subjecting the residues to high temperatures (200–350 °C) and elevated pressures inside a reactor. Under these conditions, water facilitates the decomposition of organic matter and transforms it into simpler and more stable molecules, avoiding the use of chemical solvents. During the process, two main products are generated: bio-oils, with great potential as a raw material for sustainable fuels, and biochar, which can be used both for energy purposes and in agricultural applications.
What distinguishes this technology is its ability to work directly with wet materials, such as wastewater sludge or algae, without the need for prior drying.
From waste to resource: the benefits of hydrothermal technology
Hydrothermal technology reduces management costs by transforming a problem into a source of energy or a usable product, while also helping to reduce dependence on fossil resources. In this sense, it naturally fits into circular economy strategies, where efficiency and resource reuse are key to improving both competitiveness and sustainability for companies.
Case study: the European CAPTUS project
A real-world example is the European research project CAPTUS, coordinated by CIRCE, where this technology is used to valorise algae cultivated from captured CO₂. The result of this process is oils that, once transformed, become sustainable fuels. This experience demonstrates that hydrothermal valorisation is not just a laboratory concept, but a viable solution capable of integration into industry and contributing to the decarbonisation goals set in Europe.
Read the original spanish article und find out more about CIRCE here.