Researchers from the BETA Technology Center at the University of Vic – Central University of Catalonia (UVic-UCC), the University of Girona (UdG), and the Catalan Institute for Water Research (ICRA-CERCA) have developed a reactor based on biofilms and plankton (BPR, for its acronym in English) that significantly improves the quality of treated water in small-scale wastewater treatment plants.

The study, recently published in the Journal of Environmental Management, shows that this nature-inspired system can significantly reduce nutrients such as nitrogen and fecal bacteria like Escherichia coli, two of the main pollutants affecting rivers that receive urban wastewater.

The research is framed within the new European Directive on Urban Wastewater Treatment, in force since November 2024. This regulation represents a major shift, since by 2025 it not only reinforces quality standards for large wastewater treatment plants but also extends the obligation to implement more efficient treatments to small municipalities. These localities, which until now were exempt from most requirements, will have to adapt to new demands regarding nutrient and pollutant reduction. The challenge is considerable, especially from an economic and technical perspective, but it also represents an opportunity to adopt more sustainable and accessible solutions, such as nature-based ones, that improve treatment without sharply increasing energy or infrastructure costs.

A sustainable and adaptable alternative

“The reactor combines microbial communities that act in a similar way to what happens in natural aquatic ecosystems, treating water without the need to resort to highly expensive or energy-intensive technologies,” explains Lorenzo Proia, researcher at the BETA Technology Center and co-author of the study. “It is a sustainable and adaptable alternative, designed especially for smaller treatment plants, which usually face greater difficulties in complying with regulations or investing large amounts of money in advanced treatments.”
“Our results show that microbial communities can significantly reduce nutrients and fecal bacteria in wastewater. This advance provides a solid scientific basis for trusting nature-based solutions and applying them within the framework of the new European regulation,” states Lluís Bertrans-Tubau, researcher at the BETA Technology Center and first author of the paper.

In addition, the team analyzed the system’s capacity to remove emerging contaminants, such as pharmaceuticals or everyday-use compounds. Although results were variable, new opportunities for optimization arise for future reactor versions. According to José L. Balcázar, researcher at ICRA-CERCA and co-author of the study, “the most relevant aspect of this approach is that it not only improves water quality but also helps us understand how microbial communities participate in treatment. This opens the door to more resilient technologies in the face of climate change and emerging pollution.”

The project was carried out in a pilot plant located in Quart (Girona) and involved a multidisciplinary team of chemists, microbiologists, ecologists, and water management specialists.

In a context of increasing pressure on water resources, this work reinforces the need to invest in nature-based solutions to ensure the sustainability and water security of our communities, especially in Mediterranean regions where water scarcity and ecosystem vulnerability make innovation in treatment even more urgent.