A Natural Reactor That Combines Microbial Communities Significantly Improves The Quality Of Water Treated In Small Wastewater Treatment Plants

Researchers from the BETA Technology Center of 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 biofilm and plankton-based reactor (BPR) that significantly improves the quality of water treated 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 such as Escherichia coli, two of the main pollutants affecting rivers receiving urban wastewater.

The research is part of the new European Directive on urban wastewater treatment, in force since November 2024. This regulation represents a major change, since by 2025 it not only strengthens the quality standards for large wastewater treatment plants, but also extends the obligation to apply more efficient treatments to small municipalities. These localities, which until now were exempt from most of the requirements, will have to adapt to new demands in terms of reducing nutrients and pollutants. The challenge is considerable, especially in the economic and technical field, but it also represents an opportunity to opt for more sustainable and accessible solutions, such as those based on nature, which allow for improved purification without 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, purifying water without the need to resort to very expensive or energy-intensive technologies," explains Lorenzo Proia, a researcher at the BETA Technology Center and co-author of the work. "It is a sustainable and adaptable alternative, designed especially for smaller treatment plants, which tend to have more difficulty complying with regulations or investing a lot of money in advanced treatments," adds Proia.

"Our results show that microbial communities can significantly reduce nutrients and fecal bacteria in wastewater. This advance offers a solid scientific basis for relying on nature-based solutions and applying them within the framework of the new European regulations," says Lluís Bertrans-Tubau, a researcher at the BETA Technology Center and first author of the article.

In addition, the team has analyzed the system's capacity to eliminate emerging pollutants, such as pharmaceuticals or compounds used in everyday life. Although the results were variable, new optimization opportunities are opened for future versions of the reactor.

According to José L. Balcázar, researcher at ICRA-CERCA and co-author of the study, "the most relevant thing about this approach is that it not only improves water quality, but also helps us understand how microbial communities participate in purification. 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 had 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 commit to nature-based solutions to guarantee the sustainability and water security of our communities, especially in Mediterranean territories, where water scarcity and the vulnerability of ecosystems make innovation in purification even more urgent.