One characteristic of Mediterranean rivers is their seasonality, which is becoming more pronounced due to climate change. Many rivers and streams are impacted by effluents from wastewater treatment plants (WWTPs) that, in some cases, especially in streams and small rivers, may be the only water flow during dry season, supporting life that otherwise wouldn't exist. Unfortunately, WWTP treatment is insufficient to remove many chemical and biological compounds that can be harmful to the environment, including microplastics, pharmaceuticals, or PFAS, which have been shown to be detrimental to aquatic ecosystems.

As part of the LIFE BIODAPH2O project, the chemical and ecological quality of the Onyar River, as it passes through the towns of Quart and Girona, has been monitored for a year prior to the implementation of the treatment system that the project will evaluate, to establish the baseline conditions of the river. The results have shown a certain deterioration in water quality after the Quart WWTP. The presence of microplastics or perfluorinated compounds, as well as pharmaceuticals or antibiotic resistance genes, has been identified at the WWTP's outlet.

University of Girona researcher Manuela Hidalgo comments that they have detected perfluorinated compounds such as PFBS or PFOA at the WWTP outlet. These substances are present in many everyday products like non-stick coatings in kitchenware, waterproof clothing, or fast-food packaging. Although detected at very low concentrations, they are present in the river, especially in areas closest to the WWTP discharge point. Meanwhile, researcher Víctor Matamoros from IDAEA-CSIC mentions that antibiotics and antibiotic resistance genes, which increase in the river due to the discharge of treated wastewater, make the river a reservoir of antimicrobial resistance genes with implications for human health. Furthermore, suspended particles in the river water increase, overall worsening water quality, as noted by Jordi Colomer from the University of Girona.

The deterioration in the river's chemical quality consequently affects its ecological quality, comments Julio López-Doval from the BETA-Vic technology Center. These impacts are manifested by a decrease in the diversity of aquatic organisms, such as insect larvae, other small invertebrates, and algae groups. An increase in pollution-resistant organisms is observed, taking advantage of these impacts, leading to the disappearance of organisms indicative of cleaner waters that cannot cope with the presence of pollution.

In this regard, University of Girona professor and coordinator of the LIFE BIODAPH2O project, Victòria Salvadó, explains that to minimize these impacts still observed in Mediterranean rivers and streams adjacent to WWTPs, it is necessary to implement additional treatments that ensure much higher quality thresholds in the water discharged into rivers. The BIODAPH2O project is evaluating a tertiary or refining treatment technology for the WWTP outlet in Quart to improve the chemical and ecological quality of the Onyar River as it passes through Girona. This technology (BIODAPH) is based on the filtering capacity of Daphnia. The project's idea is to extend this technology to other Mediterranean areas with similar conditions and to use this water for agriculture, generating a local water source. The BIODAPH system has also been implemented at the Antissa WWTP on the island of Lesbos (Greece) and will produce reclaimed water for irrigating a 7,000 m2 adjacent plot.

The LIFE BIODAPH2O project (LIFE21-ENV-CA-BIODAPH2O) is funded by the European Commission's LIFE program, and the consortium comprises the University of Girona (coordinators), Sorigué, IDAEA-CSIC, the BETA Technological Center, and the Catalan Water Partnership (CWP) as Catalan partners, and MINAVRA Techniki and the National Technical University of Athens (NTUA) as Greek partners.