Extreme drought events are expected to become increasingly frequent and widespread across Europe in the coming years because of climate change, according to projections from the Intergovernmental Panel on Climate Change (IPCC).
Droughts cause a significant reduction in water availability, particularly affecting low-flow streams in the Mediterranean region. These ecosystems are susceptible to climate change and are further impacted by various forms of human pressure.
Many of these streams, especially in urbanized areas, continue to flow thanks to discharges from wastewater treatment plants. While these effluents might appear beneficial in maintaining flow and supporting aquatic life, they can also become sources of pollution, negatively affecting water quality and ecosystem health.
Wastewater treatment in small populations
Under the revised EU Urban Wastewater Treatment Directive (2025), all urban areas with more than 1.000 Population Equivalent (PE) will be required to implement secondary treatment by 2035, and nutrient removal (tertiary treatment) in sensitive areas by 2045. Despite this important regulatory advancement, many small wastewater treatment plants still lack sufficient control measures, which contributes to the degradation of stream ecosystems and increases ecological risks to both aquatic and adjacent habitats.
This pollution may stem from excessive nutrient loads—primarily nitrogen and phosphorus—leading to eutrophication, as well as the presence of pharmaceuticals, personal care products, and the emergence of antibiotic-resistant bacteria, a growing concern that remains under-researched.
A need for sustainable alternatives
In response to these challenges, new wastewater treatment approaches that are both sustainable and easy to implement will be essential in the coming years. The Applied Ecology and Global Change Group at the BETA Technological Centre, from the University of Vic – Central University of Catalonia, is developing a Nature-Based Solution for wastewater treatment using aquatic microorganisms and plants.
Nature-Based Solutions (NBS)
Nature-based solutions are defined as the sustainable use of natural features and processes to tackle environmental challenges from a socio-economic perspective, benefiting both people and ecosystems.
In the context of water treatment, the most common NBS include natural bioreactors and constructed wetlands, which are designed to replicate simplified biological communities. These systems utilize microorganisms and plants found in natural aquatic ecosystems, adapted to deliver valuable ecosystem services.
Organisms in these naturalized systems can uptake nutrients for growth and absorb, accumulate, or degrade a variety of pollutants, including pharmaceuticals, antibiotics, and pesticides.
Our research focuses on an NBS approach that employs planktonic and benthic microbial communities capable of assimilating nutrients, like those found in natural streams and rivers. This mimics the self-purification capacity naturally occurring in fluvial ecosystems. These microbial communities, or biofilms, are primarily composed of green algae, cyanobacteria, diatoms, and bacteria.
This type of treatment could significantly reduce the economic and energy costs associated with conventional large-scale wastewater treatment plants. Preliminary results suggest that such nature-based technologies could effectively reduce nutrient concentrations, emerging pollutants, and even certain antibiotic resistance genes in receiving waters like small streams.
Although widespread implementation may take time, this research represents a critical first step in offering public authorities practical alternatives for improving wastewater management in small municipalities and reducing the environmental impact of treatment plant discharges.
In addition, these solutions could help sustain water flow in ecosystems increasingly affected by climate change.
By doing so, a single nature-based solution has the potential to address two major challenges simultaneously: the effects of climate change and anthropogenic pressure on rivers and streams.
This article has been adapted from the original Spanish version: Microorganismos y plantas, las nuevas tecnologías de depuración de aguas”, published on October 9, 2023, in The Conversation by Lluís Bertrans Tubau.
