The high consumption of pharmaceuticals is a growing problem of wastewater pollution, both urban and industrial. In southern Europe, in particular, the scarcity of water and the high consumption of these drugs aggravate the situation, which conventional purification systems cannot solve 100%.
A nature-based solution, such as constructed wetlands, is emerging as an effective technology for improving water quality and reducing emerging pollutants.
This is revealed by a study by the Institute for Environmental Diagnosis and Water Studies (IDAEA) published in the journal Water Research, which has evaluated the effectiveness of these types of solutions as tertiary wastewater treatment techniques to eliminate antibiotics and antimicrobial resistance genes, comparing the results with those of conventional treatments.
The work, carried out in collaboration with the German Karlsruhe Institute of Technology (KIT) and on a real scale in the Besós River and in the Can Cabanyes wetland (Barcelona) has revealed that surface flow constructed wetlands eliminate an average of 88% of the antibiotics present in wastewater, while horizontal subsurface flow wetlands reach 69%. Both percentages significantly exceed the results offered by conventional technologies that combine sand filtration, disinfection by ultraviolet light and chlorination, which eliminate between 36 and 39%.
As for antibiotic resistance genes, although conventional purification systems already offered a 99% reduction, wetlands have demonstrated the ability to eliminate up to 99.9%, both in summer and winter.
Before passing through the wetlands, 13 of the 22 analysed were detected in all water samples. They are used to treat infections of the upper respiratory tract, urinary tract or reproductive organs, which coincides “with the data on both the extensive use of these drugs and their low elimination in wastewater treatment plants,” says Edward Jair Pastor, a researcher in training at IDAEA, a centre of the CSIC (Spanish National Research Council) branch in Catalonia.
The work of wetlands
“Constructed wetlands are purification systems that degrade the materials present in wastewater through physical, chemical and biological processes that occur in nature,” explains Victor Matamoros, researcher at IDAEA and lead author of the study. “Wetland plants release oxygen and other chemical substances through their roots, thus creating an environment conducive to the presence of specific microorganisms that accelerate the degradation of pollutants,” explains the researcher.
It was already known that these systems are capable of eliminating these remains of medicines, as well as nutrients and organic matter. “Now we have also shown that they produce less impact on the aquatic system,” Matamoros points out.
The study also showed that these natural solutions also reduce the risk of toxicological impact on ecosystems by an average of 70%, compared to the meager 6% achieved by conventional technologies. “These findings reveal a promising advance in the protection of the environment and public health,” says Victor Matamoros.
This research has also highlighted that the use of these wetlands positively changes the water profile, increasing its quality, as it generates a microbiota more aligned with natural ecosystems, thus reducing the impact on rivers and riverbanks.
The fact that the wetlands in which the study was carried out, Montcada i Reixac and Can Cabanyes, are already operating, has allowed the study to be carried out on a real scale, not in a laboratory. Therefore, the results support Víctor Matamoros’ statement: “constructed wetlands are presented as a viable alternative for widespread application and aligned with global water quality objectives.”
Of course, these infrastructures also have the handicap of requiring a very large surface area. This would not be a problem if there is land available, for example in the flood zone of a river. In any case, Matamoros adds, we are working on another project, UpWater, in which we are evaluating intensified wetlands, which require a smaller surface area of land and could be installed where there is less availability of it.
For this reason, the research team believes that “wetlands are not only effective, they are essential for future wastewater management strategies. The study paves the way for promoting the use of nature-based solutions as a bridge between existing wastewater treatment plants and the receiving environment, and favours the good condition of surface water bodies.”