Decentralized wastewater management using treatment wetlands: Effective removal of antibiotics, resistance genes and organic micropollutants.

Treatment wetlands (TW) are a popular choice for decentralized wastewater treatment, with substantial documentation on their capacity to manage conventionally monitored pollutants. However, most insights into their effectiveness against emerging contaminants come from lab and mesocosm studies with a limited number of compounds, highlighting knowledge gaps in their performance at full scale. This study provides a first long-term, full-scale assessment of TW ability to remove a large number of organic micropollutants (OMPs) and manage antibiotic resistance under real-world conditions. The TW, with Phragmites australis as the plant species, operational for 10 years with a vertical flow bed followed by an aerated bed, serves a Danish village with a 100 population equivalent. We have monitored its performance over 18 consecutive months (each 3 weeks), analysing organic carbon, nitrogen and OMPs (e.g. pharmaceuticals including antibiotics). Moreover, the microbial community structure (abundance and biodiversity) and possible presence of Antibiotic resistance genes (ARGs) in wastewater and reed rhizosphere at different points of the TW were analysed in four seasonal samplings. The findings demonstrated robust nutrient and OMP removal, with slight performance reductions in winter, likely due to plant dormancy and lower temperatures. Due to the small population served by the TW, antibiotics entered the system sporadically but at peak concentrations. The sul1, sul2 genes associated with sulfonamide resistance and intI1 gene were detected in all microbiological samples. The vertical flow bed effectively reduced OMPs (including antibiotics) and ARGs thanks to the removal action of the reed-microbiome system. The TW was a biofilter for targeted emerging contaminants, limiting their transfer in the water cycle and this study uniquely demonstrates that full-scale TWs can achieve high removal efficiencies for both antibiotics and ARGs, offering new insights into their practical application and operation for decentralized wastewater management.