Nature-based solutions for antibiotics and antimicrobial resistance removal in tertiary wastewater treatment: Microbiological composition and risk assessment

This field-scale study evaluates the seasonal effectiveness of employing nature-based solutions (NBSs), particularly surface flow and horizontal subsurface flow constructed wetland configurations, as tertiary treatment technologies for the removal of antibiotics (ABs) and antibiotic resistance genes (ARGs) compared to a conventional treatment involving UV and chlorination. Out of the 21 monitored ABs, 13 were detected in the influent of three tertiary wastewater treatments, with concentrations ranging from 2 to 1218 ng·L-1. The ARGs sul1 and dfrA1 exhibited concentrations ranging from 1 × 105 to 9 × 106 copies/100 mL. NBSs were better at reducing ABs (average 69 to 88 %) and ARGs (2-3 log units) compared to the conventional tertiary system (average 36 to 39 % and no removal to 2 log units) in both seasons. Taxonomic compositions in influent water samples shifted from wastewater-impacted communities (Actinomycetota and Firmicutes) to a combination of plant rhizosphere-associated and river communities in NBS effluents (Alphaproteobacteria). In contrast, the conventional technology showed no substantial differences in community composition. Moreover, NBSs substantially reduced the ecotoxicological risk assessment (cumulative RQs). Furthermore, NBSs reduced the ecotoxicological risk (cumulative RQs) by an average of over 70 % across seasons, whereas the benchmark technology only achieved a 6 % reduction. In conclusion, NBSs present a robust alternative for minimizing the discharge of ABs and ARGs into surface water bodies.