Aerated pilot-scale treatment wetland to remove chemical and fecal pollution contained in combined sewer overflows

Treatment wetlands (TWs) have been proposed as a reliable method for removing pollutants from combined sewer overflow (CSO). However, there is a lack of studies on the performance of aerated TWs in removing micropollutants from CSO. We assessed the role of two pilot-scale TWs, one with gravel top layer and the other with sand top layer, fed with mixed domestic wastewater and stormwater under different operational conditions. Samples were collected over a period of more than one year, and analyses of micropollutant treatment performance were based on their frequency of occurrence or chemical class. Fecal indicator (FI) analyses were conducted after the TWs had been in operation for over one year. In general, the removal efficiency of tyre-related micropollutants was over 70% for 6PPD-quinone and less than 40% for benzothiazole, its derivative aminobenzothiazole and hydroxybenzothiazole, with considerable variability. The removal efficiencies of the pharmaceuticals diclofenac, gabapentin, iomeprol, and irbesartan also varied considerably. Compounds such as DEET, gabapentin and iomeprol, had moderate to low removal efficiencies for both TWs, with median removal rates <50%. Conversely, compounds such as irbesartan had negative removal efficiencies, suggesting desorption. The filters effectively removed particulate metals, although dissolved metals generally passed through without being retained. The FI analysis indicated that disinfection was negligible, with an E. coli reduction <1 log₁₀. The results showed moderate retention of micropollutants in aerated CSO TWs, with no considerable enhancement in removal due to artificial aeration. • 23 compounds were quantified in influent or effluent of CSO TW. • Tire-derived contaminants and diclofenac showed medium to good removal efficiencies. • Irbesartan, carbamazepine, DEET, gabapentin, iopremol and pathogens were not removed. • Aerobic conditions with >7–10 h hydraulic retention time are necessary. • Filtration removed 14 metals bound to suspended solids.