Environmental performance of constructed wetland planted with monocultures and polycultures for wastewater treatment

The effects of culture systems and seasonality on the environmental impact of constructed wetlands (CWs) remain understudied. This study aims to quantify the environmental impact of common and ornamental plants in a pilot-scale horizontal subsurface flow (HSSF) CW planted with monocultures and a polyculture. Eight scenarios were evaluated, differentiated by plant type, culture system, and season (warm season, cold season). Environmental performance was evaluated using the life cycle assessment (LCA) methodology. The environmental impact index (ƐP), based on eutrophication reduction (kgP removed), and net environmental benefit (NEB) indicators were also calculated. The results showed that a CW planted with polycultures reduced FE by 5–17% compared to those planted in monocultures. However, the polyculture had the highest environmental impact in the GW category, up to 1.5–9 times higher than that of monocultures. Furthermore, there was better performance in the cold season in all scenarios. Specifically, NEB showed an environmental benefit for freshwater eutrophication and a negative benefit for global warming. The ƐP indicator was inversely proportional to the elimination of phosphorus, with the polyculture CW reaching the highest values of 3399 kgCO2eq/kgP removed in the warm season. The assessment of environmental impact patterns could support the development of strategies for better environmental performance of CWs, with polycultures used as an alternative wastewater treatment.