Year-round performance of full-scale vertical and horizontal treatment wetlands for domestic wastewater and graywater reuse under temperate rainy conditions in Southern Chile

This study evaluated the performance of three full-scale treatment wetlands (TWs) operating under temperate rainy conditions in southern Chile, treating domestic wastewater (one vertical flow, VF) and graywater (one VF and one horizontal flow, HF). Water quality parameters – temperature, pH, oxidation–reduction potential, electrical conductivity, chemical oxygen demand (COD), total suspended solids (TSS), nitrogen species (NH4+-N, NO3--N, TN), phosphorus species (PO43--P, TP), and Escherichia coli – were monitored in influents and effluents over one year, with data analyzed across cold and warm periods. Effluent quality was further assessed against irrigation reuse standards. Results showed effluent temperatures consistently below 15 °C, along with different pH behavior in each TW. VF TWs exhibited more oxidative conditions than the HF TW, a pattern consistent across wastewater types and periods. All TWs removed TSS, COD, NH4+-N, NO3--N, PO43--P, and TP, achieving removal efficiencies between 20 and 95%, sustaining stable performance year-round, and VF effluents more closely meeting irrigation reuse standards. However, TN and pathogen removal remained limited, highlighting the need for further improvement and research. Overall, these TWs demonstrated a strong potential to produce effluents suitable for agricultural reuse, underscoring their applicability in Chile and other places with similar climatic conditions.