Comparative Assessment of Wastewater Treatment Technologies for Pollutant Removal in High-Altitude Andean Sites

This study evaluates the pollutant removal efficiency of two decentralized wastewater treatment plants (WWTPs), Acchayacu and Churuguzo, located in the southern Andes of Ecuador. Until 2021, Acchayacu worked with an upflow anaerobic filter (UAF), after which it transitioned to vertical subsurface flow constructed wetlands (VSSF-CW). In contrast, Churuguzo employs surface flow constructed wetlands (SF-CW). Key parameters such as five-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total phosphorus, organic nitrogen, ammonia nitrogen, total solids, fecal coliforms (TTC) and total coliforms (TC) were analyzed from 2015 to 2024, divided into two subperiods to account for the technology change in Acchayacu. Statistical analysis was conducted to determine whether significant differences exist between the treatment efficiencies of these technologies. Results indicate that Churuguzo achieved higher removal efficiency for BOD5, COD, TTC and TC than Acchayacu. Although the transition to VSSF-CW improved Acchayacu performance relative to its previous UAF system, SF-CW demonstrated superior efficiency. This difference is likely attributed to longer hydraulic retention time, lower surface loading rate and vegetation type used. The findings highlight the environmental implications of treatment technology selection in WWTPs, particularly concerning the quality of receiving water bodies and their potential applications.