Hybrid constructed wetlands system with intermittent feeding applied for urban wastewater treatment in South Brazil

Abstract

Hybrid constructed wetlands composed by vertical flow constructed wetland (VFCW) followed by horizontal subsurface flow constructed wetland (HFCW) are a wastewater treatment technology employed worldwide. However, there are few studies of their application in Brazil. Treatment performance is not achieved directly after the start of operation and may change according to external conditions over time. This paper evaluated a VFCW–HFCW hybrid system applied to treat urban wastewater in southern Brazil during the first 70 operational weeks. The system was operated with cycles of rest and feed periods. The results point to the first 10 weeks of operation as a transitioning period, especially for VFCW, after which chemical oxygen demand (COD) (from 77% to 90%) and total suspended solids (TSS) (from 90% to 100%) removal performances stabilized and reached their peak rates. Factors such as rainfall precipitation, macrophytes' adaptation, and time of operation affected pollutants' removal. Regardless of the fluctuations throughout the period, the hybrid system presented resilience by generating excellent average removal rates. It showed a mean removal efficiency of 99% for TSS, 98% for COD, 69% for total nitrogen (TN), 91% for NH4+-N, and 96% for P-PO43−. Moreover, the effluent was always suitable to be discharged into the environment according to Brazilian national and state regulations.