Influence of partial saturation and organic loading on the performance of vertical wetlands for raw wastewater treatment

Vertical flow constructed wetlands (VFCW) are employed in wastewater treatment for the removal of organic matter and nitrification. However, they present limitations regarding total nitrogen (TN) removal, especially when treating raw wastewater. This study aimed to evaluate the performance of traditional VFCW systems (unsaturated) and adapted systems with partial saturation in the removal of carbonaceous organic matter (chemical oxygen demand—COD) and TN from raw domestic wastewater. The VFCWs, filled with coarse gravel, had a surface area of 0.031 m² and were planted with Canna x generalis. Three hydraulic loading rates (HLR) were evaluated, of 40, 70, and 100 mm d⁻¹, with organic loadings of 49, 86, and 123 g COD m⁻² d⁻¹, in two groups: unsaturated wetlands (UNW) and partially saturated wetlands (PSW). Better COD removal was observed in PSW (96, 95, and 93% for HLR of 40, 70, and 100 mm d⁻¹, respectively) compared to UNW (86, 84, and 78% for HLR of 40, 70, and 100 mm d⁻¹, respectively). Similarly, for TN removal, better performance was also observed in PSW (94, 87, and 79% for HLR of 40, 70, and 100 mm d⁻¹, respectively). Thus, PSW filled with coarse gravel enable good performance in the simultaneous removal of COD and TN, with nitrification and denitrification in the same treatment unit. Furthermore, the application of this modality in raw wastewater treatment, without the need for primary treatment units, contributes to increasing the technical and economic attractiveness of this technology.