Hybrid constructed wetlands for the treatment of urban wastewaters: Increased nutrient removal and landscape potential

The universalization and decentralization of wastewater treatment is one of the greatest challenges faced in Brazil. In this context, Constructed Wetlands (CWs) may be considered environment friendly and economically viable alternative for geographically remote locations, having fewer financial resources and infrastructure. During the last years, studies have investigated different configurations aiming to increase the capacity of CW to remove nutrients, mainly phosphorus (P) and reinforced its importance in ecological and landscape contexts. Thus, the present study evaluated the performance of a hybrid system combining Floating, Vertical and Horizontal Flow CWs to treat urban wastewaters. A removable adsorbent barrier was developed to improve the removal of P and a polyculture with ornamental plants was used to add landscape potential. The obtained results showed a promising nutrients removal capacity of the hybrid system, with mean removal rates of 94.0% for total P, 93.8% for ammonium nitrogen (N-NH3), 93.8% for total nitrogen (N), 80.0% for dissolved organic carbon (DOC), 84.0% for biochemical oxygen demand (BDO5), 77.0% for chemical oxygen demand (COD) and 99.7% for turbidity. The integrated system kept its ability to remove pollutants during the 11 months of operation (January to December 2019), without substrate saturation, and also maintaining P values within the limits allowed by current Brazilian (CONSEMA Resolution 355/17 (3 mg L-1)) and international legislation (UWTD 91/271/EEC (2 mg L-1)). The landscape benefits were extremely positive mainly due to the flowering of Canna generalis and its greater biomass production. By crossing the biomass data and the accumulation of nutrients in the tissues of the aerial part it was possible to verify that the contribution of the plants in the N removal from the system reached 8.08% while the P decrease attained 17.92% in the horizontal sub-surface flow constructed wetland (HSSFCWs). Therefore, the developed system enabled an efficient removal of nutrients throughout the monitoring period, enhancing the wastewater quality and potentializing its reuse for different purposes.