Organic Matter and Nutrients Removal in Tropical Constructed Wetlands Using Cyperus ligularis (Cyperaceae) and Echinocloa colona (Poaceae)

Abstract

In tropical countries like Colombia, a large variety of available aquatic plants have yet to be investigated for phytodepuration processes. The aim of this study was to assess the effect of Cyper-us ligularis and Echinocloa colona¸ two local plants of Colombian Caribbean region, on removal of dissolved organic matter (COD) and nutrients (N-NH4 +, N-NO3 − and P-PO4 −3) from domestic wastewater. Experiments were conducted in replicate pilot-scale Horizontal Subsurface Flow Constructed Wetlands (HSSF CWs) (0.66 m2). Four wetland treatment units were installed in parallel. Two were planted with C. ligularis and the other two remained with E. colona. The experimental system was connected to a 0.76-m3 primary sedimentation tank that fed experimental wetland treatment units. Wetlands were filled with granite gravel (~8 mm and 0.4 of porosity). During a period of 4 months, each treatment unit received a continuous loading at the rate of 42 L day−1 and a hydraulic retention time of 2.3 days approximately. Wastewater samples from influent and effluents were collected three times each week in order to monitor temporal/spatial changes in removals efficiencies of COD, N-NH4 +, N-NO3 −, and P-PO4 −3. Results showed that removals of COD, N-NH4 +, and N-NO3 − were not significantly different between treatments (p > 0.05). Nevertheless, P-PO4 −3 removal for E. colona was significantly higher than C. ligularis (p < 0.05), showing that this plant can assimilate important amounts of P. Further investigations must be conducted to evaluate the potential of native aquatic macrophytes for phytodepuration.