Free water surface constructed wetlands for domestic wastewater treatment: A tropical case study

The performance of three free water surface constructed wetlands in treating domestic wastewater was examined. One unit was planted with Scirpus grossus (L2), one was planted with Typha angustifolia (L3), and the unplanted third (L1) was the control. Biological oxygen demand (BOD5), nitrate (NO3-N), ammonium (NH4-N), total phosphorus (TP), and total suspended solids (TSS) of influent and effluent were regularly measured. The average BOD5 removal efficiencies were 44%, 68%, and 54% for units L1, L2, and L3, respectively. The plant growth was continuously monitored in marked quadrats by measuring the shoot height and other growth parameters. The above-ground biomass of L2 and L3 was harvested 8 months and 11 months after the planting date when the plants reached the maximum shoot height and at the start of inflorescence formation. S. grossus was superior to T. angustifolia, with faster establishment, higher productivity, and higher removal of BOD5. However, the growth of S. grossus was possibly inhibited by continuously high NH4+ concentrations, while T. angustifolia showed tolerance of high NH4+ concentrations.