Influence of Bed Depth on the Development of Tropical Ornamental Plants in Subsurface Flow Treatment Wetlands for Municipal Wastewater Treatment: A Pilot-Scale Case

The aim of this 2-year study was to evaluate the influence of bed depth (40 and 60 cm) on the development of tropical ornamental species (Alpinia purpurata, Heliconia latispatha and Strelitzia reginae) and on the removal of different contaminants such as chemical oxygen demand (COD), nitrate (N-NO3), ammonium (N-NH4), total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS), total coliforms (TCs) and fecal coliforms (FCs), in horizontal subsurface flow constructed wetlands (HSSF-CWs) for municipal wastewater treatment. The results showed that the depth of 60 cm favored the removal of COD, with removal efficiencies of 94% for the three plant species. The depth of 40 cm was most effective for the removal of N-NH4 (80-90%). Regarding the removal of TN, the removals were similar for the different plants and depths (72-86%). The systems only achieved up to 60% removal of TCs and FCs. The depth of the CWs substrate and its saturation level influenced the development of ornamental vegetation, particularly flower production. For Heliconia latispatha, a bed depth level of 60 cm was more suitable, while for Alpinia purpurata 40 cm was better, and for Strelitzia reginae in both cases there was no flower production. The impact of bed depth on contaminant removal depends on the specific type of contaminant.