Efficiency evaluation of wastewater treatment by three macrophytes using a pilot-constructed wetland system in Ota, Nigeria

Three aquatic macrophytes were used to treat wastewater using a pilot-constructed wetland (CW) system to determine the most efficient plants for removing contaminants from wastewater. The three macrophytes are water hyacinth (<i>Eichhornia crassipes</i>), water lettuce (<i>Pistia stratiotes</i>), and duckweed (<i>Lemna minor</i>). Three 150 L capacity tanks with sand and gravel as substrates were used as the pilot CW for each plant. Upon initial examination, the raw wastewater was not compliant with standard discharge limits. The wastewater samples were collected every 7 days for 3 weeks for treatment. From the findings, at 14 days hydraulic retention time (HRT), <i>E. crassipes</i> and <i>P. stratiotes</i> achieved the highest total phosphorus (TP) and chemical oxygen deman (COD) reductions of 99.3 and 99.4%, respectively. <i>E. crassipes</i> indicated better biological oxygen demand removal efficiency of 91.3%, COD (85.0%), electrical conductivity (90.4%), total dissolved solids (89.7%), and total coliforms (66.0%). Albeit, <i>P. stratiotes</i> indicated better results for total suspended solids (96.2%), TP (7.55%), and <i>E. coli</i> (94.4%), while <i>L. minor</i> was better with 90.8% total nitrogen removal. The overall analysis showed <i>E. crassipes</i> to be more efficient than the three macrophytes. However, the other two plants are replaceable options and large-scale implementation of this project in the community would be a major contributor to actualizing SDG number 6.