Comparative nutrient removal efficiency of three Cyperus species in vertical flow type of constructed wetlands, Sebeta, Ethiopia

Abstract

River water pollution is increasingly widespread in and around Addis Ababa and can lead to problems with users if not properly treated. Constructed wetlands are a promising solution and are being used by several countries. In this study three Cyperus species (Cyperus alternifolius, Cyperus papyrus and Cyperus usitatus) and substrate only were investigated for their removal efficiencies of TSS, BOD, NH₄-N, NO₃-N, TP and total coliforms (TC) from polluted river water in a free vertical surface flow (VSSF) wetland system.  The maximum NO₃-N, BOD, TSS, NH₄-N and TP removal efficiency by C. cyperus were 95.5%, 78.5%, 76.1%, 68.2% and 66%, respectively. C. alternifolius was superior in removal efficiency compared with other treatments but C. papyrus was the highest in TC removal (92.2%). Treatment with substrate only has the lowest removal efficiency. No significant differences were observed in the removal efficiency of Cyperus species and substrate only among 3, 5 and 7 days of hydraulic retention time. Apart from nutrient removal, constructed wetland cells purified and improved the colour of the wastewater which is an added advantage to change the appearance of polluted rivers. C. alternifolius and C. papyrus have a higher nutrients, TSS and BOD removal efficiencies and can be considered from a treatment perspective in constructed wetland. Further research is required to select multipurpose wetland plants with high wastewater removal efficiency, and potential as livestock feed which was not determined in this experiment.