Evaluation of Pilot-Scale Constructed Wetlands with Phragmites karka for Phytoremediation of Municipal Wastewater and Biomass Production in Ethiopia

Abstract

A pilot horizontal subsurface flow constructed wetland (HSSFCW) was constructed, covered with geomembrane, and packed with gravel as substrate. Phragmites karka was planted in one cell and the other cell was left unplanted. The experiment was carried out over a 3-year period at two hydraulic loading rates (HLRs): 0.025 m/d and 0.05 m/d. The aim of the study was to evaluate the phytoremediation and biomass production potential of Phragmites karka for municipal wastewater treatment to remove chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The highest average COD, TN, and TP removal performances attained were 94.1%, 97.3%, and 89.9%, respectively, at HLR of 0.025 m/d, and 90.4%, 86.8%, and 88.5%, respectively, at HLR of 0.05 m/d. COD, TN, and TP removal performances were considerably higher in the planted HSSFCW than in the unplanted (p < 0.05). The study found: a progressive increase in plant density, from 3 ± 1 to 113 ± 43 shoots per m2; an increase in plant height (erect), from 8 to 365 cm; and growth of the running stem of P. karka (stolon) to 16 m after 16 months. The maximum nutrient content and nutrient accumulation of the above-ground biomass of P. karka recorded were 78.7 gN/kg DW and 21.6 gP/kg DW, and 2014.7 gN/m2 and 550.4 gP/m2 throughout the experimental period. The findings from the experiments showed the successful performance of the HSSFCW cell planted with P. karka for the treatment of municipal wastewater. P. karka demonstrated high biomass production and high nutrient removal performance. We conclude that scaling up this pilot HSSFCW has great potential for treating municipal wastewater in Ethiopia and other low-income countries with similar climatic conditions.