Removal of heavy metals in subsurface flow constructed wetlands: Application of effluent recirculation

This study reports four heavy metals, i.e., Zinc (Zn), Chromium (Cr), Nickel (Ni), and Lead (Pb) removal from landfill leachate employing two-hybrid subsurface flow constructed wetland systems; each system included a vertical flow (VF) followed by a horizontal flow (HF) wetland. The wetland systems were packed with organic (coco-peat) or construction (brick, sand) materials and planted with Phragmites australis or Chrysopogon zizanioides (Vetiver). Both systems were operated under without, and with effluent recirculation protocols. Cr, Ni, and Pb concentration were 2–73 mg/kg, 3–12 mg/kg, and 0.00004–27 mg/kg, respectively in Phragmites; 8–34 mg/kg, 3–15 mg/kg, and 0.00004–14 mg/kg, respectively in Vetiver. Organic carbon (C) and iron (Fe) of the coco-peat, brick allowed media-based metals removal in VF wetlands; such accumulation was not quantified in sand-based HF wetlands. Zn, Cr, Ni, Pb removal percentages increased between 75 and 98%, 29 and 41%, 14 and 48%, 23 and 26%, respectively, in VF wetlands during the effluent recirculation period (compared with removal performances of without recirculation phase). Removal percentages were reduced in HF wetlands during the recirculation period. Overall, Zn, Cr, Ni, Pb removal percentages in the two-hybrid wetlands ranged between 20 and 97%, 95 and 99%, 55 and 73%, 69 and 83%, respectively.