Removal of iron, chromium and lead from waste water by horizontal subsurface flow constructed wetlands

Background Two pilot scale horizontal subsurface flow constructed wetlands (HSFCWs), with a planted area of 15 m2 each, were constructed in Puglia, Italy, and planted with hydrophytes (Phragmites australis and Typha latifolia), while a similar field of equal size was used as a control. The primary aim of the present work was to assess the removal of three heavy metals from waste water, in relation to the evapotranspiration, using HSFCWs. Results Residence time distributions in both planted HSFCWs indicated that the Typha field had porosity of 0.16 and exhibited more ideal plug flow behavior (Pe = 29.7), compared with the Phragmites field (Pe = 26.7), which had similar porosity. The measured hydraulic residence times in the planted fields were 35.8 and 36.7 h, for Typha and Phragmites, respectively, at waste water flow rates of 1 m3 d−1 (corresponding to hydraulic loading rate of 66.7 mm d−1). Heavy metals concentrations at the inlet were 2 mg/L, for each heavy metal, while at the outlet of the fields were Cr = 0.23 mg L−1, Pb = 0.21 mg L−1 and Fe = 0.18 mg L−1 in the Phragmites field, and the removal rates were 87, 88 and 92% of Cr, Pb and Fe, respectively. The Typha field showed a similar behavior with concentrations equal to Cr = 0.19 mg L−1, Pb = 0.23 mg L−1 and Fe = 0.16 mg L−1 and removal percentages of 90, 87, and 95% of Cr, Pb and Fe, respectively. The control field showed metal removals slightly lower (86, 78 and 88% for Cr, Pb and Fe, respectively). Conclusions HSFCWs are appropriate for removing heavy metals from waste water. Evapotranspiration may significantly reduce the amount of discharged flow and may influence the removal rate of heavy metals.