Metal removal from leachate using vertical wetlands

SANCHEZ, G. C; HADAD, H. R; NOCETTI, E; MAINE, M. A; CAMPAGNOLI, M; CAMAÑO SILVESTRINI, N. E

Valencia

Conferencia; IWA Specialist Conference on Wetland System for Water Pollution Control. Internation Water Association; 2018

Landfill leachate contains a wide range of contaminants in concentrations that vary along time. Leachate is usually composed of high concentrations of organic matter and ammonia and low concentrations of toxic pollutants, such as heavy metals. Vertical flow constructed wetlands (VFWs) are commonly studied for leachate treatment focusing on ammonium removal. There is a growing interest in removing metals from leachate through VFWs. Cr(III), Ni and Zn are the main metals contained in the leachate studied. The aim of this work was to evaluate Cr(III), Ni and Zn removal from a real diluted landfill leachate using mesocosms-scale VFWs with recirculation. VFWs were filled with coarse sand and light expanded clay aggregates and were planted with Typha domingensis or Canna indica. VFWs were disposed outdoors under a semi-transparent plastic roof. The acclimatization period and experiment lasted 4 months. As metal concentrations in leachates are variable over time, two metal concentrations were chosen to be studied: 0.2 mg/L Cr + 0.2 mg/L Ni + 0.2 mg/L Zn, and 1.0 mg/L Cr + 1.0 mg/L Ni + 1.0 mg/L Zn. To reach these concentrations, metal solutions were added to the diluted real leachate. The effluent was dumped and recirculated daily. Conductivity, pH, color, COD, Ammonium, Nitrate, Nitrite, Cr, Ni and Zn concentrations were determined in the leachate before and after treatments. Metals were determined in macrophyte tissues at the beginning and the end of the experiment. Chemical analyses were performed following APHA (2012). Metals were determined by absorption atomic spectrometry. VFWs reduced the leachate volume by evapotranspiration and removed organic matter, color and ammonium. Removal efficiencies of Cr, Ni, and Zn at the two concentrations studied for T. domingensis/C. indica were: 43/36, 24/25, 39/37 % for Cr, Ni, and Zn at 0.2 mg/L and 68/62, 60/49, 56/45 % for Cr, Ni, and Zn at 1.0 mg/L, respectively. Recirculation enhances removal efficiencies significantly (60/54, 49/47, 61/47 % for for Cr, Ni, and Zn at 0.2 mg/L and 80/71, 76/62, 73/59 % for Cr, Ni, and Zn at 1.0 mg/L, respectively). Removal efficiencies were higher at high metal concentrations. Both studied macrophytes tolerated leachate and grew vigorously. VFWs planted with T. domingensis presented higher metal removal efficiencies than those planted with C. indica. Metal concentrations in aerial tissues of macrophytes did not increase significantly. However, plant biomass and metal concentrations in roots increased significantly after experiment. Metal uptake and tissue bioaccumulation kinetics are significantly faster than that of nutrients. VFWs proved to be efficient in Cr(III), Ni and Zn removal from leachate.. Further studies are needed to evaluate Cr(III), Ni and Zn retention mechanisms within a VFW.