Metal removal from landfill leachate using a vertical flow and a hybrid wetland

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

Aarhus

Simposio; 8th International Symposium on Wetland Pollutant Dynamics and Control-WETPOL 2019; 2019

Aarhus University

Landfill leachate is usually composed of high concentrations of organic matter and ammonia and low concentrations of toxic pollutants, such as heavy metals. Vertical flow wetlands (VFWs) are commonly used as a first stage for leachate treatment focusing on ammonium removal. In the last years, there is a growing interest in metal removal from leachate using constructed wetlands (CWs). The aim of this workwas to evaluate Cr(III), Ni(II) and Zn(II) removal from a landfill leachate using mesocosms-scale VFWs and a hybrid wetland (HW), composed by a VFW and a free water surface (FWS) wetland. In the first experiment, VFWs with free drainage, filled with coarse sand and light expanded clay aggregates and planted with Typha domingensis or Canna indica were studied. Real leachate was diluted and spiked with metals to reach the following concentrations: 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. The effluent was dumped daily. Leachate samples were takentwice a week during 3 months. Removal efficiencies for VFWs planted with T. domingensis/C. indica were: 43/36, 24/20, 39/32 % 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. VFWs planted with T. domingensis presented higher metal removal efficiencies than those planted with C. indica. To improve metal removal efficiencies, a HW composed by a VFW and a FWSW was studied. Both wetlands were planted with T. domingensis. Real leachate was diluted and spiked with metals to reach the following concentrations: 1.0 mg/L Cr + 1.0 mg/L Ni + 1.0 mg/L Zn and 5 mg/L Cr + 5 mg/L Ni + 5 mg/L Zn. Removal efficiencies for the lowest concentration of metals studied were 82, 55 and 64% for Cr, Ni and Zn, respectively after the VFW. After the FWSW, removals were 98, 90 and 95 % for Cr, Ni and Zn, respectively. In the experiment with concentrations of 5 mg/L of metal, removals of Cr, Ni and Zn were 62, 49, 49%, respectively after the VFW. After the second stage (FWSW), the removals reached 95, 88 and 90 % for Cr, Ni and Zn, respectively. The HW studied was not only highly efficient in metal removal but also in ammonium, TN and COD removal from landfill leachate. Plant biomass and metal concentrations in roots increase significantly at the end of the experiment. It was determined by X-ray microanalysis that Cr, Ni and Zn were accumulated within the root and to a lesser degree in its epidermis, which would suggest that the metals are absorbed by the root tissues and, to a lesser extent, adsorbed on theepidermis.