Metal removal by pine bark compost using a permeable reactive barrier device at laboratory scale

Abstract

Environmental contextPermeable reactive barriers are a developing technology to clean up contaminated groundwater. The contaminant plume moves through a reactive material placed below ground that retains or degrades the pollutants. This study shows that pine bark compost strongly adsorbs and retains metals, mostly by interaction with the organic matter of the compost, and thereby serves as a suitable reactive filler material to clean up contaminated groundwater. AbstractPermeable reactive barriers (PRBs) are in situ systems for groundwater remediation, consisting of a screen perpendicular to the flow of contaminated groundwater filled with a material capable of retaining or degrading pollutants. The use of waste materials as reactive substrates in PRBs is of particular interest owing to the possibility of their reutilisation and their generally lower cost. With this aim, the sorption capacity for copper, nickel and zinc of pine bark compost (PBC) was evaluated in competitive batch experiments that showed that metal adsorption is a rapid process and that adsorption capacities followed the sequence Cu>Ni>Zn, with maximum adsorption capacities of 0.157mmolg–1 for Cu2+, 0.052mmolg–1 for Ni2+, 0.046mmolg–1 for Zn2+ and 0.259mmolg–1 for the sum of the three metals. Subsequently, a dynamic percolation experiment was carried out with a multi-metal solution prepared with 50mgL–1 of Cu, Ni and Zn in 0.01M KNO3 as saline background, using an experimental device that reproduced a PRB at laboratory scale. Metal retention ranged from 92 to 99% (Cu>Ni>Zn). The metals were strongly retained by the filling material because low desorption was detected by subsequent leaching with 0.01M KNO3 (0.3, 1.8 and 4.1% of the previously adsorbed metal for Cu, Ni and Zn respectively). The results show that PBC is a potential candidate as a filler material for the retention of cationic metals in permeable reactive barriers.