Alternative materials for permeable reactive barriers

There is an increasing interest in the development of in situ methods of contaminated soil and groundwater treatment, such as soil stabilization, permeable reactive barriers and soil bed filters. Because these techniques are passive, their operation and maintenance costs are low. In this study, peat moss has been investigated as a low-cost alternative sorption material for permeable reactive barriers and soil bed filters. Peat moss showed the highest sorption capacity for metals among the alternative products studied in a comparative batch test with bark, sawdust, fiber ashes, shrimp shell and seaweed. Batch tests and column experiments were carried out with both artificial solutions and highly contaminated landfill leachate. All the metals studied (Cd, Pb, Ni, Cu, Zn and Cr) were removed by peat by more then 70% from single metal artificial solutions in a concentration range of 0,1-10 mgl-1. The lower performance (33-40% for Zn and Cd) of the sorbent for complex solutions, i.e. real leachates, suggests competitive sorption. Freundlich adsorption isotherms were plotted and adsorption evaluated from the Freundlich constants Kf and n. The influence of different factors on sorption onto peat i.e. variation in metal concentrations, pH and competition between metals were investigated. The material used was characterized by measuring dry weight, lost of ignition, grain size distribution, metal and organic content, pH, buffer capacity, conductivity, redox potential, ion exchange capacity, pore size volume, density, hydraulic conductivity among other parameters. The results obtained provide important information on peat moss adsorption capacity under different environmental conditions, which can be used in the design and construction of permeable reactive barriers or soil bed filters