Removal of heavy metals from landfill leachate using zero valent iron and granular activated carbon

The possibility of a landfill leachate pre-treatment, aiming at heavy metals removal, by means of either zero valent iron (ZVI), or granular activated carbon (GAC) or by a mixture of the two materials, was investigated in this paper through batch and column tests. For this purpose, a synthetic landfill leachate containing heavy metals (i.e. Cu, Ni, Zn), chloride, sulphates, ammonium and organic matter was prepared. Batch tests results demonstrated the efficiency of ZVI, GAC and ZVI/GAC mixture in heavy metals removal (efficiency > 90%) and their negligible effect on the other contaminants. Column tests showed as pure ZVI is by far more efficient than pure GAC in the long term. The influence of humic acids (HA) on the reactive and hydraulic behaviour of ZVI was also studied through column tests. The presence of HA in the leachate caused a reduction of ZVI removal efficiency and a considerable decrease in its hydraulic conductivity. Results of a column test carried out using the ZVI/GAC granular mixture showed as the removal efficiency over time ranges from 100% to 89% for Cu, from 93% to 80% for Ni and from 98% to 95% for Zn. The use of a filter filled with the ZVI/GAC mixture could find application for leachate pre-treatment having the objective of removing heavy metals prior the final co-treatment with municipal wastewater minimizing adverse side effect on the process (e.g. transfer of heavy metals in the excess sludge to be used in agriculture).