Stefania Bilardi

Simultaneous removal of CUII, NIII and ZNII by a granular mixture of zero-valent iron and pumice in column systems

AbstractThe granular mixtures between zero-valent iron (ZVI) and other materials (e.g. sand, pumice) have been recently proposed to overcome the problems (e.g. clogging) related to the use of ZVI alone in treatment systems such as permeable reactive barriers or individual potabilisation systems. This paper presents the results of the research activity, carried out by column tests, aimed at comparing the performance of a granular mixture between ZVI and pumice (weight ratio 30:70) and of pure ZVI for the individual and combined removal of CuII, NiII and ZnII. The specific objective was to verify the occurrence of phenomena of mutual interaction and/or competition among contaminants. In fact, although metal removal by ZVI has been extensively documented in the past, the great majority of studies examined either very simple systems (i.e. single metal solutions) or very complicated ones (e.g. real acid mine drainage). In both cases, and for different reasons, the occurrence of mutual interactions (positive or...

Selective removal of heavy metals from landfill leachate by reactive granular filters

The pre-treatment of landfill leachate prior to its co-treatment in the municipal plants of waste water processing could represent an appropriate and cost-effective solution for its management. Pre-treatment is necessary especially to remove heavy metals, which may be transferred to the excess sludge preventing its valorisation. In the present paper, we propose a chemical-physical pre-treatment of leachate using four different granular reactive media able to selectively remove the contaminants present in the leachate. The efficiency of these materials was investigated using synthetic leachate through batch tests and a column test. In the latter case the four materials were placed in two columns connected in series and fed an under constant upward flow (0.5 mL/min). The first column was filled half (50 cm) with a granular mixture of zero valent iron (ZVI) and pumice and half (50 cm) with a granular mixture of ZVI and granular activated carbon (GAC). The second column, which was fed with the effluent of the first column, was filled half with zeolite (chabazite) and half with GAC. Heavy metals were mainly removed by the ZVI/pumice and ZVI/GAC steps with a removal efficiency that was higher than 98, 94 and 90% for copper, nickel and zinc, respectively, after 70 days of operation. Ammonium was removed by zeolite with a removal efficiency of 99% up to 23 days. The average reduction of the chemical oxygen demand (COD) was of 40% for 85 days, whereas chloride and sulphate removal was negligible.

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

ABSTRACT 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). GRAPHICAL ABSTRACT