Optimal design of ZVI/lapillus mixtures for nickel removal in permeable reactive barriers

The remediation of contaminated groundwater, through the technology of permeable reactive barriers (PRB), involves the use of a reactive medium able to reduce the concentration of contaminants as long as remediation targets are achieved. In the present study, the use of granular mixtures composed of zero valent iron (ZVI) and lapillus for the treatment of nickel contaminated groundwater is proposed. Through short and long term column experiments, the effects of the following were analysed: i) ZVI percentage per unit volume, ii) reactive medium thickness, iii) flow velocity and iv) initial nickel concentration, on the breakthrough point occurrence (point where a rapid increase in nickel concentration in the effluent is observed). The optimal mixture composition (i.e. the optimal ZVI content per unit volume) was defined when the reactive medium was able to keep its reactivity and hydraulic conductivity for the time necessary for remediation. This capacity, as shown in this study, depends on the propagation velocity of the contamination front through the reactive medium.