Behavior of multi-layer permeable reactive barriers for groundwater remediation

This paper aims to evaluate the efficiency of a multilayer configuration of a permeable reactive barrier (PRB) made up of granular mixtures of zero valent iron (ZVI) and lapillus. The latter is a volcanic material used to disperse ZVI particles. A high dispersion of ZVI improves the long-term hydraulic conductivity but can significantly reduce reactivity due to the lower amount of ZVI. In this research, the performance of two different combinations of a two-layer configuration was studied by means of long-term column tests. The first layer, named "pre-treatment layer", had a thickness of 4 cm and a volumetric ratio (ZVI/lapillus) of 10:90 or 05:95, while the second layer had a volumetric ratio (ZVI/lapillus) of 20:80. A single layer configuration made only of the 20:80 ZVI/lapillus was used as a bench-mark. The three tests were performed using a multi-contaminated solution of copper, nickel and zinc. Test results showed an early loss of the hydraulic conductivity in the single layer configuration and an increase of PRB longevity by 68 % in the presence of the pre-treatment layer. The pre-treatment zone containing 10 % ZVI delayed the clogging phenomenon, while the zone with 5 % ZVI ensured both the correct long-term hydraulic behavior and a removal efficiency higher than 77.6 % for Nickel and 99 % for copper and zinc at 23 cm of thickness for at least two months.(c) 2023 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).