Characterizing the impact of MnO2 on the efficiency of Fe0-based filtration systems
Résumé
Significant research has been conducted on the design of filtration systems containing metallic iron (Fe0 filters) over the past 20 years. However, limited information exists on the rationale for sustainable Fe0 filters. Additionally, very limited research has been conducted on the modification of the efficiency of the system by the addition of solid phases. Therefore, efficient tools for sustaining Fe0 reactivity and thus system's efficiency are needed. This research aimed at characterizing the impact of reactive manganese oxides (MnO2) in influencing the extent of methylene blue (MB) discoloration by a Fe0/sand system in a gravity driven column experiments. A total of seven columns were used in parallel experiments. Investigated systems are: pure Fe0, pure sand, Fe0/sand mixture and four Fe0/MnO2/sand mixtures (four different MnO2 minerals). The volumetric ratio of Fe0 in hybrid systems was 30 %. In three-components-systems, the volumetric ratio of each additive was 35%. Each system was characterized by the time-dependent evolution of the pH value, the iron and MB breakthrough, and the evolution of the hydraulic conductivity (permeability). Results showed enhanced MB discoloration in all Fe0/MnO2/sand systems relative to the Fe0/sand system. The presence of MnO2 also enabled better system's permeability. Thus, the feasibility of sustaining the efficiency of Fe0 filters by admixing granular MnO2 is demonstrated. This tool will help in the development of more sustainable Fe0 filters. Such systems could lead to substantial improvement of water supply in the developing world.