Characterizing the impact of MnO2 on the [47], [48] and [49]efficiency of Fe0-based filtration systems

• Fe0/additive mixtures are currently tested for environmental remediation.
• Tools for reliable design of Fe0 walls are urgently needed.
• A volumetric Fe0/sand ratio of 25% has been proven to be the most sustainable.
• Improving Fe0/sand systems by admixing granular MnO2 minerals is tested herein.
• Results clearly demonstrated the suitability of MnO2 addition for better Fe0 filters.

Significant research has been conducted on the design of filtration systems containing metallic iron for environmental remediation (Fe0 walls) over the past 20 years. However, limited information exists on the rationale for sustainable Fe0 walls. Additionally, very limited research has been conducted on the modification of the efficiency of the system by the addition of solid phases. This research aimed at characterizing the impact of reactive natural manganese oxides (MnO2) in influencing the extent of methylene blue (MB) discoloration by a Fe0/sand system in 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 different Fe0/MnO2/sand mixtures. 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 impact of MnO2 on system’s permeability could not be accessed because of the poor mechanic properties of tested minerals. However, the feasibility of sustaining the efficiency of Fe0 walls by admixing granular MnO2 is demonstrated. This tool will help in the development of more sustainable Fe0 walls. Such systems could also lead to substantial improvement of drinking water supply and wastewater treatment in the developing world.