Enhancing the Sustainability of Household Fe⁰/Sand Filters by Using Bimetallics and MnO₂

Abstract

Filtration systems containing metallic iron as reactive medium (Fe0 beds) have been intensively used for water treatment during the last two decades. The sustainability of Fe0 beds is severely confined by two major factors: (i) reactivity loss as result of the formation of an oxide scale on Fe0 and (ii) permeability loss due to pore filling by generated iron corrosion products. Both factors are inherent to iron corrosion at pH > 4.5 and are common during the lifespan of a Fe0 bed. It is of great practical significance to improve the performance of Fe0 beds by properly addressing these key factors. Recent studies have shown that both reactivity loss and permeability loss could be addressed by mixing Fe0 and inert materials. For a non‐porous additive like quartz, the threshold value for the Fe0 volumetric proportion is 51%. Using the Fe0/quartz system as reference, this study theoretically discusses the possibility of (i) replacing Fe0 by bimetallic systems (e.g., Fe0/Cu0), or (ii) partially replacing quartz by a reactive metal oxide (MnO2 or TiO2) to improve the efficiency of Fe0 beds. Results confirmed the suitability of both tools for sustaining Fe0 bed performance. It is shown that using a Fe0:MnO2 system with the volumetric proportion 51:49 will yield a filter with 40% residual porosity at Fe0 depletion (MnO2 porosity 62%). This study improves Fe0 bed design and can be considered as a basis for further refinement and detailed research for efficient Fe0 filters.

Making Fe0-Based Filters a Universal Solution for Safe Drinking Water Provision

“…This is the fundamental mechanism of contaminant removal in Fe 0 /H 2 O systems [33]. The role of MnO 2 in sustaining the efficiency of Fe 0 filters was explained as follows [105][106][107][108][109][110]: MnO 2 uses Fe 2+ from Fe 0 oxidative dissolution by water (Equation (1)) for its reductive dissolution (Equation (2)):…”

“…Despite stoichiometric disadvantage, small amounts of MnO 2 will act as a catalyst because MnOOH is permanently recycled into MnO 2 [110]. This catalytic aspect has been put forward to rationalize the sustainability of SONO arsenic filters [17,25,53].…”

Impact of MnO2 on the efficiency of metallic iron for the removal of dissolved CrVI, CuII, MoVI, SbV, UVI and ZnII

“…The greater pH increase in the presence of MnO 2 is a strong experimental evidence for the suitability of MnO 2 to sustain the reactivity of Fe 0 at the long-term ( [19] and ref. cited therein).…”

“…The suitability of MnO 2 to sustain Fe 0 reactivity for the contaminant removal is also confirmed. The importance of this latter aspect has been recently presented in theoretical works on the suitability of MnO 2 to sustain the efficiency of household water filters [19].…”

The Suitability of Pozzolan as Admixing Aggregate for Fe0-Based Filters

“…This observation was the starting point for the manufacture of a proprietary porous iron composite in which the initial porosity leaves room for expansive iron corrosion products [52]. The replacement of a fraction of Fe 0 by a nonexpansive material (e.g., gravel, sand, pumice) [14,55,56] was therefore found as an alternative approach.…”