Modeling the Permeability Loss of Metallic Iron Water Filtration Systems

Abstract

Over the past 30 years the literature has burgeoned with in situ approaches for groundwater remediation. Of the methods currently available, the use of metallic iron (Fe0) in permeable reactive barrier (PRB) systems is one of the most commonly applied. Despite such interest, an increasing amount of experimental and field observations have reported inconsistent Fe0 barrier operation compared to contemporary theory. In the current work, a critical review of the physical chemistry of aqueous Fe0 corrosion in porous media is presented. Subsequent implications for the design of Fe0 filtration systems are modeled. The results suggest that: (i) for the pH range of natural waters (>4.5), the high volumetric expansion of Fe0 during oxidation and precipitation dictates that Fe0 should be mixed with a non‐expansive material; (ii) naturally occurring solute precipitates have a negligible impact on permeability loss compared to Fe0 expansive corrosion; and (iii) the proliferation of H2 metabolizing bacteria may contribute to alleviate permeability loss. As a consequence, it is suggested that more emphasis must be placed on future work with regard to considering the Fe0 PRB system as a physical (size‐exclusion) water filter device.

Testing the suitability of metallic iron for environmental remediation: Discoloration of methylene blue in column studies

“…filters is still poorly understood [16]. The present work and related studies [59][60][61] suggest that this issue was even not properly addressed.…”

Appropriate technology for domestic wastewater management in under-resourced regions of the world

“…biphenyls, detergents, dyes, fertilizers, greases, hydrocarbons, oils, pharmaceuticals, personal care products, pesticides, plasticizers, phenols, and surfactants) in aqua system has prompted the development of efficient, applicable, and affordable technologies, in particular, in remote, low-income communities. The use of metallic iron (Fe 0 ) beds has been demonstrated as such an appropriate technology (Ghauch 2015;Noubactep et al 2009;Litter et al 2010;Noubactep 2010a;Noubactep and Schöner 2010;Giles et al 2011;Noubactep 2013a) and design criteria presented (Noubactep and Caré 2010;Noubactep et al 2012a, b;Bilardi et al 2013a, b;Caré et al 2013;Btatkeu-K et al 2014). The suitability of Fe 0 to treat a complex mixture of micro-pollutants arises from the fact that the primary removal mechanism is not a specific one.…”

Testing Metallic Iron Filtration Systems for Decentralized Water Treatment at Pilot Scale

“…The presentation herein is limited to granular mm-and μm-scale particles (d > 215 μm) [25,98]. Furthermore, the suitability of micron scale Fe 0 particles arises from the evidence that resulting system (Fe 0 filters) must be efficient in the long term, with sub-micron scale particles becoming exhausted over relatively short timescales [25,71,72,99,100].…”

“…This clarification coupled to the consideration of the formation of voluminous Fe 0 corrosion products is the theoretical starting point for the design of next generation Fe 0 filters [16,17,25,98,100,[120][121][122][123]. No consideration of these key issues has led to controversial reports which render the assessment of progress in designing Fe [8,9,54,58,[88][89][90][124][125][126].…”

“…These authors used a 1:1 Fe 0 :sand (vol/vol) for methylene blue discoloration in column studies for four and three months respectively and observed that at the influent of the column, about 3 cm was brown colored (Figure 3) and hardly compacted, while the remaining Fe 0 /sand layer was less or not compacted and black colored. Recent works have recalled that the availability of dissolved O2 is the major factor causing particle cementation and permeability loss [25,100,122,123]. However, even without this "recent" knowledge, a pragmatic approach would have consisted of comparing the density of Fe 0 (7.8 g/cm 3 ) and Fe oxides (e.g., β-FeOOH; 3.6 g/cm 3 ) [137].…”