Abstract
Metallic iron (Fe0) has shown outstanding performances for water decontamination and its efficiency has been improved by the presence of sand (Fe0/sand) and manganese oxide (Fe0/MnOx). In this study, a ternary Fe0/MnOx/sand system is characterized for its discoloration efficiency of methylene blue (MB) in quiescent batch studies for 7, 18, 25 and 47 days. The objective was to understand the fundamental mechanisms of water treatment in Fe0/H2O systems using MB as an operational tracer of reactivity. The premise was that, in the short term, both MnO2 and sand delay MB discoloration by avoiding the availability of free iron corrosion products (FeCPs). Results clearly demonstrate no monotonous increase in MB discoloration with increasing contact time. As a rule, the extent of MB discoloration is influenced by the diffusive transport of MB from the solution to the aggregates at the bottom of the vessels (test-tubes). The presence of MnOx and sand enabled the long-term generation of iron hydroxides for MB discoloration by adsorption and co-precipitation. Results clearly reveal the complexity of the Fe0/MnOx/sand system, while establishing that both MnOx and sand improve the efficiency of Fe0/H2O systems in the long-term. This study establishes the mechanisms of the promotion of water decontamination by amending Fe0-based systems with reactive MnOx.
Highlights
Metallic iron (Fe0) has shown outstanding performances for water decontamination and its efficiency has been improved by the presence of sand (Fe0/sand) and manganese oxide (Fe0/MnOx)
Since the 1950s the world is conventionally divided into two groups with regards to the access to safe drinking water: (i) developed countries striving for selecting the best available technology for water treatment, and (ii) developing countries striving for making some appropriate technologies available for their mostly low-income and rural populations[1,2,3]
Research during the past two decades has rediscovered filtration systems based on metallic iron (Fe0) as an affordable, applicable, and efficient water treatment technology for decentralized water supply[3,7,9,10,11,12,13]
Summary
Metallic iron (Fe0) has shown outstanding performances for water decontamination and its efficiency has been improved by the presence of sand (Fe0/sand) and manganese oxide (Fe0/MnOx). Research during the past two decades has rediscovered filtration systems based on metallic iron (Fe0) as an affordable, applicable, and efficient water treatment technology for decentralized water supply (e.g. households and small communities)[3,7,9,10,11,12,13]. Such Fe0 filters are only sustainable upon admixing Fe0 with other aggregates like granular activated carbon, biochar, gravel, magnetite (Fe3O4), manganese oxides ( MnOx), pyrite (FeS2), and s and[10,14,15]. Assigned function Generates contaminant scavengers (FeCPs) Donates electrons to contaminants Sustains iron corrosion (Fe0/GAC cells) Accumulates contaminants for reduction by Fe0 Sustains long-term iron corrosion Scavengers of FeCPs (in-situ coating) Impairs the efficiency of the Fe0 system Sustains long-term iron corrosion Corrodes Fe0 (as cathodic reaction) Scavengers of Fe2+ Sustains long-term iron corrosion
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