Improved removal of arsenic from groundwater using pre-corroded steel and iron tailored granular activated carbon

Abstract

The authors have combined corrosion of steel fittings or perforated sheets with granular activated carbon (GAC) that had been pre-treated with Fe(III)-citrate, to produce an innovative and low-maintenance technique for removing arsenic from groundwater. Removal of arsenic was measured using two GAC column configurations: rapid small scale column tests (RSSCT's) and mini-column tests. Independent variables included pH, pre-corrosion procedure, and idling of the column (i.e. intentionally stopping flow for defined times in order to create reducing conditions). Use of corroded steel plus pre-treated GAC removed arsenic to below 10 microg/L for up to 248,000 bed volumes (BV) at pH 6, compared to 7,000 BVs for pre-treated GAC without pre-corroded steel. Performance was not as good at pH 6.5 or 7.5. Idling the system recovered the iron corrosion ability by reducing the passive Fe(III) layer on pre-corroded steel surface, as a result the BVs to arsenic breakthrough was doubled. But idling also caused brief periods of arsenic and iron release after restart, due to reductive dissolution of arsenic-containing ferric oxides. GAC was also effective as filtration media for removal of iron (hydr)oxide particles (and associated arsenic) that was released from the pre-corroded iron.

Metallic iron for water treatment: leaving the valley of confusion

“…Fe 0 materials are of various types (e.g., cast iron, direct reduced iron), alloyed to a large number of elements (e.g., C, Cr, Mn, Ni, S, Si or Ti) and are sometimes embedded in complex composites (e.g., with activated carbon, bentonite, clay, membrane and MnO 2 ) (Ghauch et al 2010;Zou, et al 2010;Ghauch et al 2011). These Fe 0 materials necessarily depict disparities in their intrinsic reactivity but correlating the reactivity to any material characteristic properties, including the nature of alloyed elements, was proven an impossible task (Richardson and Nicklow 2002;Miehr et al 2004;Noubactep et al 2009a;Btatkeu-K et al 2013;Birke et al 2015;Li et al 2016).…”

Predicting the Hydraulic Conductivity of Metallic Iron Filters: Modeling Gone Astray

“…It has been unambiguously demonstrated that all tools used to accelerate lab-scale experiments collectively impair the reliability of the obtained test results [35,[65][66][67]. Relevant tools include adding oxidizing agents to accelerate corrosion [58], increasing flow velocity [34] and using Fe 0 of smaller particle sizes and/or rapid small-scale column tests [65].…”

“…Relevant tools include adding oxidizing agents to accelerate corrosion [58], increasing flow velocity [34] and using Fe 0 of smaller particle sizes and/or rapid small-scale column tests [65]. For the early phase of column operation, methylene blue (MB) discoloration has been proven a powerful indicator of reactivity [68][69][70][71][72][73][74].…”