Arsenic Remediation Field Study Using a Sulfate Reduction and Zero‐Valent Iron PRB

Abstract

Toxic and carcinogenic effects of arsenic in drinking water continue to impact people throughout the world and arsenic remains common in groundwater at cleanup sites and in areas with natural sources. Advances in groundwater remediation are needed to attain the low concentrations that are protective of human health and the environment. In this article, we present the successful use of a permeable reactive barrier (PRB) utilizing sulfate reduction coupled with zero‐valent iron (ZVI) to remediate the leading edge of a dissolved arsenic plume in a wetland area near Tacoma, Washington. A commercially available product (EHC‐M®, Adventus Americas Inc., Freeport, Illinois) that contains ZVI, organic carbon substrate, and sulfate was injected into a reducing, low‐seepage‐velocity aquifer elevated in dissolved arsenic and iron from a nearby, slag‐containing landfill. Removal effectiveness was strongly correlated with sulfate concentration, and was coincident with temporary redox potential (Eh) reductions, consistent with arsenic removal by iron sulfide precipitation. The PRB demonstrates that induced sulfate reduction and ZVI are capable of attaining a regulatory limit of 5 µg/L total arsenic, capturing of 97% of the arsenic entering the PRB, and sustaining decreased arsenic concentrations for approximately 2 years, suggesting that the technology is appropriate for consideration at other sites with similar hydrogeochemical conditions. The results indicate the importance of delivery and longevity of minimum sulfate concentrations and of maintaining sufficient dissolved organic carbon and/or microscale ZVI to precipitate FeS, a precursor phase to arsenic‐bearing pyrite that may provide a stable, long‐term sink for arsenic.

Uptake of nickel by synthetic mackinawite

“…The formation of mackinawite as an authigenic precipitate in subsurface installations of granular iron and/or organic carbon(permeable reactive barriers) for treating contaminated groundwater is well documented (e.g., Phillips et al, 2000, Furukawa et al, 2002, Beaulieu and Ramirez, 2013. Long-term studies have shown that sulfate reducing processes are sustainable in these remediation systems for decadal time scales (Wilkin et al, 2014) and accumulation of mackinawite within the reactive medium provides additional pathways for treatment of inorganic and organic contaminants via sorption, reduction, and/or degradation processes.…”

Arsenic Adsorption onto Minerals: Connecting Experimental Observations with Density Functional Theory Calculations

“…For example, an in situ study of an alkaline aquifer showed relatively low adsorption of iAs [37]. Conversely, a permeable reactive barrier study showed As removal to <5 μg/L due to induced sulfate reduction and the presence of zero-valent Fe [38], and experiments with household sand filters in Vietnam were able to reduce As concentrations in drinking water to <10 μg/L with a 40% success rate [39]. Laboratory and field experiments with household zero-valent Fe filters showed similarly effective results in Bangladesh [40].…”

An Injectable Apatite Permeable Reactive Barrier for In Situ 90Sr Immobilization

“…Researchers have studied various reactive materials, including zero-valent iron (Blowes and Ptacek 1992;Matheson and Tratnyek 1993;Borden et al 1997;Wilkin et al 2003), clinoptilolite (Park et al 2002;Seneca and Rabideau 2013), and various organic materials (Ahmad et al 2007;Robertson et al 2007). To eliminate limitations associated with excavation depth, researchers have also studied various injectable PRB technologies, including in situ reduction of iron present in the sediments (Istok et al 1999;Fruchter et al 2000) and injection of micron-and nano-scale zero-valent iron (Oostrom et al 2007;Chen et al 2010;Truex et al 2010;Beaulien and Ramirez 2013).…”