Environmental Assessment of In situ Groundwater Remediation with Reduced Iron Reactive Media.

Advancements in groundwater remediation technologies increasingly rely on in situ treatment approaches and reactive nanoparticle materials. Environmental assessments of both trends were conducted for applications where reduced iron media, zero valent iron (ZVI) and iron monosulfide (FeS), are employed. In situ technologies, such as permeable reactive barriers (PRBs), eliminate the need for energy-intensive plume extraction but require greater material resources. The environmental impacts of a PRB and an ex situ pump-and-treat system were compared using life cycle assessment. While the ZVI PRB has better environmental performance in some categories, an alternative reactive media may give significant improvements in global warming potential. The environmental benefits of PRBs are sensitive to the longevity of the reactive medium. The PRB was preferable in all categories when design-life exceeded ten years. Injection of nanosized reactive media can allow installation of PRBs at greater depths than direct emplacement of granular media, but release of engineered nanoparticles may affect soil microbial communities. The effect of nano ZVI (nZVI) on Escherichia coli was investigated under anaerobic conditions in a chemically-defined growth medium buffered at pH 7. E. coli growth was reduced in the presence of 2.9 E-05 M to 5.7 E-03 M nZVI relative to a negative control, and relative growth was a bimodal function of nZVI concentration. Equilibrium speciation modeling of the growth medium in the presence of nZVI predicts low electron activity and high ferrous iron concentrations, which may be related the reduction in growth. FeS nanoparticles are an alternative to nZVI for in situ remediation, and may have similar effects on microorganisms. The effect of FeS on E. coli under anaerobic growth conditions was investigated. E. coli growth was reduced in the presence of 2.6 E-05 M to 5.3 E-3 M FeS. Below the solubility limit, 6.0 E-04 M FeS, relative growth in the presence of FeS was similar to growth in the presence of dissolved sulfide. Relative growth did not decrease with FeS concentration above the solubility. Speciation modeling predicts the formation metal sulfide precipitates as FeS or dissolved sulfide is added, which may be related to the reduction in growth.