Impact of ZVI and sulfidated ZVI on sulfate-reducing microbial communities and implications for groundwater remediation

Abstract

Sulfur-modified zero valent iron (ZVI) is a common groundwater remediation strategy, and biologically produced sulfur species may enhance ZVI reactivity and specificity at remediation sites. However, the impact of ZVI on the indigenous sulfate-reducing bacteria (SRB) that produce reduced sulfur has not been well explored, and this is important for sustained particle activity. We assessed the influence of original and sulfur-modified (“sulfidated”) ZVI particles on pure culture Desulfovibrio desulfuricans and an SRB aquifer enrichment culture. Particles examined included lab-synthesized nanoscale ZVI (nZVI), Alfa Aesar iron powder (ZVIAA; micron-sized), and commercially available Peerless iron filings (ZVIPLS; micron-sized). Results show that sulfidated ZVI are most compatible with SRB when particles are mesoscale and highly pure; sulfate reduction was most rapid with ZVIAA for both timescales. Sulfidation reduces methanogenic growth in sulfate-reducing mixed communities. Archaeal differences are most pronounced with nZVI (relative abundance of 25.8% [as-synthesized] verses 1.1% [sulfidated]) but sulfidation of ZVIPLS also reduces methanogens (10.1% [as-synthesized] verses 4.6% [sulfidated]). Sulfidation of all particles shifts microbial community composition, and resulting consortia are distinct from particle-free incubations but sustain sulfate-reducing activity. Overall, our data demonstrate that pre-sulfidated particles are less likely to inhibit sulfate-reducing activity, providing the first direct evidence that sulfidated ZVI can be compatible with SRB over different timescales. These findings support the feasibility of integrated ZVI-SRB strategies for in situ remediation under sulfidic subsurface conditions.