Enhanced Biogenic Sulfidation of Zero-Valent Iron in Columns: Implications for Promoting Dechlorination in Permeable Reactive Barriers.

Biogenic sulfidation of zero-valent iron (ZVI) using sulfate reducing bacteria (SRB) has shown enhanced dechlorination rates comparable to those produced by chemical sulfidation. However, controlling and sustaining biogenic sulfidation to enhance in situ dechlorination are poorly understood. Detailed interactions between SRB and ZVI were examined for 4 months in column experiments under enhanced biogenic sulfidation conditions. SRB proliferation and changes in ZVI surface properties were characterized along the flow paths. The results show that ZVI can stimulate SRB activity by removing excessive free sulfide (S2-), in addition to lowering reduction potential. ZVI also hinders downgradient movement of SRB via electrostatic repulsion, restricting SRB presence near the upgradient interface. Dissolved organic carbon (e.g., >2.2 mM) was essential for intense biogenic sulfidation in ZVI columns. The presence of SRB in the upgradient zone appeared to promote the formation of iron polysulfides. Biogenic FeSx deposition increased the S content on ZVI surfaces ∼3-fold, corresponding to 3-fold and 2-fold improvements in the trichloroethylene degradation rate and electron efficiency in batch tests. Elucidation of SRB and ZVI interactions enhances sustained sulfidation in ZVI permeable reactive barrier.

Transport of nanoscale zero-valent iron in saturated porous media: Effects of grain size, surface metal oxides, and sulfidation.

Knowledge of the fate and transport of nanoscale zero-valent iron (nZVI) in saturated porous media is crucial to the development of in situ remediation technologies. This work systematically compared the retention and transport of carboxymethyl cellulose (CMC) modified nZVI (CMC-nZVI) and sulfidated nZVI (CMC-S-nZVI) particles in saturated columns packed with quartz sand of various grain sizes and different surface metal oxide coatings. Grain size reduction had an inhibitory effect on the transport of CMC-S-nZVI and CMC-nZVI due to increasing immobile zone deposition and straining in the columns. Metal oxide coatings had minor effect on the transport of CMC-S-nZVI and CMC-nZVI because the sand surface was coated by the free CMC in the suspensions, reducing the electrostatic attraction between the nZVI and surface metal oxides. CMC-S-nZVI displayed greater breakthrough (C/C0 = 0.82-0.90) and higher mass recovery (84.9%-89.3%) than CMC-nZVI (C/C0 = 0.70-0.80 and mass recovery = 70.9%-79.6%, respectively) under the same experimental conditions. A mathematical model based on the advection-dispersion equation simulated the experimental data of nZVI breakthrough curves very well. Findings of this study suggest sulfidation could enhance the transport of CMC-nZVI in saturated porous media with grain and surface heterogeneities, promoting its application in situ remediation.

Antitumor and immunomodulatory activity of Astragalus membranaceus polysaccharides in H22 tumor-bearing mice.

In the present study, we investigated the antitumor and immunomodulatory activity of Astragalus membranaceus polysaccharide (AMP) on liver cancer using murine H22 hepatocarcinoma model. The results showed that AMP (100 and 400 mg/kg) could effectively inhibit the solid tumor growth of H22 hepatocarcinoma transplanted in BALB/c mice. Besides, the body weight, spleen/thymus indexes and phagocytotic function of macrophage of H22 tumor bearing mice were also improved in two AMP treated groups. Furthermore, AMP treatment could promote the secretion of IL-2, IL-12 and TNF-α and decreased IL-10 level in serum. Taken together, these findings indicate that AMP has antitumor activity in vivo at least partly via improving immune responses of host organism, and seems to be safe and effective for the use of anti-tumor therapy.