Bacterial capture and inactivation in sand filtration systems with addition of zero-valent iron as permeable layer under both slow and fast filtration conditions

Abstract

To improve bacterial capture performance and inactivate bacteria, zero-valent iron (ZVI) were added into sand columns as permeable filtration media. Both Gram-negative Escherichia coli and Gram-positive Bacillus subtilis (1.25 ×107 cells/mL) could be completely retained in 10 wt% ZVI amended sand columns in different ionic strength solutions (1–100 mM NaCl) at both slow (4 m/day) and fast (90 m/day) flow velocities. The strong adsorption property of ZVI contributed to the improved bacterial capture performance of sand columns. Moreover, ZVI could inactivate nearly all captured bacteria. Clearly, ZVI added as permeable layer not only could significantly enhance bacterial capture but also would inactivate the captured bacteria. ZVI could destroy the structure of extracellular polymeric substance and cell membrane. Intracellular oxidative stress was then increased and ATP content was decreased, causing bacterial death. Furthermore, high bacterial capture efficiencies were achieved with the coexisting of humic acid (0.2–5 mg/L), in actual river water samples, and longtime filtration processes. ZVI could be regenerated and reused as permeable layer to efficiently capture bacteria. Furthermore, sand columns with 10 wt% ZVI amendment could completely capture and inactivate 4.0 × 106 cells/mL algae. Clearly, ZVI amended sand filtration systems have potentials to purify water contaminated by pathogenic bacteria and algae.