Fe3 +-saturated montmorillonite effectively deactivates bacteria in wastewater
Existing water disinfection practices often produce harmful disinfection byproducts. The antibacterial activity of Fe3 +-saturated montmorillonite was investigated mechanistically using municipal wastewater effluents. Bacterial deactivation efficiency (bacteria viability loss) was 92 ± 0.64% when a secondary wastewater effluent was mixed with Fe3 +-saturated montmorillonite for 30 min, and further enhanced to 97 ± 0.61% after 4 h. This deactivation efficiency was similar to that when the same effluent was UV-disinfected before it exited a wastewater treatment plant. Comparing to the secondary wastewater effluent, the bacteria deactivation efficiency was lower when the primary wastewater effluent was exposed to the same dose of Fe3 +-saturated montmorillonite, reaching 29 ± 18% at 30 min and 76 ± 1.7% at 4 h. Higher than 90% bacterial deactivation efficiency was achieved when the ratio between wastewater bacteria population and weight of Fe3 +-saturated montmorillonite was at < 2 × 103 CFU/mg. Furthermore, 99.6–99.9% of total coliforms, E. coli, and enterococci in a secondary wastewater effluent was deactivated when the water was exposed to Fe3 +-saturated montmorillonite for 1 h. Bacterial colony count results coupled with the live/dead fluorescent staining assay observation suggested that Fe3 +-saturated montmorillonite deactivated bacteria in wastewater through two possible stages: electrostatic sorption of bacterial cells to the surfaces of Fe3 +-saturated montmorillonite, followed by bacterial deactivation due to mineral surface-catalyzed bacterial cell membrane disruption by the surface sorbed Fe3 +. Freeze-drying the recycled Fe3 +-saturated montmorillonite after each usage resulted in 82 ± 0.51% bacterial deactivation efficiency even after its fourth consecutive use. This study demonstrated the promising potential of Fe3 +-saturated montmorillonite to be used in applications from small scale point-of-use drinking water treatment devices to large scale drinking and wastewater treatment facilities.