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 30min, and further enhanced to 97±0.61% after 4h. 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 30min and 76±1.7% at 4h. Higher than 90% bacterial deactivation efficiency was achieved when the ratio between wastewater bacteria population and weight of Fe³⁺-saturated montmorillonite was at <2×10³CFU/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 1h. 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.