Nanosilver-impregnated and acid-treated vermiculite within water filtration system and its dual function in bacterial disinfection and silver reabsorption

Antibacterial activity of silver-impregnated vermiculite and silver removal capability of acid-treated vermiculite (Verm-A) were assessed through 4-stage water filtration systems. The antibacterial vermiculite was prepared through cation exchange process in silver nitrate solutions of 0, 500, 1000, and 2000 mgl-1, named Verm-B0, Verm-B500, Verm-B1000, and Verm-B2000, respectively. The Verm-A was only treated with 1 M HCl to increase its negative zeta potential. Bacterium Aeromonas hydrophila was inoculated into the filtration systems and then total colony forming units in water samples was enumerated for 96 h. Flame atomic absorption spectrometer showed the maximum silver adsorption (49.17 mg/g) by Verm-B2000. Scanning electron microscopy micrographs illustrated silver with nano dimension crystallites with the average sizes of 274.808, 194, 162.258 nm on the surface of Verm-B2000, Verm-B500, and Verm-B1000, respectively. All the Verm-B products were approved to possess a strong antibacterial activity, with reducing the bacterial growth over 95% in all of the filtration systems containing Verm-B500-2000. The highest log reduction value of 3.47 CFU mL-1 at 96 h was observed for the filtration system containing Verm-B1000. The percentage of silver released from the total Ag in Verm-B500 was 32.36%, Verm-B1000 27.87%, and Verm- B2000 17.24%; of these amounts, 90.9%, 81.8%, and 75.7% were reabsorbed respectively, by Verm-A. The observed bactericidal efficiency could open an avenue to use silver-impregnated vermiculite in water treatment. Moreover, acid treated vermiculite could be introduced as an affordable absorbent for removal of silver from water filtration system, industrial wastewater and reduce metallic environmental contaminants.