Microbial mortality behavior promoted by silver (Ag + /Ag o )-modified zeolite-rich tuffs for water disinfection.

Background: In developing countries, death due to diseases caused by fecal-oral ingestion can be avoided by taking action on drinking water issues. Adequate access to water treatment systems to reduce infections is a critical cause. Silver has been used as an antibacterial product, including biomedical applications. Therefore, in this paper, the effect of the chemical speciation of silver from silver-modified zeolite-rich tuffs on the mortality of Escherichia coli ( E. coli ), Streptococcus faecalis ( S. faecalis ) and Candida albicans ( C. albicans ) suspended in aqueous solution was investigated for disinfection purposes.
Methods: The following aspects were considered to develop the investigation: a) the technique to prepare the modified zeolitic materials, either with ionic silver or silver nanoparticles, which were obtained in two ways: one, with grapefruit extract and the second, by using non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates; b) the response of the prokaryotes (bacteria) and eukaryote (yeast) microorganisms to disinfectant agents in batch systems; c) the disinfection processes as a function of time to obtain kinetics parameters; and d) the kinetics of the silver release from the silver-modified zeolite-rich tuffs, considering the models of Higuchi and Korsmeyer. The zeolitic materials were characterized by low-vacuum scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).
Results: The non-thermal plasma reduced ionic silver is more efficient at generating silver compounds with several oxidation states, which are essential during the microbial inhibition process. For the bacterial ( E. coli and S. faecalis ), the materials with nanoparticles were efficient to inactivate them. However, the yeast ( C. albicans ) reaches the total inactivation when the zeolitic material contains ionic silver in the crystalline network.
Conclusion: The E. coli , S. faecalis and C. albicans survival behavior suspended in aqueous solutions after contact with Ag-modified natural zeolites depends on the chemical speciation of the silver present in these materials, Ag ⁺¹ in the case of OAg _i Z or nanoparticles of Ag ^o promoted by the grapefruit extract (OAg _npT Z), as well as by non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates (OAg _npP Z). In general, the concentration of silver in the aqueous solution after the disinfection process cannot exceed the recommended levels established for international organizations. The OAg _npP Z is a potential microbicide agent against E. coli and C. albicans , and the OAg _{n pT} Z for F. faecalis .Graphical abstract ARTWORK.
Competing Interests: Competing interestsThe authors declare that they have no competing interests.
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