Sulfonated Poly(Styrene-Isobutylene-Styrene) Membranes with Counter-Ion Substitution for the Inactivation of Pathogens in Water

In this study, we explore the use of sulfonated poly(styrene-isobutylene-styrene) (SIBS) polymer membranes for the inactivation of Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) in surface waters, particularly when cupric (${\mathrm{Cu}}^{2+}$) and ferric (${\mathrm{Fe}}^{3+}$) counter-ions were cross-linked to the sulfonic domains of the membrane. The antibacterial evaluation of copper-exchanged and iron-exchanged sulfonated SIBS was carried out by assaying the presence of E. coli and E. faecalis after the membranes were brought into contact with bacterial suspensions from certified bacterial strains and water samples from a natural surface water source. Overall, the cell viability results obtained suggest that copper-exchanged sulfonated SIBS successfully inactivated both pathogenic bacteria. Although the extent of inactivation varied depending on the water source, treatment time, and initial population of bacterial suspension, copper-exchanged sulfonated SIBS was more selective to E. coli and iron-exchanged sulfonated SIBS was more selective to Enterococci bacteria. It was also observed that the inactivation of E. coli was strongly influenced by the degree of sulfonation (DS) since it was found to be dependent on the quantity of the ${\mathrm{Cu}}^{2+}$ exchanged. Finally, the membranes showed roughness changes upon exposure to the bacterial suspensions; however, they continued to be effective upon reuse.