Mathematical models of cobalt and iron ions catalyzed microwave bacterial deactivation

Abstract

Time differences for Enterococcus faecalis, Staphylococcus aureus, and Escherichia coli survival during microwave irradiation (power 130 W) in the presence of aqueous cobalt and iron ions were investigated. Measured dependencies had "bell" shape forms with maximum bacterial viability between 1 - 2 min becoming insignificant at 3 minutes. The deactivation time for E. faecalis, S. aureus and E.coli in the presence of metal ions were smaller compared to a water control (4 -5 min). Although various sensitivities to the metal ions were observed, S. aureus and E. coli and were the most sensitive for cobalt and iron, respectively. The rapid reduction of viable bacteria during microwave treatment in the presence of metal ions could be explained by increased metal ion penetration into bacteria. Additionally, microwave irradiation may have increased the kinetic energy of the metal ions resulting in lower survival rates. The proposed mathematical model for microwave heating took into account the "growth" and "death" factors of the bacteria, forming second degree polynomial functions. Good relationships were found between the proposed mathematical models and the experimental data for bacterial deactivation (coefficient of correlation 0.91 - 0.99).

Figure 1:

Effect of cobalt ions on microwave disinfection of E. faecalis. Shows the effect that cobalt ions (solid line) have on the deactivation of E. faecalis (n = 10) during microwave heating compared to a distilled water control (dotted line). Cobalt ions reduced the time necessary for microwave disinfection of E. faecalis.

Figure 2:

Effect of cobalt ions on microwave disinfection of E. coli. Illustrates the effect that cobalt ions (solid line) have on the deactivation of E. coli (n = 10) during microwave heating compared to a distilled water control (dotted line). Cobalt ions had negligible effects on the microwave disinfection of E. coli.

Figure 3:

Effect of cobalt ions on microwave disinfection of S. aureus. Demonstrates the effect that cobalt ions (solid line) have on the deactivation of S. aureus (n=10) during microwave heating compared to a distilled water control (dotted line). Cobalt ions appeared to enhance microwave radiation’s disinfection ability for S. aureus.

Figure 4:

Effect of iron ions on microwave disinfection of E. faecalis. Illustrates the effect that iron ions (solid line) have on the deactivation of E. faecalis (n = 10) during microwave heating compared to a distilled water control (dotted line). Iron ions had a trivial effect on microwave disinfection of E. faecalis.

Figure 5:

Effect of iron ions on microwave disinfection of S. aureus. Illustrates the effect that iron ions (solid line) have on the deactivation of S. aureus (n=10) during microwave heating compared to a distilled water control (dotted line). Similar to E. faecalis, iron ions had a negligible effect on microwave disinfection of S. aureus.

Figure 6:

Effect of iron ions on microwave disinfection of E. coli. Illustrates the effect that iron ions (solid line) have on the deactivation of E. coli (n = 10) during microwave heating compared to a distilled water control (dotted line). Unlike results from E. faecalis and S. aureus, iron ions reduced the disinfection time from four minutes for the distilled water control (dotted line) to under one minute for the iron enhanced group (solid line).