Enhancement of plasma bacterial inactivation by ferric iron supplementation

In the present paper, we report results on the plasma bacterial inactivation in the presence of ferric ions, added to the Fenton reaction medium. Fenton reaction is a catalytic reaction of hydrogen peroxide conversion into a highly reactive hydroxyl radical in the presence of ferric ions. Non-thermal plasma jet was used as plasma source, and Escherichia coli (E. coli) was used as bacterial sample. Ferric sulfate was used as source of ferric ions. Inactivation experiments to E. coli suspension added ferric sulfate were carried out. First, effect to survival rate caused by ferric sulfate and magnesium sulfate were compared. Magnesium sulfate contains divalent metal ion without Fenton catalytic activity. Only ferric sulfate enhanced inactivation effect. Then, experiment with ferric sulfate at various concentrations was carried out. In result, the enhancement of inactivation was confirmed at the optimum concentration. Though, ferric sulfate in concentration higher than optimum level rather suppressed inactivation effect. The enhancement was not reproduced by addition of hydrogen peroxide in concentration similar to sample after plasma treatment. In conclusion, addition of ferric sulfate in optimum concentration can enhance inactivation effect. It can be expected as new control technique for non-thermal plasma bacterial inactivation.