Plasma-activated saline chemistry: unveiling bactericidal mechanisms and assessment of nitrogen fixation potential

Abstract

This thesis presents an in-depth analysis of the liquid phase chemistry inherent to plasma-treated saline solutions within a controlled experimental setup having identical operational conditions as employed in biofilm inactivation studies. The work primarily focuses on quantifying and identifying chemistry enabling bacterial inactivation by evaluating the key reactive species, including hydrogen peroxide (H2O2), nitrates (NO3-), nitrites (NO2-) hypochlorous acid (HOCl), Ozone (O3) and peroxynitrous acid (ONOOH). I assessed the production of these species systematically for different plasma treatment times of up to 10 minutes using a combination of absorption spectroscopy, probe molecule, and colorimetric approaches. The results were analyzed using solution phase chemical kinetics adopted from the literature. These calculations were also used to derive the peroxynitrite concentrations from the experimental results obtained for H2O2, NO2- concentrations, and pH data. The analysis of the obtained results shows that long-lived species with exception of ozone are not directly responsible for bacterial inactivation although the model shows that peroxynitrite concentration of 0.48 µM could be produced which is likely a contribution factor to observed biocidal impact. While the plasma source is highly effective in producing reactive nitrogen species with bactericidal action for decontamination purposes, an analysis of the device's potential for sustainable nitrogen fixation shows modest energy efficiencies.