## 3 Results and Discussion
### Microbiological Analysis
The average pH of the tested diatomaceous earth samples ranged from 6.20 to 6.33, i.e., it can be considered close to neutral and thus favorable for both groups of microorganisms [60]. Therefore, it suggests that the pH of diatomaceous earth was not a factor in the decrease in the number of the analyzed microorganisms (Figure 6). Statistical analysis confirmed the results obtained in this study. The differences in microbial abundance between the proposed variants of the plasma treatment process were found to be statistically significant. Additionally, statistical analysis of the dependence of the average microbial abundance in the tested samples on the plasma exposure time confirmed a high negative correlation between these values. The correlation coefficient for bacteria was r = \(-\)0.89 and for yeast it was r = \(-\)0.98 (\(p<0.05\)). Figure 5: Logarithmic CFU reduction of microorganisms colonizing diatomaceous earth for different plasma treatment times. To the best of our knowledge, there are currently no published study results on using non-equilibrium plasma to remove microbial contaminants from the porous surface of diatomaceous earth. Therefore, our analyzes fill that gap and allow us to expand the possibilities of plasma application to new areas. Our previous study, related to the removal of microorganisms from the porous surface of mixed municipal waste for alternative fuel production, has also given promising results in the context of plasma applications in this area [17]. Non-equilibrium plasma helped to reduce the abundance of bacteria, mold and pathogenic microorganisms, i.e., _Enterococcus faecalis_, _Escherichia coli_, _Salmonella_ spp. and _Staphylococcus_ spp. in municipal waste. Nevertheless, this method also had its limitations resulting from the porous structure of the mixed municipal waste, its heterogeneity, higher moisture content and the presence of organic substances [17]. The exact effects of non-equilibrium plasma on microorganisms are not yet fully understood [61]. With regard to bacteria, non-equilibrium plasma most often induces morphological changes, i.e., modification of the shape of the bacterial cell. In addition, it contributes to structural disorders within the bacterial surface, as well as changes in the arrangement of organelles. Non-equilibrium plasma enhances the formation of perforations in the cell wall and thus promotes the release of cell contents to the outside, which directly leads to cell death [62; 63]. Yeast, including the _Saccharomyces cerevisiae_ species that predominates in our studies, is a traditional model eukaryotic organism used in many studies that asses cellular processes [61]. Treating yeast cells with non-equilibrium plasma induces several types of stress, resulting mainly from the presence of free radicals reacting with yeast cellular components, i.e., proteins, enzymes, genetic material and lipids. The kind of disorder caused by plasma in yeast cells impairs their basic functions, leads to disturbances of physiological and biochemical nature and eventually causes death [64]. Therefore, although the aim of the present study was to quantitatively assess the antimicrobial properties of non-equilibrium plasma, having obtained promising results in this aspect it was reasonable, as a next step, to deepen the analysis towards characterization of the mechanisms behind this process. Such a comprehensive procedure will make it possible to determine the most optimal conditions for the plasma treatment of diatomaceous earth and, ultimately, to approximate the obtained results to other microbiologically contaminated porous materials. Figure 6: pH of diatomaceous earth before and after contact with plasma.