## 3 Results and Discussion
### Microbiological Analysis  
Microbiological analysis revealed that spent diatomaceous earth after beer filtration was populated by two groups of microorganisms: bacteria and yeast. The obtained results are consistent with the available literature data, stating that, due to its porous structure, during the filtration process diatomaceous earth retains the yeast used in beer production on its surface, as well as a few bacteria that get into the solution during routine technological work [54; 55]. No other groups of analyzed microorganisms were found in spent diatomaceous earth. Species identification of the isolated bacteria and yeasts using the MALDI-TOF MS technique allowed us to determine the following three bacterial species (\(n=155\)): _Citrobacter freundii_ (\(n=90\)), _Citrobacter braakii_ (\(n=55\)) and _Hafnia alvei_ (\(n=10\)) and three species of yeast (\(n=320\)): _Saccharomyces cerevisiae_ (\(n=300\)), _Candida spherica_ (\(n=10\)) and _Rlodotati glutinis_ (\(n=10\)). Based on the test results shown in Figure 5, it should be concluded that the non-equilibrium plasma has a strong lethal property against the tested bacteria and yeast. In the control sample, not subjected to plasma treatment, the following levels of bacteria and yeasts were found: 635,760 (CFU\(\cdot\)g\({}^{-1}\) D.M.) and 1,046,722 (CFU\(\cdot\)g\({}^{-1}\) D.M. ), respectively. It was clearly visible in the plasma-treated samples that the number of microorganisms decreased with the increasing contact time of diatomaceous earth with plasma. The best results were obtained after 30 min of plasma treatment, as bacterial and yeast counts dropped to 2461 and 42,033 (CFU\(\cdot\)g\({}^{-1}\) D.M. ), respectively. However, even at shorter contact times the plasma worked effectively. A large decrease in the number of bacteria was observed after 10 min of plasma treatment of diatomaceous earth and amounted to 120,707 (CFU\(\cdot\)g\({}^{-1}\) D.M.). In the case of yeast, successive count decreases were more evenly distributed and proportional to the plasma treatment time. Analysis of the obtained results showed that the log\({}_{10}\) reduction of bacteria relative to the control was as follows: 0.86  
Figure 4: FTIR spectra for the control sample and the 30 min plasma treatment. (P5), 1.15 (P10), 1.92 (P20), 2.05 (P25) and 2.20 (P30). In contrast, the log\({}_{10}\) reduction of yeasts was: 0.64 (P5), 1.11 (P10), 1.2 (P20), 1.3 (P25) and 1.72 (P30). The lethal properties of non-equilibrium plasma against bacteria and yeasts were also confirmed by other authors [56; 57; 58]. [PERSON] et al. [56] found a 31-89% decrease in _E. coli_ (depending on the strain) in plasma-treated air. [PERSON] et al. [57] observed 100% elimination of multidrug-resistant strains of _Salmonella enterica_ after just 5 min of plasma treatment. On the other hand, [PERSON] et al. [58] examined the effect of environmental factors on the survival of _S. cerevisiae_ yeast cells placed in two solutions: water and saline. Their study revealed that yeast cells treated with plasma in water underwent the most severe morphological and physiological damage, including damage to membrane lipids and genomic DNA. _S. cerevisiae_ cells treated with plasma in saline were much less damaged. The shares of yeast cells that survived plasma treatment were 80% and 40% for saline and water, respectively. [PERSON] et al. [58] concluded that this was due to the protective role of saline against yeast, weakening the effect of free radicals. [PERSON] et al. [59], during their study on plasma treatment of _Candida albicans_ yeast in an aqueous suspension, obtained even better results because the number of cells that survived the process dropped dramatically from 5 \(\times\) 10\({}^{4}\) CFU/mL to zero after just 6 min of contact with plasma. As the examples above show, it is clear that non-equilibrium plasma can be used to eliminate microorganisms from various sources.