## 4 Summary  
The conducted research confirms the possibility of using non-equilibrium plasma produced in a glide arc reactor for decontamination of microorganisms colonizing diatomaceous earth after the beer filtration process. Analysis of the material's porous surface with an optical microscope with 800\(\times\) magnification did not reveal any destruction of the material as a result of plasma treatment, other than its drying due to the flow of working gas. Additionally, the FTIR spectra obtained show no change in the chemical composition of the material for all treatment times (5, 10, 20, 25 and 30 min). Microbiological tests identified three types of bacteria (_Citrobacter freundii_, _Citrobacter braakii_ and _Hafnia alvei_) and three types of yeasts (_Saccharomyces cerevisiae_, _Candida spherica_ and _Rlodotula glutinis_) present in the tested material, which are associated with beer production. The effect of plasma treatment on reducing the number of listed organisms is already evident for the shortest time (5 min), and its effect increases with time. Compared with control samples, a reduction of 2.2 log\({}_{10}\) CFU\(\cdot\)g\({}^{-1}\) in the total number of bacteria and 1.72 log\({}_{10}\) CFU\(\cdot\)g\({}^{-1}\) in contaminants was observed for a time of 30 min. Although the results obtained seem very promising, more research is needed to explain the mechanisms behind the removal of microorganisms from the tested porous material. Due to the low operating costs of the system (only electricity and widely available air as a working gas are needed for operation), the authors believe that the studied system is likely to someday have practical applications in removing microorganisms colonizing diatomaceous earth after the beer filtration process by scaling up the system to a larger number of reactors operating in parallel and may also have a chance to be used with other surfaces with irregular shape and structure.  
On the basis of the performed research, the following final conclusions can be drawn:  
1. The non-equilibrium plasma generated in the mini glidearc reactor has a lethality potential against bacteria and yeast.
2. Bacteria and yeast can be effectively removed from the porous surface of diatomaceous earth using non-equilibrium plasma.
3. It is reasonable to conduct further studies to determine the possibility of removing other types of microorganisms from surfaces with irregular shape and structure.
4. Further research involving the optimization of the diatomaceous earth plasma process that leads to the complete elimination of microorganisms from its surface will contribute to its reuse in the beer filtration process as well as in other industries, i.e., cosmetology, agriculture or chemical technology.  
Conceptualization, K.W.-K. and J.P.; methodology, K.W.-K. and J.P.; validation, K.W.-K.; formal analysis, K.W.-K., J.P., T.M.K. and D.Z.; investigation, K.W.-K. and J.P.; resources, K.W.-K., M.Z. and J.P.; data curation, K.W.-K. and J.P.; writing--original draft preparation, K.W.-K., P.T., S.B. and J.P.; writing--review and editing, K.W.-K., M.Z., P.T., S.B. and J.P.; visualization, K.W.-K. and J.P.; supervision, K.W.-K. and J.P.; project administration, K.W.-K. and J.P.; funding acquisition, K.W.-K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the statutory measures of the University of Agriculture in Krakow and granted for the Department of Microbiology and Biomonitoring.  
Not applicable.  
The authors declare no conflict of interest.