## 1 Introduction  
The use of diatomaceous earth in beer filtration is considered one of the fifty most important technological achievements in brewing of past years [1]. This is because diatomaceous earth is characterized by a unique porosity and high adsorption capacity, as well as a low density [2]. Thanks to that, it possible to achieve high beer clarity with relatively low auxiliary material costs. After properly conducted cold conditioning, lager beer is clear; however, to ensure a higher level of clarity and stability, filtration is necessary. Diatomaceous earth deposits were formed by the deposition of ancient marine algae (diatoms), mainly in the present-day USA and China. Its global production in 2013 was 2.3 Mt, of which more than 30% was extracted in the USA, about 20% was in China and 14% was in Denmark; the rest was extracted in 26 other countries [3]. It is thought that about two-thirds of its total extraction is used for beverage (mainly beer) filtration purposes [4]. In order to obtain a clear beer, it is recommended to use 1 to 2 g of this rock per liter of clear product. However, after the filtration stage, the mass of spent diatomaceous earth is significantly higher than the original mass. This is because some of the water and other organic components (yeast, proteins, and polyphenols) are retained with it on the filter barrier [4; 5]. For a medium-sized brewery, the amount of spent diatomaceous earth with sludge generated annually is around 100 tones [6]. As a result, along with spent grains, residual yeasts and truly, it represents the main brewing waste. Its consumption could be reduced by using other, often expensive, filtration materials or by promoting the consumption of cloudy, unfiltered beer. Such a procedure would be uneconomical or difficult to implement, especially for large beer producers whose consumers expect beer with very high clarity [5]. The environmental consequences of producing such large quantities of spent diatomaceous earth are not yet well understood. The main part of the diatomaceous earth used for filtration is still stored or used as fertilizer [2; 7]. The current trend of reducing generated waste and finding alternative ways to manage it is one of the priorities for food production plants. In addition, some scientific centers work on finding alternative ways to use diatomaceous earth. Preliminary research aimed at using diatomaceous earth in the production of cost-effective biosorbents [7], storage pest control agents [8], brick production [9; 10; 11] and silver nanocomposites [6] seem to be interesting solutions in this regard. The multiple possibilities of using plasma result from the fact that numerous active agents are generated during its operation, which can affect the treated material in different ways and change its physicochemical properties. Consequently, the scope of potential applications of plasma in material technologies is constantly expanding: from cleaning and simple changes in wettability and surface micro-roughness to chemical and structural modifications, removal or deposition of layers and the formation of anti-corrosion coatings or coatings with other specific properties that protect against gas diffusion, high temperatures, excessive wear, etc. [12; 13; 14]. Other possible applications are based on the strong antimicrobial effect of plasma, as it generates reactive oxygen and nitrogen forms, i.e., hydrogen peroxide, OH, OH\({}_{2}\), NO, O\({}_{3}\) radicals, etc. A very important, additional antimicrobial factor is UV radiation, which is generated during plasma treatment [15; 16; 17]. The effect of plasma on microorganisms is multistage. The most common are: irreversible damage to the cell wall, disruption of the function of the cytoplasmic membrane and cell organelles, and damage to the genetic material [15]. In general, medical technologies use plasma, e.g., for disinfection and stimulation and in anti-cancer therapies, wound healing and theranostics [18; 19; 20].