## 1 Introduction  
Linear economics has underpinned the current growth in the world's population. Indeed, in the space of five decades, there has been an increase from 2.5 to 7.9 billion people, justified by the environmental capacity and resources [1]. Using natural resources and primary energy without considering alternatives is defined as linear economics. This approach is, however, the major contributor to the consumption and draining of natural sources, ultimately flowing into the severe environmental, economic, and social crisis the world is currently facing [1]. If linear economy depletes resources, circular economy instead implements environmental sustainability by encouraging resource reuse and recycling [2]. This perspective decreases both human impact and pollution derived from the waste [3]. A particularly noteworthy field of application for circular bioeconomy is scientific research, yielding a circular bioeconomy [4] where sustainable products are generated from biological wastes, mostly from food, industrial, and agricultural sources [3]. The exploitation of food wastes was for a long time as feed additives for animals [5]. Recently, other applications arose. For instance, biorefineries started exploiting wastes to produce natural renewable gas [6], and textile sector relied more on natural dyes, such as pomegranate seeds, for tissue staining [7]. _Castana sativa_, known in Europe as sweet chestnut, is economically valuable for its nutrient-rich fruit, the chestnuts. Their abundance in carbohydrates, fibers, starch, fatty acids, minerals (potassium, phosphorous, calcium, and magnesium), and vitamins (B9, C, and E) [8; 9; 10; 11; 12] valorizes them in a Mediterranean diet [8; 13] and for treating illnesses like diarrhea and cough [12]. The nuts are encased in a hard, spiky shell, and a typical glossy brown nut with a pointed tip is found within the husk. When cooked, chestnuts have a starchy and unique sweet flavor, and lower oil content compared to other nuts [14]. Interest in chestnut production is currently rising, especially in Spain, France, Brazil, the USA, and Switzerland, holding the lead in chestnut exportation rate (77.6%) [15]. Despite the relevance of _C. sativa_ as a fruit crop, its bark in particular is used to extract tannins (vescalgin, castalin, and vescalin) and it accounts for 60% of the total amount of tannic substances [12]. Several studies have shown that chestnuts are rich in tannins in the bark and leaves; furthermore, chestnut byproducts (like the burr) represent a source of biomolecules with antioxidant, anticarcinogenic, and cardioprotective activity [11]. Burrs must be removed from the brush woods to ensure optimal growth of the tree (usually by burning them), causing damage in terms of time and financial resources. This practice is not only dangerous, but it also contributes to environmental pollution by releasing carbon dioxide. From this perspective, the interest in a more sustainable chestnut exploitation process rose. Previous research already exploited chestnut shells to withhold pollutants from the environment, to produce energy through carbon combustion, and to generate active carbons as adsorbent molecules [16]. Another current application of agri-food wastes, mainly crop residues, sees them a source of various bioactive molecules. For instance, coffee husks are a count of phenolic compounds, notoriously displaying antioxidant activity [1]. In the chestnut burrs of _C. sativa_ particularly abundant is ellagic acid with antioxidant properties, as well as an antimicrobial effect against _Helicobacter pylori_[17]. _Enterococcus faecalis_ is a Gram-positive bacterium able to cause hospital-acquired infections (HAI), urinary tract infections (UTIs), bacteremia, valve endocarditis, and wound infections [18; 19]. Currently, endocarditis, bacteremia, and UTI treatments are represented by combination therapy, consisting of the coadministration of cell wall-active agents, such as \(\beta\)-lactams, and aminoglycosoides [19]. However, _E.