## 4 Conclusions  
The conducted research revealed that the _K. xylinus_ K2G30 strain was characterized by the highest efficiency for BC production in both the classical and waste media. Based on the results, it can be concluded that the _Ga. hansenii_ strain exhibited greater BC biosynthesis in the waste media of a plant origin (banana peels, celery pomace, hemp pomace) compared with the waste of an animal origin (fish waste and acid whey). On the contrary, the _K. xylinus_ strain produced more BC in the medium of an animal origin (fish waste and acid whey) compared with the plant origin media. For both strains of _Ga. hansenii_ and _K. xylinus_, a trend was noted that the type of waste was more important for BC biosynthesis than its concentration. The only differences between concentrations within the same waste were noted in banana peels and celery pomace media for both strains. However, AW with a concentration of 70 g\(\cdot\)dm\({}^{-3}\) was recognised as the best waste medium for BC obtained by _K. xylinus_. In truth, there were no significant differences between AW concentrations; from an economic point of view, choosing a concentration of 20 g\(\cdot\)dm\({}^{-3}\) would be suggested. However, the highest mass of BC was obtained at a concentration of 70 g\(\cdot\)dm\({}^{-3}\). In addition, it is worth noting that AW was reconstituted from powder and a concentration of 70 g\(\cdot\)dm\({}^{-3}\) was most similar to the unprocessed liquid AW sourced directly from industry. The use of such AW would be the most preferable because it would eliminate the AW powdering process, which could reduce the cost for obtaining BC.  
In the second stage of this study, we attempted to modify the medium with AW through deproteinization. Importantly, AW deproteinization did not affect the structure of BC, which was confirmed by the analysis of the FTIR spectra. However, it was found that non-deproteinized AW was characterized by the most appropriate composition for BC biosynthesis compared with the deproteinized media. On such grounds, it may be concluded that the presence of whey proteins positively influenced the BC biosynthesis. These results also confirm the validity of using unprocessed AW for BC biosynthesis and reducing the cost of the process. Interestingly, in the case of the AW medium where the mass of BC was the highest, a considerable decrease in lactic acid content was noted. This creates opportunities to expand on research regarding BC biosynthesis in AW, with particular emphasis on the impact of lactic acid. Despite the above results, it should be remembered that the efficiency of BC biosynthesis in AW was definitely lower than in the classic YPM medium. Therefore, in order to improve the efficiency of BC production in AW, while keeping costs as low as possible, further research should be conducted.  
Conceptualization, J.P. and L.S.-R.; investigation, J.P., S.K. and L.S.-R.; methodology, J.P. and L.S.-R.; supervision, L.S.-R.; writing--original draft, J.P.; writing--review and editing, J.P., M.G. and L.S.-R. All authors have read and agreed to the published version of the manuscript.  
Funding: Part of the research (FTIR analysis) was conducted during a [PERSON] scholarship funded by the Polish National Agency of Academic Exchange (NAWA) program for students and scientists as part of bilateral cooperation, No. BPN/BIL/2021/1/00171/U/00001. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.