## 3 Results and Discussion
### Eggshell Waste Transformation using 10% Acetic and 15% o-Phosphoric Acid
Moreover, it should be pointed out that none of the aforementioned authors perform the simultaneous production of Ca-acetate and corresponding ESMs from eggshell waste. Numerous reports deal with the transformation of ESW using _o_-phosphoric acid [2, 8, 10, 13, 27, 28, 29, 30, 31, 32, 33, 34, 35], but the possibility of the production of calcium hydrogen phosphate from ESW has been reported by only one scientific report [42] and one patent [56]. [PERSON] et al. [42] prepared calcium hydrogen phosphate of high purity/yield of 99.63% using ESW, which is much higher than the mass yield observed in our research (77.06 \(\pm\) 6.21%), but authors used an ESW calcination at 500 \({}^{\circ}\)C for two hours where all organic matter was incinerated, and a much greater _o_-phosphoric concentration (50%) for the solvation of ESW calcium carbonate. [PERSON] and [PERSON] [56], in their patent, used 85% _o_-phosphoric acid diluted with water in a ratio of 1:2, where ESW-derived foam obtained during the transformation process was dried in order to obtain calcium hydrogen phosphate with an approximate yield of 94% per dry matter. While both aforementioned reports clearly achieved a greater yield in calcium hydrogen phosphate than that observed in our research (-77%), it should be pointed out that the authors did not perform the simultaneous production of calcium hydrogen phosphate and corresponding ESM. Moreover, authors \begin{table}
\begin{tabular}{c c c} \hline \hline
**Eggshell-Waste-Derived Product** & **Mass Yield** & **Chemical Yield** \\  & **[g/100 g ESW]1,2** & **[\%]** \\ \hline
10\% (\(w/v\)) acetic-acid-derived ESM & 2.90 \(\pm\) 0.14 & n. a. 3  \\
15\% (\(w/v\)) _o_-phosphoric-acid-derived ESM & 2.94 \(\pm\) 0.08 & n. a. 3  \\ ESW-derived Calcium Acetate Monohydrate & 111.41 \(\pm\) 2.13 & 79.16 \(\pm\) 1.18 4  \\ ESW-derived Calcium Hydrogen Phosphate & 77.06 \(\pm\) 6.21 & 71.36 \(\pm\) 5.58 5  \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The Yield of Eggshell Membranes, Calcium Acetate and Calcium Hydrogen Phosphate Produced from Eggshell Waste. used a much higher \(o\)-phosphoric acid percentage for ESW transformation than that used in our research (50% or \(\sim\)30%, contrary to 15% used in our research), and in the case of [PERSON] et al. [42] an energetically demanding process of ESW calcination at 500 \({}^{\circ}\)C was used. The production of ESMs from ESW using 10% (\(w/v\)) acetic and 15% (\(w/v\)) \(o\)-phosphoric acid transformation process (Figure 2) resulted in a similar mass yield of 2.90 \(\pm\) 0.14 and 2.94 \(\pm\) 0.08 g per 100 g of ESM (Table 1). The obtained results were in accordance with our previous report [1], where 2.84 \(\pm\) 0.16 g of ESM per 100 g of originally used ESW was obtained using a 5% (\(w/v\)) hydrochloric acid treatment of ESW, but were lower than those reported in the patent of [PERSON] [57], where an ESM yield of 6 to 10% per ESW was obtained by ESW mechanical treatment, including milling and sieving. Since data on the possibility of ESW utilization using 10% (\(w/v\)) acetic and 15% (\(w/v\)) \(o\)-phosphoric acid (Table 1) clearly showed that the proposed process of ESW utilization (Figure 2) has a great potential to be used for the production of calcium salts and ESMs, it was necessary to characterize the obtained ESMs and derived calcium salts.