## 3 Results and Discussion
### Characterization of Eggshell-Waste-Derived Calcium Acetate and Calcium Hydrogen Phosphate
FTIR-ATR analysis of commercial (Figure 7a) and ESW-derived calcium acetate monohydrate of three production batches (Figure 7b) revealed an identical peak position and similar absorbance intensities attributable to the presence of symmetric and asymmetric vibration stretching of C-O bonds in acetate detected at 1602, 1528, 1446, 1416, 1028 and 670 cm\({}^{-1}\)[62]. This additionally proved that ESW-derived Ca(CH\({}_{3}\)COO)\({}_{2}\times\) H\({}_{2}\)O is of high purity, and dominantly present in monohydrate form. FTIR-ATR spectra of three independent production batches of ESW-derived calcium hydrogen phosphate (Figure 7d) and those of commercial CaHPO\({}_{4}\) anhydrous (Figure 7c), have shown identical peak positions and similar absorbance intensities of major peaks centered at 883, 983, 1058 and 1129 cm\({}^{-1}\) attributable to the symmetric stretching of P=O bonds in phosphate ion (983, 1058 cm\({}^{-1}\)), asymmetric stretching of P=O bonds in phosphate ion (1129 cm\({}^{-1}\)) and deformation vibrations of P-O-H group in hydrogen phosphate ion (883 cm\({}^{-1}\)) [63; 64; 65]. This additionally proved that ESW-derived CaHPO\({}_{4}\) is of high purity and dominantly present in anhydrous form. \begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Value** & **Food Additive Criteria 1** \\ \hline Dry matter [\%] & 99.47 \(\pm\) 0.19 & n. c. 2 \\ Calcium [\% a.w.b.] 3 & 25.64 \(\pm\) 0.68 & n. c. \\ Calcium [\% a.w.b.] 4 & 23.57 \(\pm\) 0.07 & n. c. \\ Phosphorus [\% d.w.b.] 4 & 17.25 \(\pm\) 0.20 & n. c. \\ pH of 10\% solution & 4.13 \(\pm\) 0.15 & n. c. \\ Soluble proteins [g/100 g d.w.b.] & not detected & n. c. \\ Loss on Drying [\%] & 1.40 \(\pm\) 0.16 & \textless{}2 \\ Loss on Incineration [\%] & 8.43 \(\pm\) 0.31 & \textless{}8.5 (anhydrous) \\  & & \textless{}26.5 (dihydrorate) \\ Fluoride [mg/kg] & \textless{}10 & \textless{}50 \\ As [mg/kg] & \textless{}0.36 & \textless{}1 \\ Cd [mg/kg] & \textless{}0.04 & \textless{}1 \\ Pb [mg/kg] & \textless{}1 & \textless{}1 \\ Hg [mg/kg] & \textless{}0.01 & \textless{}1 \\ Al [mg/kg] & \textless{}26.99 & \textless{}80 \\ \hline \end{tabular} 1  
\end{table} 
Table 4: Physicochemical Analysis of Eggshell-Derived Calcium Hydrogen Phosphate. Based on all that was aforementioned, it should be clearly stated that the proposed ESW transformation process using 10% (\(w/v\)) acetic and 15% (\(w/v\)) \(o\)-phosphoric acid shows a great potential to be used for the subsequent production of corresponding calcium salts and eggshell membranes. The ESW chemical transformation using 10% (\(w/v\)) acetic and 15% (\(w/v\)) \(o\)-phosphoric acid yielded 111.41 \(\pm\) 2.13 g of calcium acetate monohydrate and 2.90 \(\pm\) 0.14 g of eggshell membranes per 100 g of ESW containing \(\sim\)85% dry matter, and 77.06 \(\pm\) 6.21 g of calcium hydrogen phosphate and 2.94 \(\pm\) 0.08 g of ESM (Table 1). While the yield of the produced calcium acetate monohydrate and calcium hydrogen phosphate (Table 1) was quite satisfactory, question remains whether omitting the step of neutralization of the excess of 10% (\(w/v\)) acetic and 15% (\(w/v\)) \(o\)-phosphoric acid, previously reported by our research group for the production of ESW-derived calcium chloride using 5% (\(w/v\)) hydrochloric acid [1], was the right choice, but this is a question which should be addressed in the future research. The obtained Ca(CH\({}_{3}\)COO)\({}_{2}\)\(\times\) H\({}_{2}\)O and CaHPO\({}_{4}\) salts were white (Figure 6) and their FTIR-ATR spectra (Figure 7) were identical to the commercial calcium acetate monohydrate and calcium hydrogen phosphate anhydride which indicated their high purity. Figure 7: FTIR-ATR Spectra of Eggshell Derived and Commercial Calcium Acetate Monohydrate and Calcium Hydrogen Phosphate. (**a**) FTIR-ATR spectra of Commercial Calcium Acetate Monohydrate; (**b**) FTIR-ATR Spectra of Eggshell-Derived Calcium Acetate; (**c**) FTIR-ATR spectra of Commercial Calcium Hydrogen Phosphate Anhydroous; (**d**) FTIR-ATR Spectra of Eggshell-Derived Calcium Hydrogen Phosphate.