Eggshell-Waste-Derived Calcium Acetate, Calcium Hydrogen Phosphate and Corresponding Eggshell Membranes

The development of innovative transformation techniques for various wastes generated by the agri-food industry is one of the goals of sustainable waste management oriented toward “zero-waste” approach. This includes the production of bulk and fine chemicals, bioactive compounds, enzymes and functional materials from various waste. The present research shows the possibility of the production of value-added products from eggshell waste using chemical transformation by acetic and o-phosphoric acid at a laboratory scale level. Eggshell-derived calcium acetate monohydrate and calcium hydrogen phosphate, both of high purity, as well as corresponding eggshell membranes as valuable by-products, were produced. Chemical transformation of 100 g of eggshell waste with 10% (w/v) acetic acid resulted in 111.41 ± 2.13 g of calcium acetate monohydrate and 2.90 ± 0.14 g of eggshell membranes, with a chemical yield in calcium acetate monohydrate of 79.16 ± 1.98%. On the other hand, the transformation of 100 g of eggshell waste in 15% (w/v) o-phosphoric acid yielded 77.06 ± 6.21 g of calcium hydrogen phosphate and 2.94 ± 0.08 g of eggshell membranes, with a chemical yield in calcium hydrogen phosphate of 71.36 ± 5.58%. Eggshell-derived calcium hydrogen phosphate met all prescribed criteria for food-grade additive, as determined by physicochemical analysis. On the other hand, calcium acetate monohydrate met the majority, except water insoluble and formic acid and oxidizable impurities content. Based on the obtained results, it can be concluded that the proposed eggshell waste transformation process by two different acids might be useful for the production of calcium acetate and calcium hydrogen phosphate as food-grade additives, as well as eggshell membranes as valuable by-products.