A literature review on adding value to solid residues: egg shells.

The production of chicken eggs on an industrial level leads to a considerable quantity of shell residue, which is considered as a waste or is used as a complement in agriculture. In general, egg shells are considered to have no economic value, even though they are rich in minerals and amino acids that could form the basis of several industries. In this study, information was reviewed on the technological potential for usage of the minerals and protein membranes of the egg shells. Possible applications range from low investment processes such as fertilizer and animal feed to high investment for transforming as the material for human consumption, absorption of heavy metals, paper treatment, catalysts for biodiesel production, production of hydrolyzed or concentrated protein, bone and dental implants. The last applications need large investments but can provide more valuable products. Based on this literature review, process alternatives and their estimated environmental impacts are considered as a preliminary study with a view to the development of industrial plants, which can use egg shell residues, in order to add value by using these materials in environmentally safe ways. In general, all processes suggested in this paper present high environmental and economic benefits.