Egg shells waste management

To begin, we have to know the avian egg from inside out. It consists of:

• The egg yolk made up of a number of spherical compartments. Unlike the egg white, which contains very little fat, the yolk contains a significant amount of fatty acids such as oleic acid, palmitic acid, and linoleic acid, as well as high level of cholesterol. It also contains fat soluble vitamins (A, D, E, and K).

• The egg white/albumen that is 90% water. One of the most important proteins in the albumen in terms of the egg white’s consistency is ovomucin which helps to thicken the egg white and give it its gloopy consistency.

• The egg shell membrane primarily composed of fibrous proteins such as collagen type I. Eggshell membranes also contain glycosaminoglycans. 

• The egg’s shell is made primarily from calcium carbonate, the chemical compound which also makes up the majority of sea shells, as well as chalk and limestone. 

Egg shell waste was estimated to be at 2.3 million tonnes worldwide in 2018. The food industry is the one that uses most eggs hence contributing to this pollution. When egg shells, egg shell membrane and egg white decompose it leads to production of ammonia(NH₃) and Hydrogen sulfide (H₂S) with an offensive odor that attracts insects and rodents. People have been finding ways to curb this pollution by finding solutions. Many patents have been submitted in recent years about how to recycle this waste and techniques used to make it into powder form.

Many applications have been discovered, they include in areas such as medicine, steel manufacturing, building and construction, water treatment, agriculture, paper and pulp, plastics, and paint.

The paper industry uses limestone-based raw material to produce fillers and coating pigments, such as Calcium carbonate(CaCO₃ ) pigment for printing paper and board.

Egg shells showed potential as a replacement for limestone to prepare hydroxyapatite (HAP) utilized for the sustainable treatment of toxic metal-polluted water.

In medicine, the hydroxyapatite is also used in medicine for bone repair and tissue regeneration as it is a major component in teeth and bones. The bone is made up of (Ca₁₀(PO₄)₆(OH)₂HAp) and collagen fibers. Egg shell is also an acceptable source of calcium supplement for animal feed and human health since use of shrimp and oysters will not be ecologically possible in the near future.

They can also be used as fertilizers by being converted to liquid calcium acetate fertilizer via the reaction of pulverized ES with acetic acid. Calcium carbonate fertilizers have low solubility hence unsatisfactory intake but calcium acetate is relatively neutral (0.2 M solution is pH 7.6), it does not acidify soil when used as an amendment. 

They can also be used as a biodiesel catalyst since it is renewable, biodegradable, non-toxic and has low emissions.

More information on how to reduce egg shell pollution:

https://www.frontiersin.org/articles/10.3389/fbioe.2021.675364/full

30+ Things to Do with Eggshells

https://www.sciencedirect.com/science/article/abs/pii/S0921344916302750

https://www.linkedin.com/pulse/10-great-uses-eggshell-powder-derek-tower