According to Insinkerator, a manufacturer of garbage disposals, "Food waste disposers can handle virtually all types of food waste, up to and including small meat bones. Meat itself, bones from poultry or fish, egg shells, fruit and most vegetables are all dealt with effortlessly." [Insinkerator]
The garbage disposal may be able to handle your eggshell waste, but your sewer lines may not fare as well.
But Eggshells Are Fragile. . .What's the Harm
It would seem that a fragile little eggshell would be easily pulverized by the mighty garbage disposal. A closer look at the anatomy of an eggshell will highlight the issue.
The eggshell is comprised of several layers. The outermost shell is made of calcium carbonate and is porous. This is covered with a protective layer called the cuticle. Directly beneath the hard outer shell, there are two strong protein membranes that protect the egg white from bacterial invasion. These membranes contain keratin, the protein found in human hair. They also have a sticky consistency, which is why they cause issues with garbage disposals. The eggshells will stick and collect and can jam a garbage disposal as well as build up on pipes and cause clogs.
Sewer Clogs Could Be a Major Expense
When you process food in your garbage disposal, it exits your house via a pipe that is either attached to a private septic tank or to a municipal sewage system. In the instance of eggshells, they can stick to your pipes, collect, and cause a clog, which can become exorbitantly costly. If you are lucky enough just to clog your garbage disposer, the cost may only be a repairman. If the clog occurs in the septic pipe somewhere between the home and the septic tank, you are likely to be facing a major expense.
Some that utilize the public sewer lines believe that issues that occur in the pipes are not their problem. Not so. Most municipalities will maintain all sewer lines UP TO the property line. Anything that occurs within the lines between your home and the edge of your property line is your responsibility. If you clog it, you incur the expense of clearing it.
A Better Use of Eggshells
Rather than sending your eggshells through the garbage disposal and risk a clog, you are better off throwing them away. Better yet, add them to the compost pile. Eggshells can be easily composted and later used as a soil amendment in vegetable or flower gardens.