To safely compost eggshells, you can either heat the shells in your oven to kill bacteria, or practice safe composting to kill the bacteria by cooking the eggs in your pile. To bake them yourself, arrange the eggshells on a baking tray and cook them for 25 minutes at 240 degrees Fahrenheit, which kills even the most potent form of this bacteria.
Eggshells are high in calcium. Adding them to your compost pile enriches your compost, which can in turn give the nutrient to your garden soil when you work it in. Composting also reduces your waste and environmental impact.
Not only do eggshells decompose slowly, but passively tossing the shells onto your pile won't ensure the bacteria dies. To help break them down -- whether you prebaked them or are relying on heat to kill them -- you can crush the shells into small pieces before adding them. If you don't have the time to monitor the compost pile, you may not want to compost your eggshells.
If you generate enough heat from your home compost pile, or if you have an automatic composter -- these generate high heat -- you can compost eggshells without worrying about salmonella. To nix the bacteria, you need to raise the heat above 130 degrees Fahrenheit, the limit of most backyard compost piles. You can monitor the heat of your pile with a thermometer, and raise the compost temperature by composting one-third nitrogen-rich materials and two-thirds carbon-rich materials, and by turning the pile once a week to aerate it.