If you have chickens & if you eat eggs then why buy calcium supplements for your flock?
You can reduce the carbon footprint by reducing your personal waste, manufacturing waste, and reduce the amount of money you spend on buying calcium supplements by feeding your hen's eggshells back to them.
This is what I do.
I bake my eggshells in the toaster oven for about 10 minutes (or oven if it is already in use) till they are dry (usually at about 350 degrees). This is done to kill any pathogens and dry them out to help prevent pathogens from forming on them in storage. I don't rinse my shells before baking. I personally see it as a waste of time and water since the baking process dries out what little is left of the egg whites.
Be careful not to bake too long or hot. If they start to brown and burn, the smell is horrible.
I store as many baked shells as I can in an egg carton until I have a full case.
Then, I crunch them and put them in the food processor.
Grind them up into teeny tiny pieces.
This helps break them down into a powdery grit.
This, along with the baking will keep your hens from associating this part of their feed with their own eggs.
I mix them in with the feed. They wont eat it if they don't want to. Some days there are more eggshell bits left in their feeder than other days.
Others folks give them separate as free choice.
This page (as with all my other postings) are not meant for medical or veterinary advise! These are just to share my experiences. Hope it helps.
I am limited on counter space so...
When some parm cheese and truvia containers became empty I was struck with a re-use idea.
I toaster bake the shells immediately. Let cool. Lightly crush with hand and put in the parm container. when that one is full, I process and store in the truvua container. Neater and less space used.