According to the US Department of Agriculture, every year approximately 455,000 tons (412,769 tonnes) of discarded eggshells must be transported and disposed of in the US alone. Now, however, scientists at the University of Aveiro in Portugal have developed a method of using such eggshell waste in the production of ceramic goods.
Although the specifics of the technology are still under wraps, it involves incorporating crushed eggshells into a ceramic slurry which is subsequently processed "according to a specific protocol that includes a 3-cycle cooking phase." Samples of porous pavement made from the slurry exhibit desirable qualities such as porosity and water absorption, and are overall considered to be of sufficient quality to meet industry standards.
Besides keeping eggshells out of landfills, the process could also allow ceramics manufacturers to save money – the calcium in the shells would be a lower-cost alternative to calcite, which is traditionally used in the production of ceramic items. Additionally, calcite must be mined, with all the environmental consequences that doing so entails.
What's more, businesses in the food industry supplying the shells could make money by selling them to the ceramics industry, instead of spending money on having them taken away and dumped.
The process has been tested in the lab, and the university's Technology Transfer Office is now seeking industry partners to help finance a large-scale pilot project. And should ceramics manufacturers not have a need for all of the world's eggshells, scientists in India are working on a method of using them for carbon sequestration.
Source: University of Aveiro
At the time this mainly came from shell grit, crushed pieces of sea shell, but we also used to feed them some of their own crushed up egg shells.
With some reprocessing, I can't see why the shell couldn't be feed back to the chickens, mixed into their pelletised feed.
We used to use the egg eaters as roasters when I was a kid (they quickly lost their heads when they become "antisocial"/cannibalistic). Probably not an issue in the factory farming of chickens as the hen is separated from her egg as soon as it is laid.
I agree that most agricultural waste isn't actually waste (bagasse is another), the nutrients it contains either came from the soil, fossil fuels or mined at some remote location, it is far better to return the "waste" to the soil or food chain so that it can be reused, recycled, renewed.
To say that the food manufacturers don't have chickens to feed the eggs to is a blinkered thing to say, the food industry is a great big chain and the chicken feed producers should look at something like this as a resource (we aren't talking about collecting the eggshells from your garbage bin, I live in an (sub)urban environment and compost all of my green waste, including lawn clippings and there is no smell etc, sure not possible in high density housing.). The reality is, it is most likely more economical to mine the primary minerals, necessary to feed chickens (and other livestock) than to collect and process the eggshells from the custard and cake mix manufacturers to recycle it as chicken (or pig) feed. But that doesn't stop them adding; carcases, offal, feathers and miscellaneous abattoir waste to the meat meal, isn't this just another nutrient stream.
But instead, they focus on shutting everything down and going back to the stone age. They call it re-wilding. I call it crazy.