https://arstechnica.com/science/2023/09/dont-throw-out-those-used-coffee-grounds-use-them-for-3d-printing-instead/
Any object you create can be thrown back into a coffee grinder and reused on a new object.
This was the info I was interested in.
Finely ground (espresso) coffee grounds were dried in the sun and then sifted. Then mixed with binders (xanthan gum and carboxymethyl cellulose powders) and water. These are printed in a modified consumer grade fdm 3d printer using a syringe instead of the hot end. The resulting material is claimed to be as strong as unreinforced concrete, but is biodegradable.
I’d be curious what their measure of concrete is. The plain stuff has 3000psi compressive strength and a usable modulus of rupture of around 250psi. And if it survives re-wetting / over-drying and aging.
PLA is (very) roughly 20x that.