Eggs shells don’t work unless they’re ground into a very fine powder.

I don’t know the answer to this question. You may be right. And yea, I can see limestone in the right doses working.

And we could always extract the nutrients from our waste. Close the cycle: what goes in, goes out. We’re already using biosolids in agriculture.

This thread is weird. It seems like you all never heard of compost.

Okay, concerning 2 I thought you meant, why count and buy exactly this number. But it’s actually realistic, for a big family, or for desserts for a party, etc.

I think 2 and 3 are the same problem.