I grew beans in a window box (roughly 0.4x0.4x2m) a few years back. They do indeed grow very well, but my problem was that they covered half the window bars and blocked out the light to the other plants. D’oh!
I had a moringa tree growing at one end of the box. It did fine, but never produced any ‘beans’. That was a bit of a waste of space because although I like the leaves in small doses, it produced way more than I wanted to eat.
Okra probably would have been a good bet, but I don’t much like okra. Sweet potatoes, definitely.
If we really had to grow our own food, I don’t see any option other than getting auxiliary lighting set up. Without it, you don’t have enough square footage, and it’s too complicated to work around the available sunlight. With careful choice of crops you could probably get 5m2 crammed vertically into an average balcony, producing maybe 50-70kg of food over the course of a year. If you had enough money to add fat and protein from animal products, that’d be enough to keep one person healthy. You’d want to ferment all your scraps and put them back into the growbeds.
A compact freeze-dryer is a great idea - I was actually looking for a product like this a few years back - but I’m not sure that food waste is the underlying problem here. How on earth does food waste generate “soil contamination” or water pollution? That makes no sense at all. It’s more likely to be due to the sort of behaviour that @Explant flagged up last week - plastic waste, burning trash, etc.
Returning food waste (I mean genuine food waste, like peelings, trimmings, and inedible stuff) back to the soil is exactly what you want to happen. But it needs to happen much more efficiently than it does now. Freeze drying is great for food preservation for the off-season, which reduces sales bottlenecks during production gluts.