Oh, well that’s nutritious and high in fiber. I’m sure Bob’s using the solid wastes in some manner that’s positive, but not to be thought about too closely.
Possibly.
Best not to think of it.
Oh, he's told us about it already. It's in the small review of the Castle:
In space, everything gets recycled.
We know this, but we don't think about it. Prior to taking off for space, we had to think about it.
We had an advantage. We were designing systems that would never have to operate in zero-gee. At least, we hoped so! If we didn't have either thrust or rotation, a non-functioning toilet would be the least of our problems.
The Castle would literally come apart. Our apparent gravity keeps things in place, and our systems were designed to work that way.
So just like terrestrial systems, our water reclamation works by gravity, pumps, and filters. Like systems that were designed a hundred years ago, the first stage involves separation, settling, and the addition of chemicals to speed the process.
In the Castle Habitat, there is an additional stage of biological filtration and separation that is not available on A and B. Their systems are purely mechanical and energy intensive. (At least we have nuclear energy, so don't worry!)
The Castle system takes advantage of the swampy area to the left of the main Castle gate. Treated water which has not reached its final filtration level is released into that ecology to nurture the wild plants. You will notice that they are thriving, just as Irma Bombeck predicted.
It is important that we do this, as there is no other way that a natural ecology could be sustained. Many small creatures depend upon that ecosystem, as confined as it is. From frogs and snails to lizards and songbirds, the nutrients move up the food chain. It is a safety valve for us, and we monitor the health of these organisms.
Most of the rest of the natural world we have captured here is watered by the nearly continuous condensation that occurs on our transparent canopy. The forest and meadows are satisfied with this because they have other methods of getting nitrogen for example. Eventually we may need to take more direct measures, but for now the systems maintain themselves fairly well.
Aquifer collection stations rim the exterior of the Castle Habitat, where naturally filtered water is then mechanically filtered, checked for pathogens and contaminants, and then resupplied for consumption. The entire Flying Castle Habitat is a functioning still for producing clean water!
The separated solids are returned to productive use by a system of double biological separation. First they are tilled into special fields by machines which blend them in like kneaded dough. Selected grasses are sown and eventually harvested.
The collected grasses are then tilled into regular fields as so-called "green manure", meaning pure biological material that is intended to fertilize a second tier of crops.
This is the material that brings the nutrients back to our pastures and orchards. In several stages, possible contaminants are separated out for more intensive treatment.
Metals, for example, are separated in a variety of ways to be recycled in the forges and kilns of our factory levels.