Everybody poops.
WASH ROOMS
No bathrooms or kitchens in the commoner homes, you're wondering, where do people take a shit, or get water? Ever notice that the top layers go unused, but have pillars going up to it? That's right. Above all domes are major wash rooms, with thousands of pots to take thine dumps on. Multiple chambered levels hold large scale units of public baths.
Outer structure needs minimal piping that guides down waste by pure physics through copper-lined (read: anti-microbial) chambers with Fairy Smoke (read Agriculture) and Archaea deposits for cleansing of bacteria, general enzyme treatment, and removal of volatile gasses. More classic filtration systems are also in use en route such as copper and hopcalite (copper and manganese) filters. Hopcalite is a method of converting carbon monoxide to carbon dioxide, remove ethylene oxide, other volatile organic compounds, ozone from gas streams, and are commonly used in air filtration systems like scuba diving and firefighting, and is the main filtration ingredient in rescue respirators for miners. Treated solid wastes drain into Unazhaal basin levels to begin composting processes (before ultimately dropping further), while liquid properties drain off more classic channels and essentially drop into other chambers. The urine, once heat-treated for extra precaution (despite being more sterile than most water, it's the thought), it's used for...
Metal treating, Ammonia creation, leather generation, Saltpetre/Gunpowder components manufactured from/into potassium nitrate. Electricity generation (it's complicated just... just look it up. One liter of urine, six hours of electricity. You'll find it... This is particularly useful as there's very little electrical use in the world and between this and the mills, it self functions.) Reduction to Phosphorus, for weaponization and export.
Archaea are organisms closely related to bacteria, which proliferate in cave-like conditions. They're not infectious, they're enzyme sources that endure extreme conditions for things like molecular biology and long story short, have use in cloning DNA. Other Archaea are great for food processing at high temperatures for specifics, for things like low lactose milk and whey. They're stable organic solvents that make environmentally friendly processes and green chemistry to synthesize organic compounds. They are, however, a vital part of sewage treatment. Not only is it harvested for prior uses, it is an integral part of the purification process for the sewage and composting. Ironically, it's also used for extracting metal from ores including gold, cobalt and copper, while converting biogasses that other parts of the system haven't, and actually recycle into breathable compounds. So not only does it assist in the mining, and air, they literally sift gold from layers of poo over time. It's very gradual, but it happens.
Certain crops are grown at vent points for final pieces of the process. Don't freak. Most of your real food touches fertilizer at some point, too.
Go organic!
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