Waste & the Reactor

Human waste never enters a mixed-waste plant in this design — it’s sorted before it ever leaves the room. Each of 144 bath-and-entry units per building has its own micronising pressure toilet, grinding solids into a slurry right at the fixture. Recyclables go up whole to the scrap trade; food scraps go to farms, worm beds, and livestock. None of it touches the reactor. Only human waste does, already reduced to a uniform, pumpable stream before the building’s mechanical systems ever see it.

That slurry feeds a coiled tube reactor running supercritical water gasification — not pyrolysis, and not incineration. Pushed past water’s critical point (374°C, 22.1 MPa) into 600–700°C and 25–30 MPa, water stops behaving like a liquid or a gas and becomes both solvent and reactant at once. Organic material breaks down chemically in the water itself, with no drying step required — which matters, because drying a wet feed is the single largest energy cost in every competing waste-to-energy route. A thousand people produce just 0.20 kg of dry solids a day each, a fifth of an ordinary town’s rate, thanks to bulk buying and stripped packaging elsewhere in the design.

The reactor itself is small: 900 metres of 21mm tube, coiled into roughly a third of a cubic metre, giving 15 minutes at reaction temperature. Output splits 85–90% into a methane-rich gas that feeds the fuel cell’s anode directly (see Energy & Power), with up to 10% coming out as solid char. Heat to reach operating temperature comes mostly from the fuel cell’s own flue gas — the two systems run in a closed loop, each supplying what the other needs.

Where the design has a real, acknowledged hole

Getting the slurry into the reactor at 300 bar, with solids still suspended in the stream, needs a pump that does not currently exist as a catalogue product. High-pressure pumps built for clean fluids run at ten times this flow; pumps built for abrasive solids top out well below 300 bar. One manufacturer’s unit meets both specs, but its smallest size is 24 times larger than what this reactor needs. The fallback is a custom-built pump — priced at $275,000 with a 39-week lead time — and that price is itself explicitly labeled a guess, extrapolated from similar custom equipment rather than quoted by anyone who’s built this part. A second, related gap sits on the outlet side: no valve exists rated to survive 650°C, 300 bar, and precipitating salt all at once, so the design instead quenches and lets the stream down cold, in stages, running parallel trains so one can be serviced without stopping the reactor.

Governed by Bureau 23.