The system
Three stages and two couplings. The couplings are the point; without them this is three separate inventions rather than one machine.
Stage 1 — Bioremediation
Regolith enters a sealed, humid, anaerobic chamber inoculated with perchlorate-reducing bacteria. They use perchlorate as terminal electron acceptor and leave inert chloride behind:
ClO₄⁻ → ClO₃⁻ → ClO₂⁻ → Cl⁻ + O₂
The route runs through perchlorate reductase and chlorite dismutase. The strains are Azospira suillum PS, grown in the laboratory at 37 °C, and Dechloromonas aromatica RCB, a soil microbe. Neither is engineered.
Do not oversell the oxygen
The O₂ in that equation is respired by the same cells. Even if all of it were captured, six crew would need 1.7–4.2 tonnes of regolith treated every day to breathe from it. The benefit of this stage is detoxification.
Stage 2 — Filtration column
Treated regolith and biochar are layered in a column. Greywater is applied at the top and percolates down under gravity. The biochar adsorbs metals and dissolved organic load; the regolith retains suspended solids.
| Layer | Depth | Function |
|---|---|---|
| Coarse regolith | 50 mm | distributes flow, prevents channelling |
| Fine regolith | 200 mm | retains suspended solids |
| Biochar | 120 mm | adsorbs metals and dissolved organics |
| Support gravel | 50 mm | drainage |
The effluent reaches the main water processor with reduced load, so it works less and its membranes last longer. This is the stage built and tested on the bench.
Stage 3 — Pyrolysis
Food waste and paper are heated to around 500 °C without oxygen. The material does not burn, it chars. Slow pyrolysis leaves about a quarter of the feed as char, and that char adsorbs metals and organics from water.
What makes it one system
Stage 3 supplies two things Stage 1 cannot operate without on Mars.
| Coupling | Why it is needed |
|---|---|
| Waste heat | The retort runs near 500 °C. The reference strain grows at 37 °C, and the Martian surface falls to about −153 °C. Retort heat is routed to the bioreactor jacket; the retort needs 5.0–7.6 MJ a day for six crew, and how much of it reaches the jacket is still open. |
| Electron donor | The bacteria need an organic donor such as acetate or lactate to respire perchlorate. Supplying it from the pyrolysis liquid is the target; until that is shown, the donor is a consumable. |
Remove Stage 3 and Stage 1 loses its heat and, eventually, its donor. Remove Stage 1 and the regolith stays toxic and cannot serve as filter medium.
Open design question
With the stages stacked, gravity helps twice and hinders once:
- Treated regolith falls from Stage 1 into Stage 2
- Water percolates down through Stage 2
- Biochar has to travel up from Stage 3 into Stage 2
Options under consideration: move the furnace alongside rather than below; treat biochar as a periodic manual recharge rather than a continuous flow; or invert the stack and accept a conductive heat path instead of convection. Unresolved, and documented as unresolved.
Contamination control
Two things here are invisible and both contaminate. Perchlorate is one. Dust is the other: a system that moves regolith inside a habitat is itself a source of respirable dust. NASA's limit for Martian dust is 0.1 mg/m³ as a 24-hour time-weighted average, stricter than the 0.3 mg/m³ set for lunar dust in NASA-STD-3001.
Introducing terrestrial bacteria to Mars is a planetary protection question under COSPAR policy. Stage 1 is a fully contained reactor.