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) and Dechloromonas aromatica (RCB). Neither is exotic or engineered — both occur in ordinary river sediment and soil.
Do not oversell the oxygen
The O₂ in that equation is an intermediate the same organisms consume. Net export to life support is close to zero. The benefit of this stage is detoxification, not oxygen production.
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 reverse osmosis with reduced load, so the machine works less and its membranes last longer. This is the stage built and measured on the bench.
Stage 3 — Pyrolysis
Organic waste and cellulosic packaging are heated to roughly 450 °C without oxygen. The material does not burn, it chars: pathogens are destroyed, volatile gases driven off, and what remains is biochar — porous, with high cation exchange capacity.
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 furnace runs at 450 °C. The bacteria need 20–35 °C and the Martian surface averages −63 °C. Placing the furnace at the bottom lets that heat rise. |
| Electron donor | The bacteria need a carbon source to respire perchlorate at all. Volatile fatty acids from processing the same waste supply it. |
Remove Stage 3 and Stage 1 freezes and starves. 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 in this challenge 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. The design limit is 0.1 mg/m³ as a 24-hour time-weighted average, stricter than the 0.3 mg/m³ general figure in NASA-STD-3001.
Introducing terrestrial bacteria to Mars is a planetary protection question under COSPAR. Stage 1 is a fully contained reactor.