A filter made from the soil it has to clean

Martian regolith contains perchlorate before anyone lands on it. It is not contamination the mission caused; it is how the planet is. While the soil is like that, nothing can grow in it and nothing can safely be built on it.

Meanwhile six crew produce greywater, food residue and packaging every day, and all of it ends up in that same soil. And water is far too valuable to use once, so it has to be recycled — the habitat already has a reverse osmosis unit, but used water reaches it heavily loaded.

Bacteria in a sealed chamber respire the perchlorate out of the regolith and leave inert chloride. An oxygen-free furnace chars the crew's waste into biochar. The cleaned regolith and that biochar are layered into a column, and greywater percolates down through it, reaching the reverse osmosis unit far cleaner than it left.

What ties it together: the furnace runs at 450 °C, and the bacteria need to sit at 20–35 °C on a planet averaging −63 °C. The furnace heats them. It also feeds them — perchlorate-reducing bacteria need a carbon source to respire at all, and that comes from processing the same waste. Remove the furnace and the bioreactor freezes and starves.

Read the full system →

Stage 2, the filtration column, is built on a bench and measured. Stages 1 and 3 are supported by published work. Perchlorates are strong oxidising salts and are not handled in this project.

The bench column substitutes Earth materials for the Martian ones. Volcanic scoria, a basaltic rock, stands in for regolith. The biochar is not a substitute at all — it is real biochar, made from fibrous agricultural residue such as sugarcane bagasse, coconut husk or rice husk.

The same column, built from local volcanic rock and agricultural residue char, works as decentralised passive pre-treatment for household water storage. In many places piped water does not arrive clean and households store it before use. That is not an analogy drawn after the fact — it is the same hardware.