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I was thinking about how in The Martian the astronaut used the crew members poop to fertilize the soil and grow potatoes and decided to learn more about that. I read, though, that unprocessed human waste has pathogens that make it risky to use. The only way I saw to make it safe is to let it sit for a year and then compost it but to only use it on non edible plants. Instead of doing all that, couldn’t you just soak the poop in bleach and then let the bleach evaporate to kill all the pathogens? Then you know it would be safe to use for edible plants.

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  • The bleach would not kill the pathogens inside the poop. Also, the spores of spore-forming bacteria (clostridium etc) will not be killed in any case by bleach. Pressure cooking for at the correct time, pressure and temperature will work fine. – Polypipe Wrangler Jan 26 at 2:14
  • I tend to agree that it wouldn't kill everything (just some things). A better approach than bleach might be to incinerate the poop into fine ash. Make sure there's no medication in it or the fumes could be harmful, and the medication might not be good for plants. Note that poop ash isn't the same nutrient-wise as wood ash, and would probably be safe to use as far as pH goes. A wood stove fire can get up to 2000° F., which I believe would kill pretty much anything. – Brōtsyorfuzthrāx Jan 27 at 2:35
  • Wouldn’t incinerating it make it lose some of the nutrients as gas? – user11937382 Jan 27 at 2:36
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The soil that potatoes grow in is a machine whose function is to process nutrients and store water in a form that the root hairs of the plant can absorb. Apart from the mineral element there is a community of other organisms that facilitate this process. Chlorine is an effective killer of many organisms but so is radiation. My understanding of radiation is limited but it seems to me that just putting the human waste out in the Martian fresh air would expose it to heavy radiation effectively killing over time many if not all the organisms in the waste.

The problem with chlorine and radiation is they are both broad spectrum killers. As far as I am aware Martian soil at the surface is inert, so mixing dead soil with dead waste provides no soil community to process complex materials in the waste into primary stuff that the root hairs can handle. Normal composting has the effect of suppressing those organisms of no use in the growing process and encouraging those that help plants to grow.

The availability of potatoes was a convenient happenstance. Not only is the potato more able to process raw nutrients and sit around waiting for them to become available, but also can be thinly peeled where there is a suspicion of pathogens on the surface of the tubers, the peel being recycled back into the soil.

"F U Mars."

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