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After reading and answering James Jenkins's interesting question on wiping in space, I was curious about the usage of solid waste on a manned space vessel. In his question he mentions recycling solids in a farm, and during my research to answer his question I discovered that one paper discussed the possible use of dried human waste as a radiation shield.

I'm not really concerned with what is done with waste presently, but if there are any current recycling methods for human waste (excluding urine) they may certainly be addressed. Here's what I'm wondering: what is the most optimal method of recycling human solid wastes for sustainibility on a manned space vessel?

I'll set the maximum limit on future development to be the rearrangement of molecules. Once we have technology on that scale, the reuse question is not as big of a concern (given that the energy requirements are low enough). Any future technology short of that, however, can be considered in the answer.

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  • $\begingroup$ Human waste recycling requires too large facilities and is not economical in anything but space colonies. Using "night soil" in agriculture is essentially fraught with microbiological perils. I'd wait for anybody else's answer though since I'm not into microbiology. $\endgroup$
    – Deer Hunter
    Commented Jul 30, 2013 at 17:17
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    $\begingroup$ @DeerHunter That may be the case, but space colonies are in the scope of the question. $\endgroup$
    – called2voyage ♦
    Commented Jul 30, 2013 at 17:19
  • $\begingroup$ Oh, I see. I suppose you have already read the wiki article: en.wikipedia.org/wiki/Sewage_treatment I would guess that unless there is enough excess oxygen, the best way is to dump the waste outside. So much for sustainability... $\endgroup$
    – Deer Hunter
    Commented Jul 30, 2013 at 17:30
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    $\begingroup$ "Finished compost should never be “sterile,” but it should be sanitary. That means the compost should be teeming with beneficial microorganisms that do not pose a threat to human health. Any human disease organisms that may have been in the original organic material should have been eliminated, weakened, or greatly diminished by the time the compost has become mature. Finished compost can be tested for both the existence of pathogens as well as for agricultural quality (testing labs are listed in the Humanure Handbook)." - from the Humanure Handbook $\endgroup$
    – called2voyage ♦
    Commented Jul 30, 2013 at 17:36
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    $\begingroup$ The problem of radiation shielding and solid waste sterilization could solve one another, if we were clever. The poop shield would soak up the rads, and then we could grow food on the completely sterile space poop. $\endgroup$
    – Jeremy Kemball
    Commented Aug 22, 2013 at 15:11

2 Answers 2

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While answering according to actual optimal sustainability may not be strictly possible at the present, there is a method being currently researched by NASA that may provide one of the best solutions to managing human waste on a manned space vessel.

(As of 2004) Dr. Bruce E. Rittman of Northwestern University lead the NASA-funded team to experiment with the use of human waste as fuel for electricity in a process involving the use of Geobacter microbes for the generation of the electric energy. According to the NASA article, the best solution may be a combination of recycling the water from the waste, using it as fertilizer, and using it for electricity using this method that is currently being studied.

NASA has not released any updates on the progress of this research since 2007, though it has been alluded to in Earth-oriented work on microbial fuel cells as recent as 2016.

Source:

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  • $\begingroup$ called2voyage - what are the scales of the process? How large is the notional equipment/bioreactor? $\endgroup$
    – Deer Hunter
    Commented Aug 8, 2013 at 19:46
  • $\begingroup$ @DeerHunter Unfortunately, the article doesn't give much in the way of specs. There might be more info now as the article is from 2004, but I haven't been able to find any. $\endgroup$
    – called2voyage ♦
    Commented Aug 8, 2013 at 19:58
  • $\begingroup$ called2voyage - a quick search yielded no hits, have you tried Google Scholar already? I am afraid Dr.Rittman might have left us (the only article I found dated back to 1982) and thus the research came to naught. $\endgroup$
    – Deer Hunter
    Commented Aug 8, 2013 at 20:12
  • $\begingroup$ @DeerHunter This article says that NIAC was still looking at the human-waste-based microbial fuel cell technology in 2007, but unfortunately there are still no references to any other sources. $\endgroup$
    – called2voyage ♦
    Commented Aug 8, 2013 at 20:27
  • $\begingroup$ And the Earth-oriented work on microbial fuel cells seems to continue to march on: pubs.rsc.org/en/content/articlelanding/2015/ra/… and onlinelibrary.wiley.com/doi/10.1111/1758-2229.12230/full. Perhaps NASA is waiting for the technology to mature before investing more research in its potential use in space. $\endgroup$
    – called2voyage ♦
    Commented Jun 5, 2015 at 17:06
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Assuming we as race we colonize beyond our planet, with sustainable methods in our biological needs. Large quantities of organic material will be required, regardless if you are farming hydroponically or in soil, organic components are required to grow plants. Soil is a combination of sand (minerals) and organics. The only known source of organics in the universe are byproducts of earth life. As there is a significant cost in raising these organics to orbit, it makes financial sense to husband those organics we do get to orbit.

Composting is a time honored, simple, first step in the recycling of organic products like Night soils. It does not require significant investments in technology, infrastructure or human resources.

Current space habits are uniquely suited to support composting of night soils, as separation of solids and liquids is mutually desired. There many articles available on the subject, as this one points out, layering the dry night soils with materials that are high in cellulose or carbon is good first step. Generally composting principals of turning the compost (speeds breakdown), and encouraging a warm moderately dry (but moist) environment are all that is required.

The composted organic materials are then mixed with water (Hydroponics) or sand (soil), and used to grow plants. As with any farming operation, plants that are grown and eaten raw should be properly washed before consumption. Processing methods appropriate for destroys pathogens are used in other applications.

It can be expected that early space farm produce would be fresh vegetables for human/animal consumption and fiber rich plants that can be made into paper (toilet paper!), cloth, and for feeding Ruminants.

Of course everything goes back into the composting cycle. Note that while composting animal protein (meat) is possible it requires a level of skill beyond this simple method.

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  • $\begingroup$ What applications is this method useful for? You mention colonization, but for example, would it be useful in a ship traveling to Mars to colonize? More detail is required to make this a great answer. $\endgroup$
    – called2voyage ♦
    Commented Jul 30, 2013 at 22:05
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    $\begingroup$ @called2voyage was not shooting for a great answer, just an ok one. Hopefully someone will leverage on this to give a great answer. As for the ship going to Mars, simply saving the organics for the colony would be sufficient (implied by husbandry line), you already paid to ship them to Mars, it would be inexcusable to throw them away. If you are making a round trip, drop at Mars and Earth orbit. $\endgroup$
    – James Jenkins
    Commented Jul 30, 2013 at 22:11
  • $\begingroup$ I am curious about the claim that hydroponics require organic inputs, It is my understanding that the inputs required are only inorganic ions provided by inorganic salts. $\endgroup$
    – Mike H
    Commented May 11, 2016 at 4:19
  • $\begingroup$ @MikeH Maybe you should try and develop your comment into an answer. If your understanding is correct, it would be a great answer. $\endgroup$
    – James Jenkins
    Commented May 11, 2016 at 10:14
  • $\begingroup$ According to the Wikipedia - Hydroponics - article, inorganic salts (ions) are the nutrient solutions only ingredients. (Organic solution hydroponics can be done but seems to have disadvantages.) So hydroponic nutrient solutions require no carbon, which all comes into a plant via leaves. To close the system, the carbon in poo would have to be made available to the plants as CO2. $\endgroup$
    – Mike H
    Commented May 12, 2016 at 8:59

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