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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.

called2voyage
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  • 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. – Deer Hunter Jul 30 '13 at 17:17
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    @DeerHunter That may be the case, but space colonies are in the scope of the question. – called2voyage Jul 30 '13 at 17:19
  • Oh, I see. I suppose you have already read the wiki article: https://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... – Deer Hunter Jul 30 '13 at 17:30
  • And this one: https://en.wikipedia.org/wiki/NEWater – Deer Hunter Jul 30 '13 at 17:32
  • @TildalWave - recycling liquids is fine. We already do that. Recycling solid waste is a problem (it saps precious energy and oxygen from the habitats for no particular gain). On Mars, planetary contamination becomes an issue. – Deer Hunter Jul 30 '13 at 17:35
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    "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 – called2voyage Jul 30 '13 at 17:36
  • @DeerHunter The above quote claims that the rigorous process you describe is unnecessary for use as compost. – called2voyage Jul 30 '13 at 17:38
  • @TildalWave "But there are huge problems with that outside of Sci-Fi and some yet unimplemented ideas." That's not outside of the scope of the question either. – called2voyage Jul 30 '13 at 17:40
  • Called 2 voyage: and to achieve this final stage we have to build large plants. A permanent colony may choose to do that. – Deer Hunter Jul 30 '13 at 17:40
  • @TildalWave I'm glad it's of interest for more than just me. :) – called2voyage Jul 30 '13 at 17:45
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    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. – Jeremy Kemball Aug 22 '13 at 15:11
  • Haven't had time to dig into the source yet, but here's a new poop study: https://www.usatoday.com/story/news/nation-now/2018/02/01/we-can-use-poop-make-space-food-study-says-sing-poop-make-food-could-help-deep-space-exploration-stu/1086813001/ – called2voyage Feb 02 '18 at 21:11
  • @JeremyKemball true, BUT my gardening experience of a few years says that plants grow much better/longer/healthier when there are (beneficial) micro-organisms in the compost that help digest the organic material into molecules usable by plants, and provide e.g. nitrogen, in exchange for some glucose from the plant. Soil bacteria, fungi, and other micro-organisms live in a beneficial symbiosis with plants. – frIT Sep 08 '21 at 08:10

2 Answers2

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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:

called2voyage
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  • called2voyage - what are the scales of the process? How large is the notional equipment/bioreactor? – Deer Hunter Aug 08 '13 at 19:46
  • @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. – called2voyage Aug 08 '13 at 19:58
  • 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. – Deer Hunter Aug 08 '13 at 20:12
  • @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. – called2voyage Aug 08 '13 at 20:27
  • And the Earth-oriented work on microbial fuel cells seems to continue to march on: http://pubs.rsc.org/en/content/articlelanding/2015/ra/c5ra06211j#!divAbstract and http://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. – called2voyage Jun 05 '15 at 17:06
  • NASA bioreactor research to continue on the ISS: https://www.nasa.gov/mission_pages/station/research/experiments/92.html – called2voyage Jun 21 '17 at 14:01
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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.

James Jenkins
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  • 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. – called2voyage Jul 30 '13 at 22:05
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    @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. – James Jenkins Jul 30 '13 at 22:11
  • 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. – Mike H May 11 '16 at 04:19
  • @MikeH Maybe you should try and develop your comment into an answer. If your understanding is correct, it would be a great answer. – James Jenkins May 11 '16 at 10:14
  • 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. – Mike H May 12 '16 at 08:59