[Chemistry][Theory] Artificial Photosynthesis to replenish Oxygen

[NERVAfan]

In fact, that "biodome" (Biosphere-2) just have shown that you would need to be a sorcerer just to let 7 humans leave in balance with ecology.

No, it doesn't show that at all. Biosphere 2 was very badly designed. I (or anyone with half a clue about ecology and agriculture) could do much better, especially with their bad example

It was designed to mimic Earth ecosystems. But...

A) that doesn't work in the first place because on Earth you do not have desert 100 meters from rainforest (and indeed the desert stopped being desert);

this is hideously inefficient for human life support if you are mass-limited; you should design like a farm (with air as a "crop") not like a natural system;

C) this meant lots of extra work for the crew to try to do stuff like scrub algae off the coral reef.

Also, they didn't plan for the day/night and winter/summer carbon dioxide/oxygen variation (easily solved if you know it exists).

Also, their structure wasn't inert; the new concrete absorbed oxygen.

Imagine, that they have left one part of their paradise because of plant-louse,

Erm, how did these plant lice arrive? You only have the species you brought with you.

or fire, or decompression.

Fire and decompression are catastrophic in any spacecraft.

Or imagine their plantation gave a bad harvest just because potato had disliked their fec... fertilizer.

Why would that happen? Fertilization of crops with human waste is hardly some new untried technology.

So, to guarantee that they will not starve to death, first of all you must provide them with several times superfluous plantation than they indeed need.

You need some margin, yes.

To provide this paradize with fertilizer you will need (say, on Mars) store large ammonia cysterns  to produce nitrates, as by definition this plantation would need much more than all the crew can sh... produce even trying their best.

No. Mass is conserved. The nitrogen is consumed from the crops by humans, excreted and returns to the crops. There will be some loss as nitrogen gas, but you include nitrogen-fixers to solve that problem.

You will probably actually have extra fixed nitrogen, since the humans will bring food to eat before the first crop is ready to harvest, which will be excreted and added to the plants.

Edited December 16, 2014 by NERVAfan
fixed quote

[NERVAfan]

To expand on that... farms on Earth need lots of nitrogen fertilizer input because the farm is not a closed system. The crop is removed from the farm and consumed far away - nitrogen is lost from the local system.

But the Earth is a closed system, and no nitrogen is imported. A space greenhouse would be more analogous to the whole Earth - the nitrogen cycle is completed locally, within the system.

[kerbiloid]

Erm, how did these plant lice arrive? You only have the species you brought with you...

Fire and decompression are catastrophic in any spacecraft.

Imagine you have a well designed, self-sufficient closed-loop ecosystem village-under-a-dome.

It consumes exactly the same amount of substances which your crew can produce, and produces exactly the same amount of food and air your crew would consume.

A short circuit destroys your aeroponics pump, a half of your plantation die.

As your system is precisely designed to replace 100 kg of waste with 100 kg of goodies, and now it can produce only 50 kg, will you reduce you crew twice?

Or imagine their plantation gave a bad harvest just because potato had disliked their fec... fertilizer.

Why would that happen? Fertilization of crops with human waste is hardly some new untried technology.

Er... It not that "would", but it "does". Any plantation harvest varies from year to year.

Fishes in aquarium from time to time unpredictabely die, and algae either grow or rot.

You can predict whether your harvest will be 30 or 50 t, but not 40 or 45.

You can't predict if some of your potatoes grow ill or just unhappy  it's usual uncertainty of any agricultural affairs.

So, you would anywhere take this into account in your estimations. And use a bottom value, designing a surplus system which will be anyway not balanced with the crew needs.

As a result you will contain a self-sufficient system without humans, where humans can take what they want frokm time to time.

It looks beautiful but several times greater than you crew really needs, so it's a very expensive joy.

For example: any hinge must contain a slop betweens details. A hinge without a slop will wedge on any tiny condition change.

Those notorious "close loop ecosystems" are such hinges without slops. Any change  and you get an avalanche of disbalances.

Mass is conserved. The nitrogen is consumed from the crops by humans, excreted and returns to the crops.

There will be some loss as nitrogen gas, but you include nitrogen-fixers to solve that problem.

You will probably actually have extra fixed nitrogen, since the humans will bring food to eat before the first crop is ready to harvest, which will be excreted and added to the plants.

First of all, mass conservation law is a theoretical abstraction.

It is great in chemical equations, but why you need to wash your flasks after chemical studies and wash your plates after eating?

Because any system has a conversion efficiency parameter, and it never be 100%.

Some part of substances will anyway be lost in a random manner: as an effuse, as leakage, as an obstinate dirt, just as some chemical artefacts which is easier to replace than to dissolve.

There no 100% filters to separate gases atom by atom.

Also when you talk about any biological products, you can't predict illnesse, diarrhea and so on. So, an "output product" would widely vary.

As a result, you would dispose yourself to: any ecosystem wider than one fish tank will have have a loss for (dozens) percents per cycle.

To replace the loss you need (see above) an opened system being daily replenished from outside.

But the Earth is a closed system, and no nitrogen is imported.

A space greenhouse would be more analogous to the whole Earth - the nitrogen cycle is completed locally, within the system.

Earth is not a closed ecosystem.

First, it gets energy from two exhaustible sources: depths and Sun, for 4.5 billin years.

Estimated, depths energy (produced by gravitational differentiation of mass) will finish 1.5 bln years later. I.e. 75% of time allowed is exhausted.

Sun energy  vice versa  grows ~10% per billion years. Estimated 1 bln year the Earth surface will be like Venus one. I.e. 80% of time allowed is exhausted.

So, Earth energy is like weight driven clock:

https://www.google.ru/search?q=weight+driven+clock&newwindow=1&tbm=isch&tbo=u&source=univ&sa=X&ei=IcuPVPTwL8PMygOv8oK4CQ&ved=0CB0QsAQ&biw=1760&bih=897

Second, Earth gets carbon dioxide and water from volcanic gases. They come from depths, while the rocks drain-out.

Then a free carbon is burried as a bog mud, millions year after becoming a coal. The free oxygen stays in air allowing us to breathe.

Thrid, live species do not stay stable. They evolve and from time to time die. This is not very appropriate for a crew or precisely designed ecosystems.

Btw about nitrogen in "closed Earth ecosystem":

Atmospheric nitrogen 4e18 kg

Plants 2.4e15 kg.

Animals and bacteria 2e13 kg.

I.e. 100 t of atmospheric nitrogen per 1 kg of animal biomass. Probably, not the best template for artificial system.

Edited December 16, 2014 by kerbiloid

[ZetaX]

Imagine you have a well designed, self-sufficient closed-loop ecosystem village-under-a-dome.

It consumes exactly the same amount of substances which your crew can produce, and produces exactly the same amount of food and air your crew would consume.

A short circuit destroys your aeroponics pump, a half of your plantation die.

As your system is precisely designed to replace 100 kg of waste with 100 kg of goodies, and now it can produce only 50 kg, will you reduce you crew twice?

I think you are making up unrealistic scenarios ("strawmen") on purpose to search flaws in those instead of adressing the general manner. First Biosphere 2 and now this.

And to answer it: who would be so stupid and not have spare parts¿ If we have this supposedly easy metallurgy we would not even need to bring them with us. And obviously we would aim for some overproduction allt he time to have some food in storage in case of problems.

Er... It not that "would", but it "does". Any plantation harvest varies from year to year.

Yeah, because a geodome would _obviously_ face the same reasons like weather and unexpected import of parasites, right¿ /sarcasm

Fishes in aquarium from time to time unpredictabely die

Yeah, single ones. Take 10000 fish and this is just a statistic.

You can predict whether your harvest will be 30 or 50 t, but not 40 or 45.

I would claim we can do the latter. But regardless, we would then aim for the 30t to be enough, everything else is bonus and allows an easier second year.

And use a bottom value, designing a surplus system which will be anyway not balanced with the crew needs.

What "needs" are you talking about¿ Obviousy, living on mars/moon is no luxury in the beginning. It will be corn products every second day, cheap bread every other day, and some potato mash in between or something like that. All minor vitamin problems could easily be dealt with using stuff from earth, the mass would be insignificant.

For example: any hinge must contain a slop betweens details. A hinge without a slop will wedge on any tiny condition change.

Those notorious "close loop ecosystems" are such hinges without slops. Any change  and you get an avalanche of disbalances.

There obviously is at least one stable ecosystem called "earth" (for pragmatic nitpickers: add the moon and sun into the system). Thus your argument is invalid as it did nowhere adress why or how size should matter.

It is great in chemical equations, but why you need to wash your flasks after chemical studies and wash your plates after eating?

Because there are reasons we want them to be clean for the next use. This is not caused by the remainder being worthless waste that could not be recycled.

Because any system has a conversion efficiency parameter, and it never be 100%.

Some part of substances will anyway be lost in a random manner: as an effuse, as leakage, as an obstinate dirt, just as some chemical artefacts which is easier to replace than to dissolve.

There no 100% filters to separate gases atom by atom.

They won't be lost in a _closed_ biosphere. That's the definition of that word. We can easily build that. What we currently lack is to get them into a biologically stable state. And we don't need such filters.

any ecosystem wider than one fish tank will have have a loss for (dozens) percents per cycle.

To replace the loss you need (see above) an opened system being daily replenished from outside.

Counterexample "earth" again. Sorry, but it's really annoying if your arguments are contradicted with such ease. Try making ones that actually consider the given paramters (mass, size, limited species, whatever), but your current ones are just "I don't think closed ecosystems are possible", which is obviously wrong. Yes, you adress that later and I will now get to why that's ridiculous:

Earth is not a closed ecosystem.

First, it gets energy from two exhaustible sources: depths and Sun, for 4.5 billin years.

Estimated, depths energy (produced by gravitational differentiation of mass) will finish 1.5 bln years later. I.e. 75% of time allowed is exhausted.

Sun energy  vice versa  grows ~10% per billion years. Estimated 1 bln year the Earth surface will be like Venus one. I.e. 80% of time allowed is exhausted.

That's idiotic as a counterargument to biospheres. We want one that works for a couple of years. Earth obviously is and was stable for that time and even much longer.

Are you now starting to use entropy as an argument against doing anything because it will be irrelevant 10^100 years from now anyway¿

And please go to everyone talking about "regenerative energy" and tell them they are so wrong for the sun being finite; please put up videos^^

I would also doubt that 10% energy increase would turn earth into venus, but that's just the smaller and completely irrelevant flaw in there.

Second, Earth gets carbon dioxide and water from volcanic gases. They come from depths, while the rocks drain-out.

Then a free carbon is burried as a bog mud, millions year after becoming a coal. The free oxygen stays in air allowing us to breathe.

The only reason that CO2 is even relevant is because plants are allowed to store carbon as coal for almost forever. Not a relevant problem in anything like a biodome. This is not a short-term effect nd we could even prevent it from happening should we ever plan a million-year-dome.

Thrid, live species do not stay stable. They evolve and from time to time die. This is not very appropriate for a crew or precisely designed ecosystems.

It is more generally not appropriate for anything short-term having enough of each species.

Edited December 16, 2014 by ZetaX

[EzinX]

Here's the answer to the original post :

Sabatier Reaction :

CO2 + 4 H2 → CH4 + 2 H2O + energy

Pyrolysis :

CH4 + heat → C + 2 H2

Electrolysis :

2 H20 -> 2 H2 + 02

You need a catalyst that is not consumed for all 3 reactions, made of platinum or something. Hydrogen in this case is also acting as a catalyst. The pyrolysis of CH4 to carbon residue and hydrogen gas leaves this dirty soot over your catalyst which has to be removed somehow (maybe you can blast it loose with ultrasonic sound waves or something)

[NERVAfan]

Imagine you have a well designed, self-sufficient closed-loop ecosystem village-under-a-dome.

It consumes exactly the same amount of substances which your crew can produce, and produces exactly the same amount of food and air your crew would consume.

A short circuit destroys your aeroponics pump, a half of your plantation die.

As your system is precisely designed to replace 100 kg of waste with 100 kg of goodies, and now it can produce only 50 kg, will you reduce you crew twice?

It's not that precise. Plants are not photosynthesizing at 100% of capacity constantly, etc. There is a significant degree of compensation built in, because of the fact that living things respond to different conditions differently.

And you can help that along by altering light levels and stuff.

(Also, don't use one pump for 1/2 your whole system! And things don't usually die instantly in a situation like that; there should be time to fix things.)

Also, I wouldn't use aeroponics, but...

Er... It not that "would", but it "does". Any plantation harvest varies from year to year.

Fishes in aquarium from time to time unpredictabely die, and algae either grow or rot.

You can predict whether your harvest will be 30 or 50 t, but not 40 or 45.

You can't predict if some of your potatoes grow ill or just unhappy  it's usual uncertainty of any agricultural affairs.

There will be some uncertainty, but in a well designed system for this purpose (NOT Biosphere 2*) there will be much less than you would think from Earth examples, since the system is closed and tightly controlled. No weather, no floods, no droughts, no diseases or pests introduced.

*To be fair, Biosphere 2 was trying to do a lot of things at once. It was not specifically an attempt to create a space life-support-system. However, I think it has given a very skewed picture of how difficult the problem really is.

So, you would anywhere take this into account in your estimations. And use a bottom value, designing a surplus system which will be anyway not balanced with the crew needs.

As a result you will contain a self-sufficient system without humans, where humans can take what they want frokm time to time.

It looks beautiful but several times greater than you crew really needs, so it's a very expensive joy.

There would indeed be some margin, but not so much that it would be problematic. Also, the system is self balancing to some degree.

Those notorious "close loop ecosystems" are such hinges without slops. Any change  and you get an avalanche of disbalances.

It won't be forever. But neither is the Earth, technically.

You can get 2-3 years reliably, 10+ years sometimes, of successful closure in an ecosystem the size of a basketball or smaller (they're sold commercially as Ecospheres). I don't see why several thousand years in something the size of a base/colony should be so impossible.

Either this will be on a mission/spaceship, in which case you probably only need it to work for single-digit number of years. Or it will be on a base of some sort, in which case it doesn't have to be 100% perfectly closed, as you can introduce extra water/carbon/etc. from the Moon ice or Mars ice/atmosphere or whatever body you have the base on.

Because any system has a conversion efficiency parameter, and it never be 100%.

Some part of substances will anyway be lost in a random manner: as an effuse, as leakage, as an obstinate dirt, just as some chemical artefacts which is easier to replace than to dissolve.

There no 100% filters to separate gases atom by atom.

Then why didn't the earth run out of nutrients billions of years ago?

Because the losses are miniscule when the system is considered as a whole - the biosphere has a way of re-harvesting almost everything. You don't immediately get 100% of the gas back, but over time the biologically fixed nitrogen that is emitted as nitrogen gas is fixed back into biologically useful forms, etc.

Things are only lost from the system when they are removed from the habitable parts of the Earth entirely (water split by lightning or UV and the hydrogen escapes to space, carbon trapped in deep layers as fossil fuels), or, currently, turned into certain technological chemicals that life can't use. Pretty much all wastes are recycled.

Also when you talk about any biological products, you can't predict illnesse, diarrhea and so on. So, an "output product" would widely vary.

As a result, you would dispose yourself to: any ecosystem wider than one fish tank will have have a loss for (dozens) percents per cycle.

No way. Even Biosphere 2 did enormously better than that.

Earth is not a closed ecosystem.

First, it gets energy from two exhaustible sources: depths and Sun, for 4.5 billin years.

OK, true, but not relevant to what we are talking about. Technically the right term for the systems we're discussing is "materially closed" as the matter cycles but you need new energy from outside.

Second, Earth gets carbon dioxide and water from volcanic gases. They come from depths, while the rocks drain-out. Then a free carbon is burried as a bog mud, millions year after becoming a coal. The free oxygen stays in air allowing us to breathe.

Not really. Yes, volcanoes emit CO2, but CO2 is geologically lost as carbonate rocks too, and IIRC this is actually a net loss of carbon.

Anyway, this is irrelevant. The abiotic / geological carbon cycle (and the creation of fossil fuels) matter on a timescale of millions of years or more. It's not relevant to a life support system on a human scale.

On human timescales (without fossil fuel burning involved, anyway), the carbon cycle really is:

carbohydrates + O2 -> CO2 + H2O (respiration)

balanced by

CO2 + H2O -> carbohydrates + O2 (photosynthesis)

Thrid, live species do not stay stable. They evolve and from time to time die. This is not very appropriate for a crew or precisely designed ecosystems.

I'm not really talking about designing for geological time scales. Getting it to last 6,000-8,000 years or so (the whole history of human civilization) ought to be just fine

[kerbiloid]

I think you are making up unrealistic scenarios ("strawmen") on purpose to search flaws in those instead of adressing the general manner.

I believe that I describe much more realistic scenarios than "green happy Mars", and definitely not trolling  if you mean that.

If my manner of speech seems too agressive, I'm sorry, that's not my aspiration.

I just had honestly tried to calculate resources consume/produce rates for a closed-loop system (earlier  just of curiosity, and later  to build a self-sufficient KSP base) and realized that to keep it stable, not a crystal doll-house, you would created a  yeah, over-producing  system where the crew would be just excluded and treated as a small quantity of outer parasites not affecting it too much.

who would be so stupid and not have spare parts¿ If we have this supposedly easy metallurgy we would not even need to bring them with us.

Spare parts are fine to repair some small trouble.

But the main closed-loop ecosystem disadvantage is that it can not be easily simplified, splitted or scaled  as electrical/chemical refinery. If it goes  it goes massively, no "75%" or "90%".

You are just accustomed to Earth conditions where humanity needs are many times less than total biosphere production.

Yeah, because a geodome would _obviously_ face the same reasons like weather and unexpected import of parasites, right¿ /sarcasm ... Take 10000 fish and this is just a statistic.

You didn't ever have a yard with rabbits or aquarium with decorative fishes, did you?

They also do not face weather or meteorite storm, but they like to unpredictably ill or die, and often  several per week.

Also, if rabbits (being fed, warmed and cured by owner) begin to die, then can die dozens a week. And later they reproduce dozens a month. If you have another food  no problems, but we speak about a closed system. So, to compensate rabbits mass death, you would have, say, another yard of chickens. So, you would already increase you ecosystem twice than needed  until the ecosystem becomes you aim instead of give a food to the crew.

We want one that works for a couple of years.

If you want just to works a couple years, it's definitley much easier not to build an ecosystem, but to drop them enough food supplies. Also, you can any time resupply using slow-moving ion-powered unmanned cargo ships: who cares if 10 tons of frozen meat will fly for several years, it isn't afraid of radiation.

[kerbiloid]

...

As I have written a bit above, the common problem of all this greenhouse-based life support system is that its followers scale their Earth patterns to an empty room circumstances.

To avoid misunderstanding: I don't mean that such greenhouses are impossible or useless at all.

The closed ecosystem solution is of course possible  but it must be overpowered a lot, as any ecosystem is much less predictable and scalable than a simple and stupid technical device.

You can split a chemical/electrical refinery to thousand of parts and if something varies, 800 of 1000 will produce 80% of needed efficiency.

But minimal self-sufficient portion of ecosystem will not allow to have 1000 to loose 200. It would be enough large to have, say, 2-3 independent systems at once, and loose 1/3..1/2 if something happens.

So, bio-based life support is a privilege of metropolis-sized colony, not of a single ship or 1000-human groundbase. Quod liced Iovi  non liced bovi.

And brave starshipmen and frontier colonists would eat their Earth-manufactured snax and be happy of that.

[NERVAfan]

Hmmm. I still disagree that it has to be nearly that big. (Biosphere 2 was very inefficient - I'm pretty sure you could make something significantly smaller work - and it's much smaller than a 1000-person base would be.)

Sadly, I don't have $1-$2 million or so to actually prove this.

(I think you could theoretically fit it into the mass/volume of a smallish RV per person, or less, for that matter, with careful choice of species - but there wouldn't be much margin, and it would be a pretty monotonous diet.)

EDIT: I'd say the ISS/Mir/Skylab is right about "too small to make it practical", but something 5-10 times bigger would probably be better served with an at least partially biological system.