Oxygen content in water/ water breathing.

[magnemoe]

Something I have been wondering about and the co2 and water tread brings back.

Found that water normally contains 8-10 mg oxygen in water, more in cold. and that oxygen at one bar is 750 liter/kg at one bar.

This gives 7.5 milliliter or cm^3 oxygen for one liter water, or 37 cm^3 air, it does not sounds like much, how do fish manage, they don't have to breath a lot of water.

[GDJ]

Gills are far more efficient in getting O2 out of the water.

Eventho' there is quite a bit of O2 in water, it's nothing compared to what we have on land. Our lungs just can't get O2 out of water since they are designed for O2 scavenging in atmosphere, hence we drown.

Fish do drown in our atmosphere, but for a brief minute or two, they are exposed to more O2 than they ever had, but too much O2 is toxic, hence they "drown" in a way.

Eventho' a small fish has tiny lungs (gills), they probably have as much surface area to grab O2 as a larger land animal.

That's how I see it.

[Exoscientist]

Then there's this:

Oxygen absorbing material may allow us to breathe underwater.

By Colin Jeffrey - October 4, 2014

http://www.gizmag.com/crystalline-material-absorb-oxygen-denmark/34064/

Bob Clark

[GDJ]

That's pretty cool!

[windows_x_seven]

Then there's this:

Oxygen absorbing material may allow us to breathe underwater.

By Colin Jeffrey - October 4, 2014

http://www.gizmag.com/crystalline-material-absorb-oxygen-denmark/34064/

Bob Clark

AFAIK there is a problem with breathing underwater, which is getting CO2 out of the body.

Perhaps using perfluorocarbons (liquid breathing) would be more efficient.

[RainDreamer]

Another problem is that our lungs are not designed to breathe fluid. They can't expel fluid very efficiently, and fluid in lungs is a serious medical problem.

Fluid breathing is not something we can do for a long time, even if we do get enough O2 from the fluid we take in.

Edited August 6, 2015 by RainDreamer

[ZetaX]

Fish do drown in our atmosphere, but for a brief minute or two, they are exposed to more O2 than they ever had, but too much O2 is toxic, hence they "drown" in a way.

Most fish wouldn't "drown" on land. They should have no problem in spending a few minutes on land; if the water lacks enough O_2 then even come to the surface to breath air. They only die after their gills dry out, only then they die due to lack of oxygen.

[lajoswinkler]

Fish have a different physiology than mammals. They are cold blooded and thus don't require that much oxygen. Everything, including their relatively stupid brains compared to the most primitive mammal, gets enough oxygen by taking over oxygen dissolved in water.

If you want your body to be heated up all the time, if you want to run and to think a lot, you need more oxygen. Evolutionary standpoint.

Breathing in fluorinated hydrocarbons with dissolved oxygen inside is not a new thing, but not much has been done since the first experiments. It is not a benign process. Alveolar damage occurs and you get blood in the exhaled liquid.

[PB666]

Fish have a different physiology than mammals. They are cold blooded and thus don't require that much oxygen. Everything, including their relatively stupid brains compared to the most primitive mammal, gets enough oxygen by taking over oxygen dissolved in water.

If you want your body to be heated up all the time, if you want to run and to think a lot, you need more oxygen. Evolutionary standpoint.

Breathing in fluorinated hydrocarbons with dissolved oxygen inside is not a new thing, but not much has been done since the first experiments. It is not a benign process. Alveolar damage occurs and you get blood in the exhaled liquid.

Not stupid brain but small, Some fish are pretty clever, groupers for instance. The metabolism is slower, they do not need to waste energy to cool down (such as sweating) and for freshwater fish they simply dump ammonia into the water rather than process it to something less toxic. They also breath through their skin. If you take a look at the meat of most fish (except the deep ocean bill fish, tuna and like) they have white meat, this is what the call fast twitch muscle, it tends to work only for breif periods and conserves energy by not having alot of mitochondria slow burning fat and glucose.

[Exoscientist]

BTW, running some numbers I think it would be doable technically to do electrolysis to separate the oxygen out of water at a much lighter weight than a scuba tank, which run about 15 kilos for about an hour's worth of breathing time underwater.

To chemically separate the hydrogen and oxygen in water takes about 16 million joules of energy per kilo of water. This is at 100% efficiency. I don't know what the best efficiency actually is now but we'll see the amount that can done be using batteries is so high that likely it can be better than using scuba tanks for the same weight.

The ratio of oxygen to hydrogen in water by mass is 8 to 1. So using 16 megajoules of energy you get 8/9 of a kilo of oxygen. This means 16*(9/8) = 18 megajoules gives 1 kg of oxygen. As a rough estimate take the amount of oxygen someone needs in 24 hours as about 1 kilo.

Now for the weight of batteries. See this table for a list of energy densities per weight:

https://en.wikipedia.org/wiki/Energy_density#Energy_densities_of_common_energy_storage_materialsy

The best energy density among the commonly available batteries is the lithium battery (non-rechargeable) at 1.8 megajoules per kilo. Then to provide the 18 megajoules to get 1 kilo of oxygen you would need 18/1.8 = 10 kilos of the lithium batteries. I'll assume the weight of the system will be dominated by the weight of the batteries since electrolysis can be done simply by placing electrified wires in the water. So at 15 kilos of the batteries, the same weight as the scuba tank for 1 hour of breathing time, you would actually get enough oxygen for (15/10)*24 = 36 hours, a day and a half. Or said another way, to get enough oxygen for 1 hour would only take 10/24 = .42 kilos, less than a pound.

Practical problems of course are for one how efficient is the electrolysis procedure? Also I believe the lithium batteries catch fire when wet. You would need to insure the battery casings are super-waterproof.

Then there is the weight of the electrolysis components, and the weight of the tank to hold the oxygen as it is being produced. You would also need to dispense with the hydrogen in a way to insure it does not combine with the oxygen to catch fire. It might be sufficient for this to mix it with surrounding water.

[Vanamonde]

Land animals also need to expend energy holding their bodies up with muscles, whereas fish are effectively weightless. I suspect there's a saving of effort and oxygen consumption there.

[arkie87]

Dont forget about the dependence of solubility on pressure. Just 10 meters down, is twice the pressure. http://www.engineeringtoolbox.com/air-solubility-water-d_639.html

EDIT: i guess that effect doesnt matter, since there is no way concentration can diffuse against the gradient

Edited August 7, 2015 by arkie87

[Stargate525]

Then there is the weight of the electrolysis components, and the weight of the tank to hold the oxygen as it is being produced. You would also need to dispense with the hydrogen in a way to insure it does not combine with the oxygen to catch fire. It might be sufficient for this to mix it with surrounding water.

There's a way to separate them, I think it has something to do with the poles of the electrode.

But you're missing a pretty vital component; scuba tanks aren't oxygen tanks, they're AIR tanks. Pure oxygen is extremely toxic. So you'd either be attaching this to a rebreather mechanism (in which case your limit is the rebreather's ability to scrub CO2) or will have to truck down a tank of nitrogen to balance your oxygen generation.

[shynung]

Land animals also need to expend energy holding their bodies up with muscles, whereas fish are effectively weightless.

Not necessarily. Some reptiles do not actually stand on their legs, but rather lay on their bellies. When at rest, they don't spend energy keeping themselves standing or balanced.

[magnemoe]

Then there's this:

Oxygen absorbing material may allow us to breathe underwater.

By Colin Jeffrey - October 4, 2014

http://www.gizmag.com/crystalline-material-absorb-oxygen-denmark/34064/

Bob Clark

Interesting, another use here might be submarines, who don't care so much about bulky equipment than an human, it might even be possible to run an fuel cell with the oxygen.

For diving it would not solve the rebreather problem, you breath pure oxygen and co2 is removed while more oxygen is added. You would need to have nitrogen or an other gas in the loop

For space suits I think they use rebreathers, they however don't have the pressure problem, running pure oxygen at 1/5 bar is just an benefit.

[magnemoe]

Fish have a different physiology than mammals. They are cold blooded and thus don't require that much oxygen. Everything, including their relatively stupid brains compared to the most primitive mammal, gets enough oxygen by taking over oxygen dissolved in water.

If you want your body to be heated up all the time, if you want to run and to think a lot, you need more oxygen. Evolutionary standpoint.

Breathing in fluorinated hydrocarbons with dissolved oxygen inside is not a new thing, but not much has been done since the first experiments. It is not a benign process. Alveolar damage occurs and you get blood in the exhaled liquid.

Yes, the cold blooded part should save a lot of energy especially in water. Combine this with that gills are probably more efficient in that they absorb most oxygen while lungs only absorb an faction.

Making something amphibious/ water breathing while warm blooded would get heat exchange problems who would be far worse than extracting oxygen from the water.

Found answer to the original question, we uses around 820 g oxygen every day. That is 580 milligram minute, with 10 milligram oxygen in a liter water you would need 60 liter a minute or 1 liter every second.

That is quite a lot then you think that you have to push the water trough an filter.

[0111narwhalz]

Also note that gills have MASSIVELY more surface area than lungs, composed as they are of layered planes. Lungs, however, are composed of many spheres, which have about the worst surface-to-volume ratio. This means that while gills contact nearly all of the fluid, lungs still have a bunch of untouched fluid in the centers of the sacs. The reason that gills don't work in air is that the planes stick together due to surface tension. Little spheres don't have this problem, because the walls stand off each other far enough. Dry gills, however, don't work for reasons I couldn't state with certainty.

By the way, pure oxygen is not toxic at diver-safe pressures (though it will make you high), while nitrogen narcosis means that nitrogen causes more trouble than it's worth.

Edited August 7, 2015 by 0111narwhalz

[RainDreamer]

About electrolysis under water to generate O2... it is a safe thing to haul electronic compartments using and storing high amount of electricity on the back of a wet suit? On a mini submarine, maybe that is a viable solution, but I don't exactly want to wear that on my back while diving.

[Exoscientist]

Interesting, another use here might be submarines, who don't care so much about bulky equipment than an human, it might even be possible to run an fuel cell with the oxygen.

For diving it would not solve the rebreather problem, you breath pure oxygen and co2 is removed while more oxygen is added. You would need to have nitrogen or an other gas in the loop

For space suits I think they use rebreathers, they however don't have the pressure problem, running pure oxygen at 1/5 bar is just an benefit.

Yes. A major problem with this is normally scuba divers don't use pure oxygen. Usually it is compressed air with a normal mix of oxygen and nitrogen. In fact pure oxygen at too much of a depth can be toxic to divers:

What Scuba Tank Gas Mixture do Divers use?

Posted by Sandro Lonardi | October 05, 2013 |

http://www.elitedivingagency.com/articles/scuba-tank-gas-mixture-divers-use/

However, as you stated astronaut's spacesuits do use pure oxygen So instead of using heavy tanks to hold the compressed oxygen it might work to carry water which would be electrolysized to produce oxygen.

Bob Clark