Algae producing oxygen in diving cylinder?

  • #1

Main Question or Discussion Point

Since algae can produce oxygen in closed containers, which you can inhale as a byproduct, when provided CO2 from your lungs; you could in theory take diving cylinders filled with algae with you, when diving, correct? I suppose this hasn't been done before, why not?
 
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Answers and Replies

  • #2
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Did you check how much O2 they produce? I did not find that number, but something like ~100 biomass tons per year and hectare here. Assuming this is purely carbon from CO2, it releases about ~200 tons O2. Downscaled, this is 0.5milligram/(m^2*s) in full sunlight. NASA calculates ~10mg/s for a human, this would require 20m^2 of algae (more, if you dive so deep that a part of the sunlight is blocked). Not really practical compared to conventional gas cylinders.
Air exhaled from your lungs has a high CO2 concentration, so it might improve growth a bit. But still... does not look practical.
 
  • #3
Did you check how much O2 they produce? I did not find that number, but something like ~100 biomass tons per year and hectare here. Assuming this is purely carbon from CO2, it releases about ~200 tons O2. Downscaled, this is 0.5milligram/(m^2*s) in full sunlight. NASA calculates ~10mg/s for a human, this would require 20m^2 of algae (more, if you dive so deep that a part of the sunlight is blocked). Not really practical compared to conventional gas cylinders.
Air exhaled from your lungs has a high CO2 concentration, so it might improve growth a bit. But still... does not look practical.
"6 liters of algae water will produce 600 grams of "food" (540 grams is 2500 calories, an average daily food requirement), 600 liters of oxygen, and consume 720 liters of CO2"

What's your oppinion?
 
  • #4
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This does not include any time for the production, nor the required sunlight.
And "liters" is a volume, it depends on the pressure and temperature.
If I assume 600 liters of pure oxygen at standard pressure/temperature, this corresponds to ~1kg. With the additional assumption that the numbers are supposed to correspond to 1 day, it is ~10mg/s and enough for a human. As cross-check: In the same time, the human eats those 600g food, and converts the oxygen back to CO2 (720l are ~1.4kg). Looks quite consistent.
Now, how much radiation and which CO2 concentration do you need to get that?
 
  • #5
This does not include any time for the production, nor the required sunlight.
And "liters" is a volume, it depends on the pressure and temperature.
If I assume 600 liters of pure oxygen at standard pressure/temperature, this corresponds to ~1kg. With the additional assumption that the numbers are supposed to correspond to 1 day, it is ~10mg/s and enough for a human. As cross-check: In the same time, the human eats those 600g food, and converts the oxygen back to CO2 (720l are ~1.4kg). Looks quite consistent.
Now, how much radiation and which CO2 concentration do you need to get that?
To make the world a little easier for you, here is a video:
http://www.youtube.com/watch?v=blPo3X7JhwA&feature=my_favorites&list=FL6rsFVVCgxdG4FOonfjplRQ

The papers from the space agnecy or what ever was saying that 6 liters was enough to keep a man alive, indefinetly.
 
  • #6
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To make the world a little easier for you, here is a video:
That sounds almost insulting. The video never answers the question. Nor does (paraquote) "keeping a man alive indefinitely" answer whether this refers to oxygen or food requirements. In fact I don't see where in the video such a claim was even made at all.

Perhaps the video was just easier for you?
 
  • #7
Drakkith
Staff Emeritus
Science Advisor
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To make the world a little easier for you, here is a video:
http://www.youtube.com/watch?v=blPo3X7JhwA&feature=my_favorites&list=FL6rsFVVCgxdG4FOonfjplRQ

The papers from the space agnecy or what ever was saying that 6 liters was enough to keep a man alive, indefinetly.
Have you considered the difficulty of providing light to the algae, the time it takes to produce the oxygen, the overall difficulty in culturing algae in a closed tank, and other major drawbacks?
It is simply far far easier to use standard pressurized air in diving tanks. In cases where you need air for a longer duration you can use a re-breather. Past that...well you should probably make sure you can come back to the surface before needing more.

Most of the same difficulties apply for uses of algae in space. Perhaps once we have manned spacecraft far away from Earth where they cannot be refueled regularly we will look into this.
 

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