If I wanted to live below the surface of water, how large cultivation of plants would be needed to ensure enough breathing air and to neutralize carbon dioxide?
How much light is blocked 30 feet below surface? Practical issues to consider before moving down below?
From personal experience I can say that at 30 feet a lot of red is gone and at 100 feet all that is left is something between blue and indigo. There is plenty of light to see with at 100 feet but I suspect that most plants we are used to won’t grow much below 30 feet. No cite just a guess.
The order in which light is absorbed is “Roy G Biv” with the first letter of the color matching the letters in the name.
Seagrass meadows can grown up to 300ft below the ocean and the depth they can grow at depends mainly on the attenuation co-efficient of the water. Obviously sea grasses that grow at this depth must have evolutionary adaptations to allow them to grow in such little light, but there are land-based angiosperms that can grow in low light, for example the few plants that grow on the floor of the rain forest.
while a plant may grow with light at that depth it would have to grow at a certain rate to be useful.
However, you’d never have to mow the lawn or rake leaves, so it’s all good.
If I did not have to worry about light (I can use LEDs), I’d still be happy to know some numbers of the gas economy. Wikipedia says that you need no more than 1-6l of oxygen/min.
http://en.wikipedia.org/wiki/Rebreather
NASA did some work on this in terms of supplying oxygen to astronauts. They used electric light and hydroponic growing trays, with plants selected for oxygen production. If memory serves, there was something like 20-30 square meters of growing space required, but using hydroponics and artificial light means that you could stack growing trays on top of each other for something that would fit into a cube 3x3x3 m or so.
This is probably your best bet under that much water unless you envision a way to have acres of growing space.
I’d have thought it might be easier just to perform gas exhange with seawater - maybe some sort of spray-fountain fed by pumped-in fresh seawater (falling into a collection tray and pumped back out again)
If you’re just 30 feet below the surface couldn’t you just get a 50ft pipe with a pump through your roof for oxygen?
How many 10w R&B LEDs would be adequate for 30 sqft? What about decompression sickness or other medical issues?
Sorry 30m2 that is…
If, for some reason, you want a completely sealed unit, then the only answer is “you need to produce all the food that you eat”. Your gas budget is almost entirely dependent on the food you consume. If you are importing food into your unit, then you’ll need an infinitely large volume of plants because you are constantly importing food, which is a carbon dioxide source and a oxygen sink. So long as you keep bringing in food from the outside your garden will need to keep getting larger and larger.
The only simple solution to that is to start dumping waste into the ocean. But if you have no problem with an open system ,then if you just want to “ensure enough breathing air and to neutralize carbon dioxide” then you wouldn’t use plants at all. You would just set up an artificial gill, excreting excess carbon dioxide directly into the water and absorbing oxygen. Much more energy and space efficient than trying to use plants to do the job.
Of course, if you are only 30 feet below the surface, one would have to question why you wouldn’t just pump air down to your building. Even if you don’t want to pump air down, it would make more sense to pump an algal solution *up *to the surface in transparent pipes, then to try to get light *down *to land plants anchored inside the building.