Quote Originally Posted by farothel View Post
That's why I mentioned algea. They can be grown in a much smaller volume, although they wouldn't give the same morale effect as other plants.
They also have the issue of getting the CO2/O2 in and out of solution, along with the significant infrastructure involved - a 1 cubic metre bioreactor will weigh 1 tonne for the water alone, before factoring in the vessel, algae and other infrastructure. A separate issue is engineering - you have to put specialised daylight wavelength bulbs in at regular intervals due to the limited penetration of light through water and the physical blocking effects of the other algae.

This page indicates that an algae pond of 3600 acres can capture 80% of the daily CO2 emissions of a 200MW natural gas power station during daylight hours (assuming a population density of 20g dry weight algae per square metre).

This report indicates that gas powered power plants emits 348kg CO2 per MWh, so:

200MWh x 348kg CO2 = 69600 kg CO2
69600 kg CO2 x 80% = 55680 kg CO2 per 3600 acre
55680 kg CO2 / 3600 acre = 15.4667 kg CO2 per acre
15.4667 kg CO2 per acre = 0.0038 kg CO2 per square metre = 3.82 g CO2 per square metre

Assuming 50% availability of O2 for human use and no losses in getting it out of solution:

3.82 g CO2 / square metre * 50% = 1.91 g O2 per square metre

From above, an astronaut need 840g O2 a day so:

840 g / 1.91 g per square metre = 439.9 square metres of algae at a concentration of 20g dry weight per square metre.

Considering that daylight doesn't penetrate much more than 1 metre in fresh water (link), that's basically 440 cubic metres per person. I don't think algae can be used without some very clever engineering.