Wednesday, February 18, 2009

Oxygen From Algae,tx14_paul,blog,999,All,Item%20not%20found,ID=090112_2598,TEMPLATE=postingdetail.shtml

The bulk of our oxygen is made by algae, and for a life support system in closed space algae would probably be ideal. A study done in the 60's about using algae to determine the feasibility of using algae on nuclear subs. The fact that it isn't used probably has more to do with the fact that the two things a nuclear sub has plenty of is energy and water, which make electrolysis ideal. For something like a permanent off Earth base though water and energy will probably be in short supply.

The study found that you could get 4.5L/hour from 6.2L of algae and 34k footcandles of light (from 9kw worth of incandescents). It is unclear what 6.2L is actually a mesurment of. It could be just the water used, or the entire volume of the whole apperatus. Also they refer to it as a "small pilot plant", which could even mean it was 6.2L worth of seed algae which further grew. I'm just going to assume it's 6.2L worth of water and algae. Also it's worth noting that 9kw worth of incandescents is a lot of engery. Some newer form of light production would be more effecant, however it's unknown what type of incandescents they were using. Higher wattage bulbs are more effciant than lower ones, so a 1.5kw bulb would be much more efficient than a 100w. So it would be inaccurate to simple find how much watts florecnts would need to match a 100w. Also the most efficient form of light we have is incandescent, sodium vaper lights (street lights), which they very well could have been using. Since we have foot candles we know how much actual light we need, however foot candles aren't used very often, and can't be directly converted into lumens.

A random site claims a healthy resting adult uses 53L of oxygen per hour. However, I noticed what I think is a flaw with their estimate. If you follow their steps to arrive at the 53L number it is clear that is the ammount of oxygen breathed in during an hour. However, only about 19% of oxygen is used in any breath. Thus the ammount of oxygen needing to be replaced during an hour would be closer to 10L. Also you may remember that I said generally if you are in an enclosed space CO2 buildup is what will kill you before lack of oxygen does. I'm assuming that if the algae is generating all the oxygen you need it will also be using all the CO2 you give off. Lastly we probably don't want to assume constantly at rest healthy adults. I found that the breaths per minute rate goes up by about 3 during exercise, so I'll use 30L as the ammount need per person per hour. Since you won't be exercising 24/7 this should be a good safty margine too.

To get 30L from algae we'll need to scale up the above study by 6.66, round up to 7 that means we'll need 44L of algae, 238k footcandles, which 63kw worth of incandescents could provide. 44L isn't very much space, a cm deep square meter is 10L, so 4.4 of them. 63kw worth of engery is a lot though, a large house probably uses no more than 5kw. Doing some searching I've found numbers that seem to indicate getting that much light for about 30kw. 100 people would require 6.3mw using these numbers. Small nuclear reactors used in civilian ships out put about 150mw, the ISS seems to generate about 110kw. It's also worth noting that any given spot on the moon will receive full sunlight for 15 days straight, then 15 days of darkness. Also there is talk about placing a base in a crater near the poles, which due to it's angles would receive full sun 24/7 (usefull for solar power, but also would be ideal for plants). Lastly sunlight on the Moon would be more intense than on Earth, due to the lack of atmosphere.

No comments:

Post a Comment