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It is necessary to have extra source of CO2 i.e. from a nuclear reactor or factory chimney to produce bio-fuel by microalgae or is it able to do it with the normal CO2 density in the atmosphere?

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I think your question needs some clarification to be answerable. Algae need $CO_2$ as a carbon source for photosynthesis but the source is irrelevant. Are you asking if industrial scale biofuel production can be sustained at atmospheric $CO_2$ concentrations? –  KennyPeanuts May 9 '13 at 12:36
    
@KennyPeanuts: Exactly. Is it possible to produce bio-fuel from micro-algae at industrial scale at atmospheric Co2 concentrations? –  Xaqron May 9 '13 at 13:09
    
That is definitely an interesting question but I am not sure it is a biological question as much as an engineering question. –  KennyPeanuts May 9 '13 at 14:53
    
I asked this because it is claimed to change the world by providing green fuel, but if it needs high concentration of Co2 then it cannot exist in a complete green world (needs pollution for existance) –  Xaqron May 9 '13 at 14:57
    
OK so that sounds like a slightly different question... it sounds more like you are asking if algal biofuel production could lower atmospheric $CO_2$ concentrations to the point where it is no longer possible. I think the issue here is that the industrial process that "farms" the algae could concentrate the $CO_2$ in the bioreactor so that the atmospheric $CO_2$ concentration isn't that important. There was certainly lots of algal production when atmospheric $CO_2$ was 280 ppm, so that is plenty to get them to grow. –  KennyPeanuts May 9 '13 at 15:06
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up vote 2 down vote accepted

Maybe this is easiest understood comparing to our current rate of CO2 consumption to the possible industrial CO2 absorption rate.

Human non biological CO2 production is 29 Gtons. A little more than four tons of carbon per human being each year. The natural carbon cycle on the planet through CO2 is otherwise about 788 Gtons.

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Is it possible to grow enough algae to balance our current rate of industrial production? I think so - it would be an additional 2% of the current carbon cycle. In a first pass, that implies turning 2% of the non-productive earth surface into an average patch of ocean or forest/jungle.

This is possible, but it would be expensive. we're talking about flooding a desert basin for algae production. (numbers are from google).

2% * (area of earth surface = 197million miles^2) = 3.9 M miles^2.

Sounds doable, but remember that 70% of the earth's surface is already water and producing algae at a pretty good clip. We'd be using ~6% of all the land for the algae farm:

For comparison, 3.9M miles^2 is larger than the continent of Australia. (2.97 Million miles ^2), and bigger than the Sahara desert (3.6 M miles^2).

just to get into the questions raised in the comments.... To DEPLETE the CO2 level in the atmosphere, we'd have to produce more fuel from the algae than we use - which seems to be impractical from a market standpoint - the fuel would be sitting around in warehouses while the plants die. I can't imagine anyone making any money from this, and it would be expensive... so it'd be a strange set of circumstances that would deplete the atmosphere from carbon dioxide. Also more oxygen probably would encourage more combustion and more animals too... so hard to see this happening.

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Amazing answer. This is not my field of specialty but listening at a conference, the bio-fuel plants were planned to be near factories and nuclear reactors to use their extra Co2, so I was curious to know, if we produce enough bio-fuel then there would be no need for reactors/factories and is it possible to continue producing bio-fuel without these source of pollutions or bio-fuel plants get shutdown. –  Xaqron May 9 '13 at 20:44
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nice answer.... –  WYSIWYG May 9 '13 at 21:11
    
Thanks, both! I think we'd still need power plants to convert the biofuel to energy (unless its bioelectricity or biohydrogen). With a projected population of 12 billion, demand for fuel is just going to go up. I think they were saying that from the plants/factories you can pump the CO2 directly into the pools of algae. I'd like to see numbers on how this might prevent the CO2 from getting into the atmosphere. Could help... we used to bubble CO2 into the algae in the lab to help it grow. I would be surprised if it changed the efficiency of an effort this size by more than a few %..? –  shigeta May 9 '13 at 21:57
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