Question for the phycologists among us

[XemaSab]

Could waste CO2 be bubbled through a tank to encourage algal production? Or would it do nothing to foster growth? Or even inhibit growth?

Thanks. :)

[physioex]

1. Not a phycologist...

But I did watch a show on Discovery Science where a researcher was working on growing algae from the CO2 of coal plants.

[Ezlivin]

2. According to this web page, it appears not

Mixing is necessary to prevent sedimentation of the algae, to ensure that all cells of the population are equally exposed to the light and nutrients, to avoid thermal stratification (e.g. in outdoor cultures) and to improve gas exchange between the culture medium and the air. The latter is of primary importance as the air contains the carbon source for photosynthesis in the form of carbon dioxide. For very dense cultures, the CO2 originating from the air (containing 0.03% CO2) bubbled through the culture is limiting the algal growth and pure carbon dioxide may be supplemented to the air supply (e.g. at a rate of 1% of the volume of air). CO2 addition furthermore buffers the water against pH changes as a result of the CO2/HCO3- balance. Depending on the scale of the culture system, mixing is achieved by stirring daily by hand (test tubes, erlenmeyers), aerating (bags, tanks), or using paddle wheels and jetpumps (ponds). However, it should be noted that not all algal species can tolerate vigorous mixing.
Algal Production

[izquierdista]

4. I think you are misreading

The phrase "CO2) bubbled through the culture is limiting the algal growth" means that CO2 is the limiting factor in the growth of the algae. This is not surprising, since it is well know that increases in ambient CO2 cause increases in rates of photosynthesis.

If any of you DUers are interested further in this, I am looking into developing some pilot plant studies in this technology. E-mail me and let's collaborate.

[Ezlivin]

6. No way!

:)

Actually I saw that the use of CO2 was a positive factor but that the introduction of too much would be disruptive.

I assume from the discussion that the interest in algal growth centers about its usage in biofuel production. Correct?

[izquierdista]

8. What's too much..

Too much of anything can be harmful, but the article you quote suggests raising the CO2 level from the ambient 300 ppm to 1% (or 10,000 ppm) which is well within reason. At levels above 1% you are probably going to lower pH and adversely affect the carbonate/bicarbonate equilibrium. It is helpful to remember that plants evolved in an environment containing from 300 to 800 ppm of CO2 in the atmosphere, so their optimal growth should be somewhere in that range.

Yes, algae is a promising source of biofuel, the problem being that it is only recently that any work has been done on how to commercially cultivate algae. Spirulina is probably the only variety of algae that is grown and harvested under artificial, human controlled conditions. Its importance is as a protein source, though, not as a source of lipids for biofuel.

Adding CO2 is not the ultimate solution to growing algae however. In the open ocean, the limiting factor for algae growth is Fe++. There have been proposals bandied about to seed areas of the ocean with iron to enhance algae growth and stimulate the bottom of the food chain. If you saw Al Gore's movie, there was the slide that shows the oscillation in CO2 levels consistent with algae blooms in the oceans -- stimulating massive algae blooms is one thought of how to counteract the rise in global CO2 levels. This is one idea where I would advocate a conservative position; try it on lakes and inland seas and characterize it well before doing it with large areas of the Pacific Ocean.

[XemaSab]

11. Either biofuels or sequestration

Both would be useful.

[jpak]

3. If it was used to maintain saturated dissolved CO2 concentrations in cultures - yes

But dissolved inorganic carbon (DIC) - by itself - doesn't necessarily stimulate growth in phytoplankton...

[XemaSab]

5. I'm confused

How can carbon be inorganic? :shrug:

Lack of hydrogen? :shrug:

[eppur_se_muova]

7. CO2 and carbonate (CO3=) are regarded as inorganic. nt

(As are metal carbides, but not relevant.)

[XemaSab]

9. (putting my C in O-chem to the full test)

:P

[OKIsItJustMe]

10. Play Video #3

Here:
http://www.pbs.org/saf/1506/video/watchonline.htm