Conceptually, algae farming is simple as framed by Isaac Berzin of Greenfuels. Here's the bioreactor at MIT.


Bioreactors will be co-located with power plants that emit CO2 (carbon dioxide). The CO2 must be sequestered at the plant and fed as an input to the algae farm. From Berzin:

Actually, in professional terms it's called a bioreactor. It's nothing but three tubes connected together with some sea water and algae in them. And you can see the bubbles bubbling through the system. And you can kind of look at the bubble and follow it, and in the ten seconds or so that the bubbles are spending in the bioreactor 80 percent of the CO2 is moved and 85 percent of the NOX [NO2]. And at the end of the day you harvest the algae, whatever was growing during the day, you take out of the system. It's like a cow you milk it and you make biofuels from the algae.

Sounds pretty good, doesn't it? In fact, the interviewer Bruce Gellerman thought it sounded too good to be true.

GELLERMAN: So, I was taught, you know, if it sounds too good to be true it usually is. What am I missing?

BERZIN: I'll tell you what the problem is. You have to produce algae in a cost that will be cheap enough to compete with fossil fuels. Then you think, wait a minute, what does this technology need? It needs land, and you need water, and you need CO2. So, CO2 is not an issue. You're located next to a CO2 generating facility. Water, you get to use any quality of water. Treated sewage water, brackish water, ocean water, any water available. The third thing is, the land, usually near these big power plants, no one wants to live. It's non-fertile land, nothing grows there even. So, you don't really compete with agriculture. So, how realistic this is? We believe it is realistic.

So, the process requires CO2, water and some unused land. Not competing with agriculture is one of the stronger points supporting bioreactors, as Olivier Danielo notes

The production of traditional biofuels requires expansive land surfaces for cultivation. Terrestrial biofuels come traditionally from two sources: oil, produced from sunflower or rapeseed, and alcohol, produced from the fermentation of sugars from beets, wheat, or corn.

The production of these biofuels necessitates the use of large tracts of land. According to Jean Marc Jancovici, an engineer specializing in greenhouse gas emissions, it would require a sunflower field 118% the size of France to replace the 50Mtep of petroleum consumed each year by the French for their transportation needs (104% of the size of France for rapeseed, 120% for beet, 2700% for wheat).

Oil from algae requires less land but as Gellerman notes, "theoretically, if you created an algae bioreactor twice the size of New Jersey, you could supply the entire petroleum needs of the U.S". So, there's still a small land problem in replacing our fossil fuels with biofuels from algae farms. And of course, bioreactors are not a panacea that frees us from CO2 emissions. Yes, most of the CO2 (and NO2, another greenhouse gas) is captured at the power plant and consumed by the algae. The resulting biofuels can be "used to run engines, or converted into methane or fermented into alcohol". But there is still a problem of course because CO2 will be released into the atmosphere via downstream tailpipe emissions.

This subject first came up at TOD months ago in a few comments I can't find. A recommended resource advocating producing biodiesel from algae is the UNH Biodiesel Group (University of New Hampshire). This topic also came up in some comments by ericy and joule in response to a previous post Weyburn, CO2 Injection and Carbon Sequestration. You can find out more about what NREL is up to here.

On the whole, using pond scum to decrease CO2 emissions (at least at power plants) seems like a good idea. Harvesting eukaryotic algae doesn't put us in much spiritual jeopardy, right? If the technology was intensely used internationally, we wouldn't have as much to worry about when it comes to this guy.

Smokestack emissions bubble through algae-filled tubes at MIT's Cogen plant (from LOE)

This high-tech farming doesn't solve all our woes but it's certainly better than nothing.