Making biofuels out of algae has always sounded like a promising idea. In theory, at least, you could create a green alternative to gasoline without any of the drawbacks of corn- or soy-based ethanol (spikes in food prices, increased deforestation, etc.). ExxonMobil's already sinking $600 million into R&D, and a lot of the $80 million that the Energy Department just handed out for biofuels research went toward algae-related projects.

Trouble is, there are still kinks to work out. A new study in Environmental Science and Technology has found, for instance, that turning algae into fuel is an incredibly energy-intensive process—in fact, it does even worse than conventional biofuels on this score. That's mainly because the algae tends to require lots of fertilizer to grow. (Corn and switchgrass, by contrast, can get much of their nitrogen directly from the soil.)

On the other hand, the study doesn't seem like terrible news for algae fuels. For one, algae still doesn't compete with other crops for land, the way corn and soy do. And this is where crop-based ethanols do most of their damage, by indirectly spurring farmers in Brazil and elsewhere to hack down rainforest for farmland. Also, the study has an interesting twist: If you use municipal wastewater to provide the algae with nitrogen and phosphorus, the whole process becomes a lot more efficient. In fact, if you separate out urine from the waste stream and just use that as fertilizer, algae seems to cleanly beat out other biofuels, at least in environmental terms. So in case anyone's looking for useful things to do with wastewater...

Update: As mentioned above, I didn't think this study was all that damaging to the algae cause, but apparently biofuel-makers felt differently: Late on Monday, the Algal Biomass Association fired back with criticisms of the study, claiming that it relied on "decades old data and errant assumptions." In response, the lead author, Andres Clarens of the University of Virginia, said that he was working with the best information out there and that he'd consider doing a follow-up study if companies would make newer data available. We may just get to the bottom of this question yet.

(Flickr photo credit: cjrodkey)