Algae Ponds: the lovers and the haters
This week’s issue of C&EN includes some news from algae-based biofuels firm Sapphire Energy. The company is reporting its first harvests of algae biomass from a large, outdoor algae farm in New Mexico.
Sapphire has grown and gathered 21 million gallons of algae biomass totaling 81 tons. Eventually, the plan is to make a kind of crude oil from the algae. They grow the stuff in very large outdoor ponds. According to the press release, “the cultivation area consists of some of the largest algae ponds ever built with groupings of 1.1 acre and 2.2 acre ponds which are 1/8 of a mile long.”
You’d think that the promoters of algae for biofuels would be clinking glasses filled with spirulina-enhanced juice at the news. But you’d be wrong.
In fact, a trade group of algae firms calling itself the National Algae Association says the kind of ponds used by Sapphire – known as raceway ponds (you can see why looking at this image) – will not scale up commercially. Instead the NAA supports the development of photobioreactors (PBRs for short). Similarly, algae researcher Jonathan Trent, writing in a New Scientist magazine piece that also appears in Slate is arguing in favor of photobioreactors. Specifically, Trent says PBRs should be deployed offshore. I’ll quote from his article where he summarizes the raceway/PBR tradeoffs:
Sapphire's outdoor raceway ponds in New Mexico. Source: Sapphire Energy
There remains the question of how and where to grow the algae. A few species are cultivated commercially on a small scale, in shallow channels called raceways or in enclosures called photobioreactors (PBRs). Raceways are relatively inexpensive, but need flat land, have lower yields than PBRs and problems with contamination and water loss from evaporation. PBRs have no problems with contamination or evaporation, but algae need light, and where there is light, there is heat: A sealed PBR will cook, rather than grow, algae. And mixing, circulating, and cleaning problems send costs sky high.
Trent doesn’t mention what industry analysts complain about the most. When it comes to algae, though PBRs might be the best bet, they require too much capital expenditure for the equipment.
Meanwhile, Solazyme, which started life as an algal fuels firm but now is manufacturing oils for use in skin cream and other high value applications, grows its algae in a third way – its algae live in bioreactors, but in the dark. They eat sugar and make oil. Is there a best way to commercialize algae for fuels and chemicals? Is there any way? It seems that it is still too early to tell.