New Scientist | Tech | Environment | 12 July 2010
Pond scum. The term surfaces in every news report about the decades-long effort to get energy from algae. But more respect for the tiny creatures may soon be in order: industry and governments have started pouring billions into alga power.
Just the basic facts make you wonder why algae aren't powering our civilisation already. The single-celled phytoplankton produce half our planet's oxygen and are the fastest-growing green organisms known. In shallow seawater ponds on land, they can use sunlight and sewage to turn concentrated carbon dioxide – flue gas from coal burning, say – into usable hydrocarbons, half of which can almost be poured straight into a diesel engine.
"Ten million hectares of algae could supply all US transportation fuel," says Greg Mitchell of the Scripps Institution of Oceanography in La Jolla, California. That's less than 3 per cent of the area farmed in the US – and algae can live in seawater in the desert.
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Energy efficient - Algae can produce 10 times as much energy per hectare as land-grown oil crops, says Mark Hildebrand of Scripps, because "they float. They don't have to spend half their [energy] building stalks to support themselves."
Instead, they make more cells until they run out of nutrients such as nitrogen. Then they stop dividing, but keep photosynthesising, storing the results as an oil droplet that can eventually take up more than half the cell.
One simple chemical reaction makes this oil into a diesel fuel that releases less particulate, sulphur-oxide and nitrogen-oxide pollutants than petroleum-based diesel. The remaining algal biomass can also be burned as fuel, though may be worth more as livestock feed, especially for fish. That means less damage to the environment, and less demand for overtaxed fisheries, soil and water to catch or grow feed.
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A little means a lot - And ultimately, production will require suitable climate, land, water, nutrients and CO2, all at one site. Even using waste land, seawater, sewage and smokestack CO2, Benemann thinks this will limit the potential for algal biomass to the equivalent of 1 per cent of the CO2 now being released, or less. "But that's still a gargantuan amount. Let's hope we can do that much."
We won't without more long-term funding, says Mitchell. But he is sanguine about the pay-off. "The US has been subsidising corn ethanol at $5 billion a year. Half that amount for 15 years in algae could solve the water, fuel, energy, feed and farmland crises humanity faces."