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The e-mails continue to roll in on the algae issue — and each one seems to bring up another interesting question or observation that was not entirely fleshed out in my story.

For example, one reader did the math and questioned whether there was enough land and oil for all the algae that would be needed to fulfill the nation’s transportation needs. The answer, according to the experts, is plenty.

Researchers estimate that an acre of algae can produce from 10,000 to 15,000 gallons of fuel per year. Given that annual transportation fuel demand in the United States is around 200 billion gallons, between 15 and 20 million acres would have to be set aside for algae. That represents about 2 percent of the 1 billion acres currently dedicated to agricultural use.

But algae farms wouldn’t even take up 2 percent, because it can be grown on land, such as the Salton Sea, that is not suitable for other crops. Same goes for water currently used in farmland irrigation. While algae do need a lot of water to grow, they can grow in just about any water, including salt water and brackish water.

I’ve also received questions about how oil is extracted from algae. The most straightforward way is to dry out the plant and then squeeze the oil out with an oil press. This is similar to the method used by the commercial manufacturers of vegetable oil.

Another option, which can also be used in conjunction with pressing, is to dissolve the algae pulp in chemical solvents and extract the oil through a distillation process. Used together, the pressing and solvent methods will extract about 95 percent of the oil from the plant.

Other, more exotic methods include using enzymes to breakdown individual cells in the algae as well as osmosis and ultrasound.

DAVID WASHBURN

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