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Process Turns Algae into Renewable Fuel, Cleans Wastewater

Pond with algae (Higetiger/Flickr)Chemical engineers at University of Arkansas in Fayetteville have developed a method for converting common algae into butanol, a renewable fuel that can be used in today’s internal-combustible engines. The technology has the added benefit helping to clean and oxygenate U.S. waterways by removing excess nitrogen and phosphorous from fertilizer in agricultural runoff.

The team of engineering professor Jamie Hestekin and students discovered a more efficient fermentation method of growing algae on troughs made of screens or carpets, measuring two feet wide and ranging from 5 to 80-feet long, depending on the scale of the operation.

The researchers harvest the algae every 5 to 8 days by vacuuming or scraping it off the screens. The researchers then crush and grind the dried algae into a fine powder to extract carbohydrates from the plant cells. They treat the carbohydrates with acid and then heat them to break apart the starches and convert them into simple sugars.

The researchers then begin a two-step fermentation process. The first step turns the sugars into organic acids: butyric, lactic, and acetic. The second stage uses a process called electrodeionization, a technique developed by one of Hestekin’s doctoral students. This technique uses a membrane that separates the acids during the application of electrical charges. By quickly isolating butyric acid, say the researchers, the conversion process becomes easier and less expensive.

Butanol, says Hestekin, has several advantages over ethanol, the current primary additive in gasoline. Butanol releases more energy per unit mass and can be mixed in higher concentrations than ethanol. It is also less corrosive than ethanol and can be shipped through existing pipelines. And unlike corn, the current main ethanol feedstock, algae are not in demand as food.

Algae live on nitrogen, phosphorous, carbon dioxide, and natural sunlight, so the researchers grow algae by running nitrogen- and phosphorous-rich creek water over the surface of the troughs. They enhance this growth by delivering high concentrations of carbon dioxide through hollow fiber membranes.

Municipal and state governments, primarily on the East Coast of the U.S., have implemented similar processes on a large-scale to address “dead zones,” where excess nitrogen and phosphorous from agricultural runoff have killed fish and plants. Hestekin’s team is currently working with the New York City Department of Environmental Protection to create biofuel from algae grown at the Rockaway Wastewater Treatment Plant in the borough of Queens.

Read more: Univ. Engineers Develop New Sewage Treatment Device

Photo: Higetiger/Flickr

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