Growing Algae on Dairy Manure

By Don Comis
July 20, 1998

Can dairy farms become algae farms? All that manure might grow a lot of algae, according to Walter W. Mulbry, an Agricultural Research Service microbiologist in Beltsville, Md. Mulbry recently began the first lab test to see how well algae remove nitrogen and phosphorus from manure, to keep these nutrients out of streams. He is using treated manure from the ARS Beltsville Agricultural Research Center's 300-cow dairy barns.

In Mulbry's vision, a dairy farm could grow algae year-round on a diet of manure. The algae would grow on mesh mats lining a series of parallel, shallow raceways about 100 yards long. Treated manure would be mixed with water and pumped into the first raceway, flowing down its length. Then it would be pumped into the second raceway, and so on.

Each time the algae grew about an inch, the mats would be mechanically rolled up to harvest the algae. Dried algae could be made into high-protein feed for livestock and fish. Other possible products: fertilizer and high-value chemicals.

Walter Adey, director of the Smithsonian Institution's Marine Systems Laboratory at the Museum of Natural History in Washington, D.C., invented the technique in the 1970's to clean water in the Museum's coral reef exhibit, using fish waste to grow algae. The Smithsonian patented it in 1982.

The technology is now in commercial use in aquaculture and in two wastewater treatment plants. Adey loaned Mulbry a miniature prototype like the one on display at the coral reef exhibit--more a basin than a raceway, measuring 3 feet by 3 feet. Mulbry expects to know in about a month if the system works as well with dairy manure as it does with fish waste and municipal wastewater.

If it does, he proposes building a test raceway outside the center's dairy barns.

Scientific Contacts: Walter W. Mulbry, Soil Microbial Systems Laboratory, Beltsville, Maryland, phone (301) 504-6417, fax (301) 504-7976, wmulbry@asrr.arsusda.gov.