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Growing a Crop of Algae on Dairy Manure


  The first outdoor test of using algae to clean liquid manure from dairy barns has begun at a U.S. Department of Agriculture research center in Maryland.


Agricultural Research Service microbiologist Walter Mulbry has installed an algae scrubber system near the center's 300-cow dairy barns.


The algae grow in four raceways that are each 50 meters long by 1 meter wide. A similar system is used to treat wastewater from high-density ponds used for fish farming, and on a much smaller scale, in some home aquariums.


For lab prototypes for the full-scale algae scrubber system, Mulbry borrowed small algal turf scrubbers from Walter Adey, director of the Smithsonian Institution's Marine Systems Laboratory at the Museum of Natural History in Washington, D.C. Adey invented the algal turf scrubber as a natural and highly efficient way to clean fish waste from a living coral reef exhibit.


Dairy farmers usually store liquid manure in holding ponds or lagoons and then spray it on field crops. Ammonia escapes into the atmosphere during manure storage and spraying. Phosphorus from field-applied manure can be carried by rain runoff into streams, ponds, lakes, and estuaries, where it can spur excessive algal growth and other associated problems.


Mulbry says that in lab tests the algal scrubbers did a good job of removing most of the ammonia nitrogen and phosphorus from diluted dairy manure.


"Our system eliminates almost all losses of ammonia and nitrate as well as most, if not all, phosphorus losses," Mulbry says. Mulbry tested both raw and treated manure, but the lab results for raw manure are not in yet.


The outdoor tests will check the feasibility of dairy farmers growing algae year-round. The algae will grow on mesh screens lining a series of parallel, shallow raceways. Diluted liquid manure will be dumped at the end of each raceway, flowing in waves down its length.


The algae will be mechanically harvested weekly. The screens will be rolled up and the algae scraped from them.


Once harvested algae could be dried and made into high-protein feed for livestock and fish. Other possible products: fertilizer and high-value chemicals.


To check on the algae's nutritional value, Mulbry will collaborate with animal nutritionists to conduct livestock feeding tests.


Two of the raceways will have a 1-percent slope, while the other pair will have a 2-percent slope, to check the effect of slope and flow on algal production.—By Don Comis, Agricultural Research Service Information Staff.


Walter Mulbry is with the USDA-ARS Soil Microbial Systems Laboratory, 10300 Baltimore Ave., Beltsville, MD 20705-2350; phone (301) 504-6417, fax (301) 504-8370.

"Growing a Crop of Algae on Dairy Manure" was published in the July 2000 issue of Agricultural Research magazine.

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