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Growing a Crop of
Algae on Dairy Manure
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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. |
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"Growing a Crop of Algae on Dairy Manure" was
published in the July
2000 issue of Agricultural Research magazine.
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Last Modified: 01/07/2002
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