Smithsonian Yields Dairy Waste Cleaning System

July 26, 2000

An Agricultural Research Service microbiologist has found inspiration to design an algae scrubber system to clean waste from dairy barns in the Smithsonian Institute. Agricultural Research Service scientist Walter Mulbry redesigned and moved a device out of the Smithsonian’s living coral reef exhibit to dairy barns at a research center about 15 miles away in Beltsville, MD.

Mulbry teamed up with Walter Adey, director of the Marine Systems Laboratory at the Natural History Museum in Washington to see if Adey's invention would clean dairy waste as well as it cleaned fish waste. He began with one of the scrubbers that Adey kept in a behind-the-coral-reef exhibit attic space. The scrubbers were algae-lined tanks that filtered water flowing out of, and back into, the coral reef aquaria on public view.

The scrubber did such a good job of removing nitrogen and phosphorus from liquid dairy manure in the lab, that Mulbry recently moved the experiment outdoors. Instead of the scrubber tank, Mulbry used a series of four parallel water troughs, or raceways, each 50 meters long by 1 meter wide. He lined these with plastic mesh for growing algae.

Mulbry dilutes the liquid manure from the dairy barns into tanks at the ends of each raceway, and the diluted manure is then pumped down the raceways in waves. The algae use the manure as fertilizer. Each week, the algae will be harvested by rolling up the mesh mats. The algae will then be dried for testing as a high-protein feed supplement for cattle on the farm and as an aquaculture feed.

The algae will also be tested as a green manure fertilizer to grow corn, soybeans and wheat. Possible commercial uses in the future include high-value chemicals made from the algae.