Manure Manager

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Algae advances as alternative for improving water


June 2, 2010
By Manure Manager

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Algae – already being eyed for biofuel production – could be put to use right away to remove nitrogen and phosphorus in livestock manure runoff, according to an Agricultural Research Service (ARS) scientist.
Algae – already being eyed for biofuel production – could be put to use
right away to remove nitrogen and phosphorus in livestock manure
runoff, according to an Agricultural Research Service (ARS) scientist.

algae-02
Analysis of air-dried algae from an algal turf scrubber shows that the algae captured most of the nitrogen and phosphorus in the manure. With additional processing, the dried algae could be sold as a slow-release organic fertilizer or as an animal-feed supplement. Photo by USDA-ARS


That could give resource managers a new eco-friendly option for
reducing the level of agricultural pollutants that contaminate water
quality in the Chesapeake Bay.

Microbiologist Walter Mulbry works at the ARS Environmental Management and Byproduct Utilization
Research Unit in Beltsville, Md., which is located in the Chesapeake
Bay watershed. In 2003, Mulbry set up four algal turf scrubber (ATS)
raceways outside dairy barns in Beltsville. The shallow 100-foot
raceways were covered with nylon netting that created a scaffold where
the algae could grow.

For the next three years, from April until December, a submerged water
pump at one end of the raceways circulated a mix of fresh water and raw
or anaerobically digested dairy manure effluent over the algae. Within
two to three weeks after the ATS system was started up every spring,
the raceways supported thriving colonies of green filamentous algae.

Algae productivity was highest in the spring and declined during the
summer, in part because of higher water temperatures and also because
the raceways provided snails and midge larvae ample opportunity to
graze on the algae.

Mulbry and his partners harvested wet algae every four to 12 days,
dried it, and then analyzed the dried biomass for nitrogen and
phosphorus levels. His results indicate that the ATS system recovered
60 to 90 percent of the nitrogen and 70 to 100 percent of the
phosphorus from the manure effluents. They also calculated that the
cost for this capture was comparable to other manure management
practices – around $5 to $6 for each pound of nitrogen that was
recovered and around $25 for each pound of phosphorus that was
recovered.

Results from this research were published in Bioresource Technology.

Read more about this research in the May/June 2010 issue of
Agricultural Research magazine, available online at:
http://www.ars.usda.gov/is/AR/archive/may10/algae0510.htm.