Algae
advances as a 'green' alternative for improving water
quality
Close-up of algae growing on an algal turf scrubber. Although
the types of algae that grow in algal turf scrubbers are dominated
by only one or two species of filamentous green algae, the biomass
contains dozens of native algal species. Since different native
strains of algae are adapted to thrive in all types of fresh,
brackish, and salt water, algal turf scrubbers could potentially be
used in a range of settings. Photo by © Edwin Remsburg.
Friday, May 7, 2010
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. 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.
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United States Department of Agriculture-Research, Education, and
Economics
Thanks to United States Department of Agriculture-Research,
Education, and Economics for this article.