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Algal turf scrubber could benefit Bay
By SEAN CLOUGHERTY
BRIDGETOWN, Md. — Tucked away among corn and soybean fields, the randomly dumping pans of water onto a 150-foot stretch of plastic mesh quickly reveal that there are no waves lapping against a shoreline or pulsing over coral reefs.
But the algae growing there doesn’t know that.
The pans and the mesh are part of an ecological engineered system known as an algal turf scrubber, viewed to have potential in aiding in Chesapeake Bay restoration.
The pans dump water onto the raceway that recreates the pulsing wave energy that exists naturally where algae grows on coral reefs.
The algal turf scrubber technology was developed and patented by Walter Adey, an ecologist at the Smithsonian Institute who studied Caribbean coral reefs for more than 30 years.
In this particular system — installed two years ago on the farm of Bill Collier — water from a ditch on the farm is pumped up onto the plastic mesh in a shallow trough slightly sloped so water flows slowly down it.
The mesh becomes the growing medium for algae which removes nutrients from the water and the water is directed back into the ditch system on the farm.
The algae is periodically removed to allow more to grow and more nutrients to be removed from the water.
The process nearly doubles the amount of oxygen in the water as it re-enters the waterway. The system also operates on solar power running the pump.
The system is part of a research project to study the impact it can have on improving water quality.
Proponents of the system see tremendous potential for cleaning up the bay. Pat Kangas, a University of Maryland environmental engineer who is working on the project said 1,000 acres worth of scrubber systems installed near the headwaters of the Chesapeake Bay could turn over the Bay’s entire dead zone of the Bay in a year.
There’s also the aspect of producing a valued product in the harvested algae. Options for the algae currently being researched include a feedstock for biofuel production, anaerobic digestion, a fertilizer source and a feed additive.
Kangas points to the sustained attention toward green energy and Maryland establishing a nutrient trading program last year as some of the factors that could make the practice an attractive option for Bay restoration.
“This is I think exactly the right time,” he said. “If we can figure out a way to get value out of this algae we will get positive feedback and this thing could take off.”
The system is also being eyed by the Maryland Department of Agriculture as one of many potential practices that could further remediate nitrogen and phosphorus coming from farmland.
John Rhoderick, MDA’s administrator for resource conservation operations, said much of the best management practices for conservation employed on farms focus on managing surface runoff.
But in some places in Maryland, Rhoderick said as much as 70 percent of the nutrients entering waterways comes from the ground water.
“We’ve got a lot of BMPs and farmers are good at managing the nutrients that come off the surface,” Rhoderick said. “But it’s still a leaky system, so what do you do when it escapes?”
To address the groundwater issue, several practices, from floating wetlands to phosphorus-sorbing ditch filters to algal turf scrubbers are in various stages of research.
“It becomes for us this suite of practices and the algal turf scrubber is an exciting part of that,” Rhoderick said. “It’s another tool in the toolbox.”
The agriculture department however, is cautious at this point to deem the system a best management practice until more precise and quantifiable data is attained verifying the nutrient removal capabilities and begin to solidify its value on the nutrient credit trading market.
Kangas said nutrient removal from this and other scrubber systems that have been studied around the Bay extrapolate to ranges of 670 to 2,000 pounds of nitrogen and 70 to 200 pounds of phosphorus on a per acre per year basis.
He estimates the system on the Collier farm ranges in nutrient reduction from 20 percent to 60 percent from the top to the bottom of the system, but he added that doesn’t give an accurate picture because it only measures one point in time, rather than a complete harvest cycle.
He said he hopes to have continuous monitoring equipment installed which would produce a more accurate removal rate.
“We are very interested in comparing this number with the known amount of nutrient removal, described with the equation given above, in order to better understand the biogeochemistry of the algae production systems,” Kangas said.
With all its potential, the system is not without obstacles, particularly land and money.
“For a system like this, you need to have a lot of land,” Kangas said.
Kangas said he would like to see thousands of acres covered with scrubber systems in about 10 years.
Hopefully by then, he said the process to use the algae for butanol production will have advanced enough to be scaleable and the fuel will have a market. For now, he said he’d settle for a system about an acre in size in a production setting that can also be studied.
Just like other practices being studied, the algal turf scrubber isn’t the best fit in all cases.
Rhoderick said the department has identified “hot spots” in the state where nutrient movement in groundwater is high.
From there, sites can be identified where there is sufficient water flow during the nine-month stretch when algae can grow.
“You’ve got to find a place where it makes sense to use it and you’ve got to have access to the water,” Rhoderick said.
Cost could also be a hurdle for landowners considering a scrubber system depending on the return from selling nutrient credits and the value realized from the harvested algae.
When the system was installed on the Collier farm two years ago, Kangas estimated the cost per acre at $75,000 though he said the cost of some of the materials has decreased since then.
Kangas also said he’s “real close” in being able to justify the cost of a system just through the sale of nutrient credits.
Even if the technology takes a while to be adopted on a wide scale, Kangas said the most likely place is in the Bay watershed.
“The thing of this is the Chesapeake Bay is a focal point. The first kinds of these solutions is going to come out of this area,” he said.