Treating nutrients with algae
With all the bad press about algae, we often forget that it really can be beneficial. In fact, algae are responsible for much of the air we breathe, and they form the base of the food web upon which all life depends.
I suspect most readers are aware that algal blooms often occur when too many nutrients enter our waterbodies. With this understanding, a novel approach was developed and patented in 1980s, by Dr. Walter Adey at the National Museum of History, to remove nutrients from a waterway by running the water across a shallow trough or raceway upon which attached filamentous algae are allowed to grow. The algae treat the water by taking up nutrients, primarily nitrogen and phosphorus, as they grow.
Where does the algae come from? Provide the right conditions – sunlight, water and nutrients – and algae will establish naturally. What grows is the same green filamentous algae we often see attached to rocks and seagrass in shallow areas. Only in this case instead of being a nuisance, it’s beneficial.
Periodically, once or twice weekly, the nutrient-fed algae are harvested. Harvesting the algae not only removes nutrients (and other pollutants), but it also leads to higher growth rates for the algae remaining, because thinning reduces competition for light and nutrients.
As the treated water exits, it is often directed to polishing ponds or treatment wetlands where the water continues to get cleaned before exiting the system. The technology I’m referring to is known as an Algae Turf Scrubber (ATS).
Because of the fast growth rate of algae on the ATS, this technology can remove nutrients at a high rate. In fact, biomass production rates of ATS are among the highest of any recorded values for natural or managed ecosystems.
ATS in Florida
One doesn’t have to go too far to see an ATS in action. Egret Marsh Stormwater Park and Wildlife Sanctuary in Indian River County utilizes this technology to removed dissolved nutrients from a drainage canal before it enters the Indian River Lagoon.
Approximately 10 million gallons of water are treated by this 4.6 acre “algae farm” every day. Annually approximately 32,000 pounds of total nitrogen and 3,000 pounds of total phosphorus are removed by the ATS from canal water that would otherwise enter the Indian River Lagoon. Thirty plus additional acres of polishing ponds and finishing wetlands further treat the water and create a haven for wildlife that has become a favorite spot of the birding community.
Of course, there are some challenges with this type of system. First, it requires land, people and equipment, and second, the algae biomass must go somewhere. Currently, Indian River County sends their biomass to the landfill. Interestingly, the University of Maryland has been exploring different uses for ATS biomass including as a filler for concrete and as algae fire logs. Where they see the greatest potential however is in health products.
Algae Turf Scrubbers have been tested in a number of locations and for a number of land uses ranging from agricultural to urban with good results. A company called Hydromentia, headquartered in Ocala, is currently working on commercialization of the ATS technology. And, a new in-water algal production system has recently been developed that utilizes an attached algal community growing on screens that are suspended in a waterway from a floating platform.
With all the talk about algae and nutrients in the state, maybe we’ll be seeing more of these ATS in other Florida locations soon.