Directional Bore, Stormwater Treatment Technologies Solve Problems At Florida Lagoon

By W. Keith McCully, P.E. | June 2009 Vol. 64 No. 6

Only after the canal water is pumped to the Egret Marsh Stormwater Park will treatment begin. In the first treatment step, the water will run across an algal turf scrubber (ATS), which is a very large, gently sloped surface overlaid with a rough grid-like material placed onto a plastic geomembrane. Nutrient-rich water will then flow over the ATS surface where dense mats of algal turf will grow over time to be harvested at a later date. The harvested algae is then composted or mixed with other material and fed to cattle.

The original algal turf scrubber technology was developed by Dr. Walter Adey, director of Marine Systems Laboratory at the Smithsonian Institute in Washington D.C. Its original use was to remove polluted waste from saltwater aquariums. Since then, the ATS system has proven an excellent way of removing nitrogen, phosphorus and a variety of other pollutants found in water and stormwater. The patent for the ATS system is owned by Hydromentia Inc.

Algae harvesting is performed with an all-terrain vehicle or tractor pulling a scraper. The dislodged algal turf will wash into a collection trough and be removed by an automatic rake at a harvesting station. Previous uses of the system have shown that a single operator can harvest up to an acre of algae per hour, resulting in a harvest of about five wet tons. The protein content is generally around 30 percent, making it perfect for reuse as animal feed. Besides using the harvested algae for compost and cattle feed, Egret Marsh will research other uses for the nutrient-rich algae.

After harvesting, the water will move through three interconnected polishing ponds that will remove algal material that escapes the turf scrubber, as well as residual nutrients and remaining solids. Old “borrow” pits will be modified into the polishing ponds and each will hold populations of fish, insects, waterfowl and other animals. The ponds’ water will also provide storage for potential water use by others.

Benefits

Cleaning up the Indian River Lagoon will produce many beneficial effects for the area. A healthier lagoon will increase fish production and recreational activities.

While the recuperation of Indian River County’s portion of the lagoon will be helpful to a variety of parties, the endangered Wood Stork might be getting the most out of the Egret Marsh Stormwater Park. The final polishing pond will be operated and managed to attract the Wood Storks to a safe and well-stocked wetland environment. The only stork that presently breeds in North America, the Wood Stork has small populations in Georgia, Florida and South Carolina.

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