November 2015 Vol. 70 No. 11


Green technology emerges for stormwater management

A new green technology has shown great potential for stormwater management – research efforts have shown potential for the use of floating treatment wetlands (FTWs) to remove nutrients and contaminants from stormwater retention ponds.

FTWs float on the surface of wet ponds and provide a growing medium for emergent wetland plants, with floating mats or rafts built to support vegetation grown hydroponically. The plant stems are above water level, with the roots below the surface, allowing plants to gain nutrients from the water column.

At Virginia Tech, David Sample, associate professor and extension specialist with the Department of Biological Systems Engineering, tested FTWs at demonstrations in Fairfax and Virginia Beach, VA, and investigated the ability of the systems to enhance nutrient removal in wet retention ponds.

Sample concluded that FTWs could provide a way to meet total maximum daily load (TMDL) reductions, but that quantifying an appropriate number reduction credit is still problematic.

Active research is ongoing for evaluating the reduction, and the U.S. EPA Chesapeake Bay program has developed an expert panel to consider how credits will be allocated when using FTWs, Sample added.

Researchers from the Department of Biological and Agricultural Engineering at North Carolina State University (NCSU) in Raleigh contend that FTWs could become a popular retrofit due to their potential to enhance the nutrient removal capacity of thousands of wet retention ponds across the U.S.

According to the researchers at NCSU, FTWs are a great retrofit option because they do not require earth moving, as well as their ability to eliminate the need for land to be dedicated to the treatment process.

The NCSU-led study included staggering the placement of FTWs in the retention ponds, which proved important for impeding stormwater movement and increasing retention time. The placement was also critical in helping to increase the pollutant uptake by the root systems.

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