To find a fast, efficient way to clear harmful chemicals along the Gulf of Mexico coastline, researchers are turning to something already familiar with the task – several species of the aquatic grasses and rice that feel very much at home in murky coastal waters.
The research team led by University of Houston's Venkatesh Balan, associate professor of biotechnology in the Cullen College of Engineering's Division of Technology, studies the abilities of these water-loving flora to uptake concentrations of chemicals and heavy metals that unfortunately end up in places where they should not be. Eventually, the researchers also hope to find helpful uses of the system's byproducts.
"But first, we must identify which species are best at removing what we don't want – the chemicals and metals in our coastal water," Balan said. The Managing Urban Runoff project is funded over three years with a $1.5 million grant from the U.S. Environmental Protection Agency, with $624,000 allocated for UH-based research. It is a collaboration of Balan and UH colleagues Xiaonan Shan, assistant professor of electrical and computer engineering, and Weihang Zhu, professor of engineering technology; Ram Ray and Gururaj Neelgund of Prairie View A&M University (PVAMU); and Sandeep Kumar of Old Dominion University in Virginia.
This polluted-water problem stems from a case of too much of a good thing. Heavy rainstorms often wash chemical fertilizers and soil amendments away from the farmlands, lawns and household gardens where they had been helpful in appropriate amounts. Eventually, the runoff accumulates along the Gulf Coast, including in the PVAMU watershed where the team is at work.
"In the process called eutrophication, the chemical fertilizers and soil amendments feed the algae in watersheds. The result is heavy concentrations of excess nutrients such as nitrogen and phosphorus and metal salts such as copper sulfate. That combination feeds cyanobacteria, which produces algal bloom that yields toxins harmful to humans, fish, marine mammals and birds," Balan said.
Removing these substances from stormwater is necessary for maintaining ecological balance and keeping communities healthy.
Other methods of cleaning the water have been proven, including aeration, sprayable clay suspensions, chemical and biological additives, and ultrasonic technology. But they are rarely adopted because of high costs.
Around the world, aquatic plants have long been on the job of reducing nitrogen, phosphorus, heavy metals and fine suspended particles within stormwater runoff, vastly improving the quality of water in the process.
To maximize the natural benefits, selected species of floating aquatic plants typically are nurtured by implanting hydroponically grown native grasses or wetland plants on durable synthetic mats. The plant tissue above the synthetic mat stores excess nutrients. The roots beneath release oxygen and provide a surface to support microorganism growth.
Even in deep or fluctuating waters, this configuration can treat a wide range of wastewater and help restore a healthy population of fish and other wildlife inhabitants. The first key step in the challenge is to select the best species for the task.
"Gasses such as miscanthus, khus and cattail have excellent nutrient removal potential due to their long rooting systems. Rice plants have similar structures and are cultivated as floating aquatic plants in South Asia to remove excess nutrients in ponds and lakes," Balan said. "Once the plants are growing, we can stabilize the water's pH levels by adding artificial aeration to the system, which facilitates the reduction of algae growth."
To get its many benefits, the system requires upkeep, including the regular harvesting of the plants. Also the synthetic mats need to remain properly secured so that heavy winds cannot topple and sink the plants. Balan and the research team are refining a system of grouping the plants and mats by wire, so the clusters can be moved to the middle of the watershed to maximize efficiency then pulled back to the shoreline for easy harvesting.
While the floating aquatic plants currently have no commercial value once harvested, the team is seeking ways to transform the harvested plants into biochar, which has potential to increase organic carbon in soil and other agricultural amendments.
Thanks to the Managing Urban Runoff research team, things are looking brighter – and clearer – along Texas' Gulf Coast.
