Phytotechnology is the study of plants' processes and their application as practical tools. Understanding their tissues and how they metabolize enzymes helps us understand the environment and apply that logic to creating a better world.
Burns & McDonnell scientist Dennis Haag gets excited about plants. Not because of the flowers or fruit or grain they might produce — he’s interested in what else they can do.
Phytotechnology involves the study of plants’ processes and their application as practical tools. “Plants interact with their environment in a number of ways — transpiration, where materials are vaporized through plant tissues, and metabolism by plant enzymes, for example,” says Haag. “Chemicals are recycled through plants and related organisms living in root hairs and in soils. The process is based on the plant’s habitat, whether that’s in an aquatic system, wetlands or terrestrial systems such as forest or grassland. We can enhance in-situ attenuation of pollutants by designing phytoremediation based on the site.”
Haag used locally available native reed canary grass and mountain willow, planted in an energized soil of his own design, to help remove contaminants from a gasoline tanker spill near the Colorado River. The special soil mix helped certain bacteria flourish, allowing the plants to root and grow rapidly. The plants removed molecules with attached carbons, such as benzene. Some plants accumulate metals — for example, a variety of perennial alyssum concentrates nickel. Others, such as inland salt grass, are useful for their ability to remove chlorides.
Theory in Action
Along with Burns & McDonnell environmental engineer Chris Snider and process engineer Kristin Collier, Haag is putting phytotechnology to work in a new type of constructed wetland designed to treat coal combustion wastes. The project, at Westar Energy’s Jeffrey Energy Center (JEC) near St. Mary’s, Kan., is one of two pilot projects in the United States that will test the use of phytotechnology for treating flue-gas desulfurization (FGD) wastewater.
The JEC pilot project will employ three types of constructed wetlands: free-water surface cells, in which plants standing in water absorb nutrients; vegetated submerged-bed wetland cells, where plant roots extend beneath the soil into subsurface water; and vertical-flow bed wetland cells, in which water flows through a screen of soil and vegetation. The system attempts to duplicate natural attenuation that occurs within created wetlands associated with existing coal storage pile runoff. It will process a blend of water from the Kansas River with FGD wastewater pretreated to remove solids and mercury. The system design includes eight cells in two redundant treatment trains, so that the process can continue when part of the system is shut down for maintenance.
The pilot system is designed to remove elements including sulfur, chlorine, sodium and selenium in order to make the water suitable for surface discharge back to the Kansas River, irrigating prairie hay and tree crops, or for potential reuse in the power plant. Plants used in the system will include inland salt grass, switchgrass, broadleaf cattail, and equisetum, a common plant so effective at removing salts that you can sometimes see salt crystals accumulating in ribbed grooves of the plant’s surface.
The project is unique in that the individual plants will be sampled during the pilot evaluation phase to determine their constituent assimilation and uptake capacities. The plant and soil sampling program is anticipated to allow evaluation of how effective the individual plant species are in removing the constituents of concern in the FGD wastewater.
“Westar Energy is committed to aggressively advancing programs that preserve environmental quality,” says Bill Eastman, Westar Energy’s director of environmental services. “Through this large-scale pilot project, Westar is evaluating a potentially cost-effective, sustainable environmental approach that not only will benefit our own power generation facilities but will advance the coal industry’s understanding of how wetlands can be integrated into a coal plant effluent environmental strategy.”