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Seminar: Plasma-based water treatment of perfluoroalkyl substances: reactor design challenges and physicochemical processes at the plasma-liquid interface
October 11, 2018 @ 4:00 pm - 5:00 pm
Dr. Selma Medadovic-Thagard
Plasma-based water treatment (PWT) utilizes electrical discharge plasmas formed in contact with or in the vicinity of water to degrade chemicals within contaminated water. Plasma in these conditions is capable of producing a diverse range of highly reactive species with relatively low energy input and without chemical additives, which makes PWT a promising alternative treatment technology that has inspired decades of investigation and development. Despite the obvious benefits and advantages of PWT, the technology is only now reaching a level of development where it can be commercially used. This study determined the main obstacles hindering the implementation of PWT and developed design principles for overcoming the process limitations through control of the plasma-liquid interphase dynamics. We have determined the efficacy of the plasma process for treatment of a wide range of different compounds and used the results of this investigation to construct a model to predict the approximate treatability of any compound based on just a few of the compound’s physical properties.
One practical outcome of these findings is a bench-scale process based on electrical discharge plasma that is capable of treating perfluoroalkyl substances (PFASs) in groundwater from a naval site with high enough efficiency to rival leading treatment technologies. Following extensive experiments with the bench-scale plasma reactor, a scaled-up continuous-flow prototype unit was constructed wherein the PFASs degradation rates far exceed those attainable in the bench scale version of the reactor. While the pilot scale plasma reactor system will soon be demonstrated for the treatment of PFAS-contaminated groundwater at an Air Force Base, another practical solution to using plasma to degrade high flowrates of PFAS-containing water is to combine it with an ion exchange (IX) treatment system wherein the plasma is used to treat IX regeneration brine. To treat brine, we have adapted the plasma reactor originally developed for low concentration, low conductivity PFAS-contaminated water and in the reactor adaptation process had to overcome treatment challenges associated with two physicochemical properties of brine solutions.