Complete Destruction of Undiluted AFFF by a Plasma Spinning Disc Reactor
Selma Mededovic | Clarkson University
The overall objective of the project is to demonstrate the technical feasibility of using a novel plasma spinning disc reactor for the complete destruction of per- and polyfluoroalkyl substances (PFAS) in undiluted aqueous film forming foams (AFFF) and to determine the treatment costs of a scaled-up system. The general approach centers around the reactor electrode design and parametric optimization of the plasma spinning disc reactor for complete mineralization of long- and short-chain PFAS including PFAS precursors in current-use and legacy AFFFs. A special focus will be placed on determining the effects of the disc rotational speed, discharge (plasma) type and the magnitude of energy input on mineralization rates. The approach seeks to manage the challenge and complexity of AFFF by further expanding the proven plasma-based process to treat undiluted AFFF and to ultimately destroy PFAS on site.
The optimization of the plasma spinning disc reactor for treating undiluted AFFF will be a two-stage process. First, the reactor electrode design will be optimized to increase the contact of the plasma and the treated liquid. This will involve varying the diameter of the spinning disc to maximize the length of the plasma streamers (channels) and modifying the design of the high voltage plasma-generating electrode to maximize the degree of the plasma streamer branching. Next, removal rates of at least 29 PFAS, six PFAS precursors and total organic fluorine in four current-use and legacy AFFF formulations will be maximized via parametric reactor optimization. For that purpose, variations in the disc rotational speed, which directly controls the thickness of the treated liquid, will be investigated alongside the liquid flowrate across the disc and solution pH and electrical conductivity. Plasma-induced reactivity will be controlled by employing different types of plasma-generating power supplies and mineralization rates maximized by varying the magnitude of the energy input.
State-of-the-art analytical techniques will be utilized to identify and quantify byproducts of PFAS degradation in the optimized reactor and degradation pathways. The information on the starting solution composition, byproduct formation and chemical reaction pathways will assist in establishing a correlation between input process parameters and the resulting bulk liquid chemistry. This will allow the project team to design an effective spinning disc reactor system capable of completely mineralizing AFFF solutions and prepare a conceptual design for a multi-gallons per minute treatment system.
Plasma Spinning Disc Reactors
PFAS-containing AFFF foams have caused significant environmental impact with remediation efforts expected to cost in the billions of dollars. To minimize future impacts, current AFFF formulations are being replaced with shorter chain alternatives and eventually PFAS-free foams. During this switch over, significant amounts of undiluted AFFF will need to be disposed. Therefore, it is critically important to develop an effective method to mineralize undiluted AFFF that produces no waste. The further development of the electrical discharge plasma technology to treat concentrated AFFF solutions will address this need by providing the Department of Defense (DoD) with an effective and efficient technology to manage this waste and limit future liability.