Comparative performance assessment of plasma reactors for the treatment of PFOA; reactor design, kinetics, mineralization and energy yield

Abstract

The development of efficient plasma-based technologies for water treatment in general and decontamination from perfluoroalkyl substances, in particular, is a timely and challenging research topic. This study investigated the degradation of PFOA (perfluorooctanoic acid) in water using three reactors with different configurations and implementing different plasma regimes. Two reactors were available from previous studies on other recalcitrant pollutants and use, respectively, corona discharge and plasma in gas bubbles. The third reactor was designed and developed for this specific application and uses a self-pulsing streamer discharge (SPD) over the liquid surface. The performance of the three reactors was assessed and compared using air as plasma feed gas and a PFOA solution (41.4 mg/L) in Milli-Q-water. The SPD reactor was found to be the most efficient in terms of energy efficiency and PFOA conversion and degradation rate. It was therefore further tested and characterized by studying the effects of changing the aqueous media in which PFOA was dissolved (Milli-Q and tap water) and the plasma feed gas (synthetic air, ambient air and argon). Due to the formation of nitrous and nitric acids, especially for plasma generated in ambient and synthetic air, the solution pH, conductivity, and hence the plasma input power changed significantly during the experiments. The best results were obtained using argon for plasma inception and PFOA solutions in tap water: the energy efficiency and fluoride recovery were 561 mg/kWh and 47%, respectively.