Degradation of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in water by use of a nonthermal plasma-ozonation cascade reactor: Role of different processes and reactive species

Abstract

The widespread use of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in the last century has caused serious pollution of water bodies around the world, threatening the health of humans and other organisms. In this work, a novel cascade reactor configuration, comprised of a dielectric barrier discharge (DBD) plasma chamber connected with an ozonation chamber was used to treat municipal secondary effluent loaded with several PFAS. The electrical energy per order (EE/O) for degradation of perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) amounts 180 and 100 kWh/m3, respectively. While the short-chain PFAS (perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA)) were difficult to be degraded, i.e. degradation percentage < 32 % after 60 min, 80–90 % of the longer PFAS (PFOA and PFDA) were degraded within 60 min. The degradation of PFAS mainly occurred in the plasma chamber rather than in ozonation chamber. This is because that reductive species produced in plasma chamber, such as hydrated electrons (eaq−) and Ar+, played a direct role in defluorination, while oxidative species, including OH, O, O2−, 1O2, O3, and H2O2, has a very limited contribution for defluorination. Enhancing the utilization of reductive species is crucial to degrade PFAS. Perfluoroalkyl carboxylic acids (PFCA) generated during the plasma reactions may have a potential risk for environment. As such, further optimization should focus on full mineralization. This study provides an approach to solve the problem of PFAS-contaminated wastewater, which is of the importance to promote the application of nonthermal plasma technique in water treatment.