State of the art and perspectives about non-thermal plasma applications for the removal of PFAS in water

The urgent need to remove emerging contaminates from wastewater before their discharge in the environment imposes - not only from an environmental point of view, but also soon from a cogent legislative one - the development and adoption of innovative tertiary treatments. The technologies present on the market to the present day still do not reach the ideal features desirable for such processes especially for the removal of highly recalcitrant compounds such as the Perfluorinated Alkyl Substances (PFAS) which are poorly abated using “traditional” Advanced Oxidation Processes (AOPs). The non-thermal plasma (NTP) treatment is a promising technology based on the production (in the water or immediately above the liquid) of a NTP capable of producing reactive species both in the liquid and gaseous phase. These species can react with stable and recalcitrant compounds (e.g. PFAS) up to their mineralization. In this review, the NTP technology and its applications in wastewater treatment are reviewed, starting from the physics of the plasma, the different processes and reactors proposed in the literature, and the nature of the reactive species generated during the plasma process. Attention is dedicated to the applications of NTP for the abatement of Contaminants of Emerging Concern (CECs), with a focus on PFAS removal. Furthermore, the effects of the natural components of the waters, such as Natural Organic Matter (NOM), pH, and conductivity on the efficiency of NTP-based treatment are discussed. Lastly, based on an overall vision of the published literature on this topic and of the technologies available on the market to the present day, some conclusions regarding the future of this technology have been drawn.