# Light-Induced Advanced Oxidation Processes as PFAS Remediation Methods: A Review
## 2 PFAS Applications and Related Concerns
### Physical Separation vs. Advanced Oxidation Processes  
Physical separation methods remain the most common treatments for PFAS-contaminated liquids. Although such methods do not degrade PFAS, these processes are considered as a rapid solution involving only the mass transfer of PFAS from one media to another. These approaches can process extremely large volumes of liquid possessing low PFAS concentrations (levels of ppt to ppb), with the drawback of demanding consequent disposal, generally by incineration in furnaces [26].  
Among physical separation technologies, the most employed techniques are procedures such as sorption on granulars of different particles, nanotubes of activated carbon (AC), biomaterials, molecularly imprinted polymers (resins), and mineral composites (e.g., zeolites). As mentioned, all these processes require further, generally off-site, treatment steps [27].  
In the case of AC, the main issues are related to the poor removal of short-chained PFAS, difficulties in disposal, and eventually in the reactivation of carbon and the corresponding need for regeneration. These steps are necessary due to the reduction in removal efficiency with use. If frequent replacement of the material is ensured, AC can achieve 10-97% removal of PFAS [28].  
The application of ion exchange resins provides up to 90-99% efficiency for some PFASs, although poor removal for selected PFAS is an unsolved problem, along with the potential complications related to the incineration and disposal of the adsorbents [29].  
High-pressure filtration membranes are generally related to elevated capital and operation costs, uncertain corrosion control, lack of options for concentrate stream treatment or disposal, and finally membrane fouling. Furthermore, in this case, despite several disadvantages such as those mentioned above, the reported levels of PFAS removal from water range between 93% and 99% [30].  
Emerging treatment methods are based on a series of chemical reactions which eventually result in PFAS degradation directly in water streams. Among these techniques, electrochemical oxidation, photocatalysis, photolysis, reduction processes using for example customized iodide or dithionite and sulfites, high-voltage electric discharges, bioremediation using microbial and fungal treatment, sonochemical degradation, ozonation under alkaline conditions, permanganate oxidation, sub or supercritical treatment, and microwave-hydrothermal treatments have been applied to PFAS degradation, with varying degrees of effectiveness [31]. Electrochemical oxidation, plasma, sonolysis, and hydrothermal/supercritical oxidation are some emerging technologies that are in the process of transitioning from laboratory-scale research to field-scale testing [32]. While promising, these technologies need extreme operating conditions, centralized laboratory equipment, and/or high chemical and energy requirements [30].  
A combination of different approaches (perhaps using in situ and ex situ approaches) may be needed at a given site to cost-effectively address other areas with different water settings, orders of magnitude in concentration, co-contaminants, and remedial objectives. Selecting the most appropriate remedial strategy for PFAS is challenging. In this review paper we indicate the most promising technologies.