Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic chemicals that are highly resistant to degradation because of the strong C-F bond and their unique physico-chemical properties. Several techniques, both destructive and non-destructive, have been explored for removing PFAS from contaminated water. However, the most desirable techniques, ideally capable of effective separation and complete PFAS destruction and mineralization, have not progressed beyond bench-scale testing. This paper provides an overview of the existing treatment techniques demonstrated at laboratory, pilot, and industrial scales, and their associated treatment mechanisms. Insufficient data on pilot-scale and full-scale applications for PFAS remediation has limited the optimization and advancement of these systems at a large scale. Most research related to PFAS-remediation is based on laboratory-scale studies under ideal conditions that do not represent the complexity of PFAS-contaminated media. Factors such as inhibition by competing background compounds and secondary water or air pollution limit the application of some PFAS removal techniques at full-scale. Additionally, high energy intensity, cost, and inappropriate reactor design restrict the scalability of some proposed innovations. Here, we propose integrated systems and treatment trains as potential approaches to effectively remove and destroy PFAS from contaminated waters. This review also offers and contextualizes implementation barriers and scalable approaches for PFAS treatment.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are persistent compounds characterized by stable C−F bonds giving them high thermal and chemical stability. Numerous studies have highlighted the presence of PFASs in the environment, surface waters and animals and humans. Exposure to these chemicals has been found to cause various health effects and has necessitated the need to develop methods to remove them from the environment. To date, the use of photocatalytic degradation and membrane separation to remove PFASs from water has been widely studied; however, these methods have drawbacks hindering them from being applied at full scale, including the recovery of the photocatalyst, uneven light distribution and membrane fouling. Therefore, to overcome some of these challenges, there has been research involving the coupling of photocatalysis and membrane separation to form photocatalytic membrane reactors which facilitate in the recovery of the photocatalyst, ensuring even light distribution and mitigating fouling. This review not only highlights recent advancements in the removal of PFASs using photocatalysis and membrane separation but also provides comprehensive information on the integration of photocatalysis and membrane separation to form photocatalytic membrane reactors. It emphasizes the performance of immobilized and slurry systems in PFAS removal while also addressing the associated challenges and offering recommendations for improvement. Factors influencing the performance of these methods will be comprehensively discussed, as well as the nanomaterials used for each technology. Additionally, knowledge gaps regarding the removal of PFASs using integrated photocatalytic membrane systems will be addressed, along with a comprehensive discussion on how these technologies can be applied in real-world applications.

Laboratory experiments conducted for long time on stream (TOS: 14,350 h) provide information on Fischer–Tropsch synthesis (FTS) that is representative of time scales of industrial operations. Operation conditions that deliver desirable conversion and product distribution were investigated. Low gas hourly space velocity (GHSV) gave the highest conversion of 20.97% with the highest C₅₊ selectivity achieved was 59.77%, which was obtained at the highest GHSV level. A one-way ANOVA, followed by a post-hoc Bonferroni correction test, indicated a significant difference in response to GHSV with P(T <=t) two-tail values ranging from 1.5 × 10⁻⁴ to 2.7 × 10⁻³⁵. The optimum condition for paraffin production is high pressure and low GHSV: in our experiments, this corresponded to 20.85 bar (abs): 648 h⁻¹. Conversely, olefins production is favored low pressure and low GHSV [1.85 bar (abs): 648 h⁻¹]. C₅₊ production was favored at high GHSV (2592 h⁻¹) and was very sensitive to GHSV, as the sensitivity to C₅₊ products dropped sharply when the GHSV decreased to low values (from 1296 to 648 h⁻¹); furthermore, the selectivity to C₅₊ was found to be independent of pressure. The pressure effect on selectivity is complex and selectivity toward overall gaseous (paraffin + olefin) hydrocarbons and C₅₊ does not seem to be significantly affected by variations in pressure. Long TOS FTS runs are possible ca. 14,500 h though product distribution trends tend to be changed. The catalyst survived long runs, though the selectivity to FTS became comparatively less favored than WGS with increasing TOS. Our findings may have useful implication for the design of a mobile small-scale biomass/waste to liquid process that would last for period similar to that of an industrial plant.