### Membrane Processes  
[PERSON] et al. [31] conducted a review on PFAS remediation using membrane processes. Membranes were categorized into two groups: size-dependent and pressure-sensitive membranes. Low-pressure membranes, such as MF (100-400 nm) and UF (-10 nm), were capable of separating high-molecular-weight (MW) PFASs (e.g., PFNA, PFOS, and PFOA) but exhibited low efficiency in separating low MW PFAS (e.g., PFBS or PFHxS) from water. The literature values for PFOA and PFOS removal by low-pressure membranes ranged from 0 to 23 percent [25]. In the evaluation by [PERSON] et al. [27] of two full-scale treatment systems in the US for PFAS attenuation, it was found that MF and UF were mostly ineffective, resulting in only partial reductions in the concentrations of PFASs. Specifically, reductions of 24% for PFOS, 44% for PFDoA, and 42% for FOSA were observed. In their study, [PERSON] et al. [32] employed a commercially available UF membrane (UA60, Trisep), with a pore size distribution in the range of 1000 Daltons. They also investigated the effects of modification by functionalizing the membrane with polyacrylic acid and polyallylamine hydrochloride for the removal of PFOS and PFOA. The results indicated that the unmodified UF membrane achieved only 21.8 \(\pm\) 11.6% and 20.6 \(\pm\) 6.9% removals of PFOS and PFOA, respectively. In contrast, the modified UF membrane exhibited improved removal, achieving 52.1 \(\pm\) 10.2% and 50.4 \(\pm\) 9.5% removals for PFOS and PFOA, respectively. This represents an increase of 30% in removal efficiency. The enhanced removal was attributed to an approximately 38% reduction in membrane MWCO (molecular weight cut-off) and a 9.2% reduction in membrane porosity due to the modifications. However, it is noteworthy that the removal efficiencies obtained by both the unmodified and modified UF membranes were not as high as those reported in other studies using NF and RO processes. In contrast to low-pressure membranes, high-pressure membranes, such as NF and RO, have proven to be highly effective in separating both low-MW and high-MW PFASs from wastewater [31]. NF and RO processes have been found to efficiently remove various PFAS, including PFAA precursors, with size exclusion suggested as the primary mechanism in this filtration process. Additionally, other mechanisms like electrostatic repulsion, diffusion, and cake layer filtration may also play a role during the process. When comparing NF and RO, NF (especially the NF270) is recommended as a better option for PFAS removal due to its lower cost [25]. [PERSON] et al. [33] reported high PFOA removal efficienciesusing NF filtration (fully aromatic polyamide advanced composite membrane, membrane model 2540-ACMS-TSF, 2.5\({}^{\prime\prime}\) diameter) with 99.78-99.87% removal efficiency for spiked deionized water and 99.49-99.54% for spiked groundwater samples. [PERSON] et al. [25] conducted a comprehensive literature review and reported that RO is highly effective in removing PFASs (>99%) regardless of chain length, utilizing size exclusion and charge rejection mechanisms. However, the operation cost of RO is high due to the requirement for high pressure [27]. On the other hand, NF membranes with larger pores operate at lower pressures and employ mechanisms like electrostatic repulsion, hydrophobicity, and dipole moments to remove short-chain PFAS, which are too small to be solely rejected by size exclusion [23; 28]. Despite the effectiveness of high-pressure membranes for PFAS removal, there are some limitations highlighted by [PERSON] et al. [25] in their review. High recovery rates (typically around 80 percent for non-desalination systems) lead to the production of a concentrated retentate stream (20 percent of feed volume), which requires treatment before disposal. Dealing with this retentate stream poses significant challenges and costs due to its higher concentrations and volume. To optimize the cost efficiency of the membrane treatment, the residual stream treatment scheme should be carefully designed.