A Review on Removal and Destruction of Per- and Polyfluoroalkyl Substances (PFAS) by Novel Membranes

Abstract

Per- and Polyfluoroalkyl Substances (PFAS) are anthropogenic chemicals consisting of thousands of individual species. PFAS consists of a fully or partly fluorinated carbon-fluorine bond, which is hard to break and requires a high amount of energy (536 kJ/mole). Resulting from their unique hydrophobic/oleophobic nature and their chemical and mechanical stability, they are highly resistant to thermal, chemical, and biological degradation. PFAS have been used extensively worldwide since the 1940s in various products such as non-stick household items, food-packaging, cosmetics, electronics, and firefighting foams. Exposure to PFAS may lead to health issues such as hormonal imbalances, a compromised immune system, cancer, fertility disorders, and adverse effects on fetal growth and learning ability in children. To date, very few novel membrane approaches have been reported effective in removing and destroying PFAS. Therefore, this article provides a critical review of PFAS treatment and removal approaches by membrane separation systems. We discuss recently reported novel and effective membrane techniques for PFAS separation and include a detailed discussion of parameters affecting PFAS membrane separation and destruction. Moreover, an estimation of cost analysis is also included for each treatment technology. Additionally, since the PFAS treatment technology is still growing, we have incorporated several future directions for efficient PFAS treatment.

Keywords: PFAS; coupled technology; hybrid membranes; nanofiltration; novel membranes; reverse osmosis.

Figure 1

Techniques for removing Per- and Polyfluoroalkyl Substances (PFAS) from wastewater.

Figure 2

Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) images of PTFE membrane in Membrane Distillation (MD) of PFPeA (a) before filtration, (b) after filtration of 6 h at 50 °C, (c) 60 °C and (d) 70 °C feed temperatures, and (e) 60 °C feed temperatures with 72 h duration of distillation process; the permeate temperature was maintained at 20 °C for all the experiments (reprinted with permission from Ref. [24]. Copyright 2020 Elsevier).

Figure 3

Mechanism of membrane distillation process for PFAS (PFPeA) removal: (a) nucleation of surface deposition, (b) PFAS adsorption and aggregation across the membrane pores, (c) surface diffusion within the membrane pores, and (d) PFPeA coating within the pores (reprinted with permission from Ref. [24]. Copyright 2020 Elsevier).

Figure 4

PFAS binding in the modified surface.

Figure 5

Polyamide barrier layer on membrane surface with (a) PFOA adsorption and (b) charge-shielding by carboxyl groups preventing PFAS transport to the membrane surface.

Figure 6

Schematic diagram of water permeance and retention changes for Graphene Oxide (GO) and GO-PEI membranes. (a) GO layer on top of PVDF support. (b) PEI layer on top of GO layer (interlayer space reduction).

Figure 7

Metal-Organic Framework (MOF) modified PTFE membrane.

Figure 8

Pristine and used membranes after PFAS treatment (reprinted with permission from Ref. [126]. Copyright 2022 Elsevier).

Figure 9

SEM and AFM images of (a) bare thin film composite membrane (Cross-section (left) and top surface (right)), (b) 0.025 MXene−Membrane, and (c) 0.050 MXene—Membrane (reprinted with permission from Ref. [112]. Copyright 2022 ACS).

Figure 10

Schematic representation of the microwave catalyst grafted ceramic membrane for PFOA removal from wastewater.

Figure 11

SEM and AFM images of (a) pristine (with elemental analysis), (b) low BFO-coated, and (c) heavy BFO-coated (with elemental analysis); and only SEM image of (d) cross-sectional of BFO coated membranes (adapted from Ref. [134]).

Figure 12

Schematics of the filtration process of PFOA on phosphorene membranes (a) followed by either treatment using UV light or liquid aerobic oxidation (b).

Figure 13

SEM and AFM images of membrane surface: (A) plain/clean membrane, (B) the membrane after PFOA filtration, (C) the membrane after PFOA filtration and irradiation with UV, and (D) the membrane after PFOA filtration and oxygenation (adapted from Ref. [113]).