Toxic Effect and Treatment Process of Per- and Polyfluoroalkyl Substances (PFASs) Presence in Industrial Waste Water

Abstract

The presence of Per- and Polyfluoroalkyl Substances (PFASs) in water has raised concerns due to its potential adverse human health effects. These chemicals are toxic in nature and very stable which are not biodegradable. Researchers are studying the fate and transport phenomenon of these chemicals and developing techniques to removes them from contaminated water. Most of the existing water treatment technologies are not effective in removing them. Nanotechnology-based water treatment processes are creating interest because they show significant improvement in capturing PFASs and their replacement chemicals, such as GenX. This paper reviewed the potential human health effects of PFASs, also the current trend of water treatment technologies which are applied to remove/adsorb them from the water.

Keywords: Per- and Polyfluoroalkyl Substances, waster water, toxic chemical, water treatment

Introduction

 According to USEPA, “Per- and Polyfluoroalkyl substances (PFASs) are a group of manufactured substances that includes Perfluorooctanoic acid (PFOA), Perfluorooctane Sulfonate (PFOS), GenX, and many other chemicals”. Since the 1940s, these substances have been manufactured and commercialized to use in the various industry around the world, including the United States [1]. The most common and widely used chemicals of this type are Perfluorooctanoic acid (PFOA) and Perfluorooctane Sulfonate (PFOS) which are very rigid and do not degrade in the environment. They can accrue in the human body and causes significant health effects.

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 PFASs are widely found in various consumer products including food packages, commercial household products such as stain- and water-repellent fabrics, nonstick products (e.g., Teflon), polishes, waxes, paints, cleaning products, and fire-fighting foams (a major source of groundwater contamination at airports and military bases where firefighting training occurs) for their water and oil-repelling abilities [2].  They also found in workplaces, including production facilities or industries (e.g., chrome plating, electronics manufacturing or oil recovery) that use PFAS. Moreover, drinking water get contaminant with PFASs typically localized and associated with a specific facility (e.g., manufacturer, landfill, wastewater treatment plant, firefighter training facility). Which in-turns, causes living organisms including fish, animals, and humans to be contaminated by PFAS and PFAS have the ability to build up and persist over time.

 The need for removal of PFASs from wastewater is growing as the toxic effect of PFAS causes serious effect on human health. Traditional water purification technologies are mostly ineffective in removing PFASs and their replacement chemical such as GenX from the water. Conventional water treatment process such as coagulation/physical separation, oxidation, aeration, disinfection, are not able to remove any PFAS. Nanomaterials and nanotechnology-based water treatment processes show the significant removal of PFAS from the water. Granular activated carbon, powder activated carbon, nanofiltration, show effectiveness in removal of PFASs from water in some extent but they do not selectively remove PFASs. Ji et al., (2018) created an amine-functionalized covalent organic framework

Chemical Structure of the Selected Elements

 PFOA and PFOS are made up of “chains” of eight carbon atoms that are attached to fluorine and other atoms. Replacement chemicals, like GenX, tend to have fewer carbon atoms in the chain but have many similar physical and chemical properties as their predecessors (e.g. they both repel oil and water) [1]. In PFASs structures, all hydrogen atoms of the corresponding hydrocarbon compound are substituted for fluorine atoms. The polar carbon-fluorine bond is the most stable bond in organic chemistry. Therefore, PFASs are thermally and chemically more stable than the analogue hydrocarbons. Generally, they consist of a hydrophilic end group, i.e. sulfonate or carboxylate end group, and a hydrophobic perfluorinated carbon chain (Figure 1) [3].

Figure 1: Structural formula of perfluoroalkycarboxylates and sulfonates; in technical products also, molecules with shorter and longer perfluoroalkyl chain may occur to some extent

 GenX is the commercial name of perfluoro-2-propoxypropanoic acid (CAS No. 62037- 80-3). The chemical structure of GenX is shown in Figure 2. GenX is a type of per-and polyfluoroalkyl substances (PFAS), which are used in products ranging from food packagings such as popcorn bags and pizza boxes to household products like Teflon and electronic components [1].

Figure 2: GenX

Figure 3 shows the common anion of GenX when it dissolved in water it leaves the ammonium groups [4]. Table 1 represented the detail information (nomenclature and properties) about GenX.

Figure 3: GenX carboxylate anion that forms in water

Table 1 GenX nomenclature and properties

Toxic Effects

 There are lot of studies showing PFASs and GenX are toxic to a living organism such as human and it is very likely that people can be exposed to these toxic chemicals in various ways. If humans, or animals, ingest PFAS (by eating or drinking food or water that contain PFASs), the PFASs are absorbed and can accumulate in the body. PFASs stay in the human body for long periods of time. As a result, as people get exposed to PFAS from different sources over time, the level of PFAS in their bodies may increase to the point where they suffer from adverse health effects. Studies indicate that PFOA and PFOS can cause reproductive and developmental, liver and kidney, and immunological effects in laboratory animals. Both chemicals have caused tumors in animal studies. Studies found that exposure to PFASs can cause to the following health issues [1, 5]:

affect growth, learning, and behavior of infants and older children

lower a woman’s chance of getting pregnant

interfere with the body’s natural hormones

increase cholesterol levels

affect the immune system

increase the risk of cancer

low infant birth weights,

effects on the immune system,

cancer (for PFOA), and

thyroid hormone disruption (for PFOS).

Treatment Process of PFASs

 Since PFASs are not biodegradable, researcher applied common water treatment process to see how much they can remove. Common water treatment process including, Coagulation, Oxidation, Aeration, Disinfection, Riverbank filtration, Anion exchange, Reverse osmosis, Granulated activated carbon treatment, Nanofiltration, Ozofractionation, Electrochemical oxidation, Sonolysis, etc. Most of the conventional water treatment processes are failed to remove PFASs from the water. Recent nanotechnology-based selective removal of PFASs showed significant effectiveness in removing of these toxic chemicals from water.

Coagulation

Appleman et al., (2014) studied the full-scale water treatment systems for the removal of PFASs where they justified various techniques including coagulation if they were able to remove PFASs from the water. They applied coagulation followed by sedimentation or Dissolved Air Flotation (DAF) and/or filtration to treat the wastewater. The used coagulants included aluminum sulfate and polymer in one sample and aluminum sulfate in the second sample, and polyaluminum chloride in the third sample. The results found that, Coagulation followed by sedimentation did not lead to PFAS removal, but where DAF was used instead of sedimentation, a 49% removal of PFAS was observed. Figure 4 represents the typical coagulation method for water treatment.

Figure 4: Coagulation method to remove impurities from water.

Oxidation

 Oxidation and disinfection processes including ozonation, aeration packed towers, potassium permanganate, ultraviolet (UV) treatment, chlorination (Cl2) with and without chloramination, and chlorine dioxide, all of these processes proved mostly ineffective in removing of PFAS (Appleman et al., 2014). Typical oxidation and disinfection process is shown in figure 5.

Figure 5: Oxidation and disinfection method

Anion Exchange

 Iron infused anion exchange resin was designed for arsenic removal and it was further used for PFASs removal by Appleman et al., (2014). The resin was successful in reducing some of the PFAS levels. In particular, PFHpA was partially removed (46%), as were PFOA (75%), and PFBS (81%). PFNA, which was only detected in one of the two raw water samples, exhibited >67% removal. It is possible that certain AIX resins can target PFAS sorption by ion exchange and/or hydrophobic interactions. Detail Anion exchange method is given in figure 6.

Figure 6: Anion exchange method for water treatment

Reverse Osmosis (RO)

 Figure 7 depicts the water treatment technology for reverse osmosis which can be used for removal of PFASs from the water.

Figure 7: Reverse osmosis principle

Appleman et al., (2014) in their full-scale water treatment for PFASs removal, among other existing practice they used reverse osmosis technique to remove PFASs. They applied polyamide Hydranautics ESPA2 membranes in a three-stage array with a 12 gfd flux rate and 85% recovery in one site, and used Toray and Hydranautics RO membranes with an RO flux rate of 12 gfd and 80% recovery for another site. Results found that RO was most effective in removing PFASs from water compared to all other techniques they used.

Granulated Activated Carbon (GAC)

Granulated activated carbon was used to remove PFASs from water in different water facilities by Appleman et al., (2014). They utilized Calgon F600 (coal-based) media and was set up with two contactors, a lead and a lag, that run-in series with a flow between 1.4 and 1.5 m3/min, and an empty bed contact time (EBCT) of approximately 13 min in each contactor. Results found that GAC treatment was effective in removing PFASs from the water.

Amine-Functionalized Covalent Organic Frameworks

 Recently Ji et al., (2018) created aa amine functionalized covalent organic frameworks for next-generation water treatment of PFASs removal [6]. The idea of this system was to remove PFASs and GenX from water by selective adsorption. The cost and performance limitations of current PFAS removal technologies motivate authors to develop selective and high-affinity adsorbents. Covalent organic frameworks (COFs) are unexplored yet promising adsorbents because of their high surface area and tunable pore sizes. Authors reduced the azide-functionalized COFs to the corresponding amine functionalized networks and demonstrate their promise as adsorbents for PFAS. The COFs amine groups interact with the anionic head group of PFAS, along with ample hydrophobic surface area that further support adsorption. The optimized materials, with amine loadings of 20–28%, bind 13 PFAS with high affinity and rapid kinetics. Figure 8 depicts the amine functionalized covalent organic frameworks.

Figure 8: Amine functionalized covalent organic frameworks for PFASs adsorption

Results & Discussion

 Table 2 represents the results of currently available water treatment mostly they are not able to remove PFASs from water effectively [7]. Some technique may be able to remove PFASs but they have other challenges too such as maintaining cost, operation cost and other.

Table 2 Results of different type of water treatment processes

While all other techniques are not effective in reducing PFASs from water, amine functionalized covalent organic frameworks shows significant improvement and selective removal of PFASs and GenX from the water. Figure 9 depicts the removal efficiency of PFASs by amine functionalized covalent organic frameworks where it shows 12 out of 13 PFASs removes effectively. Figure 10 shows, GenX removal efficiency.

Figure 9: PFASs removal efficiency

Figure 10: GenX removal efficiency

Later, in Figure 11 the GenX removal efficiency by amine functionalized covalent organic frameworks was compared with Granular activated carbon, and powder activated carbon; nevertheless, the amine functionalized covalent organic frameworks shows the highest efficiency.

Figure 11: GenX removal efficiency comparison among different approaches

Conclusion

 In conclusion, this project reviewed the toxic effects of PFASs and other replacement chemicals of PAFSs such as GenX and their available removal technology. Most of the conventional water treatment processes such as coagulation followed by physical separation processes, and chemical oxidation, aeration, and disinfection, were unable to remove PFASs. Some techniques, such as granular activated carbon, anion exchange, and reverse osmosis show effectiveness to some extent. Amine functionalized covalent organic frameworks showed significant removal efficiency where this technique removes impurities selectively.

References

[1] https://www.epa.gov/pfas/basic-information-pfas (accessed on 11-18-2018).

[2]. Lau, C., Anitole, K., Hodes, C., Lai, D., Pfahles-Hutchens, A., & Seed, J. (2007). Perfluoroalkyl acids: a review of monitoring and toxicological findings. Toxicological sciences, 99(2), 366-394.

[3]. https://www.riwa-rijn.org/wp-content/uploads/2015/05/137_ptfe_report.pdf (accessed on 11-18-2018).

[4]. Hopkins, Z. R., Sun, M., DeWitt, J. C., & Knappe, D. R. (2018). Recently Detected Drinking Water Contaminants: GenX and Other Per‐and Polyfluoroalkyl Ether Acids. Journal‐American Water Works Association.

[5]. https://www.atsdr.cdc.gov/pfas/health-effects.html (accessed on 11-19-2018).

[6]. Ji, W., Xiao, L., Ling, Y., Ching, C., Matsumoto, M., Bisbey, R. P., … & Dichtel, W. R. (2018). Removal of GenX and Perfluorinated Alkyl Substances from Water by Amine-Functionalized Covalent Organic Frameworks. Journal of the American Chemical Society, 140(40), 12677-12681.

[7]. Hopkins, Z. R., Sun, M., DeWitt, J. C., & Knappe, D. R. (2018). Recently Detected Drinking Water Contaminants: GenX and Other Per‐and Polyfluoroalkyl Ether Acids. Journal‐American Water Works Association.