As a result of continued production and use, per- and polyfluoroalkyl substances (PFAS) have become widespread in the environment, including drinking water, rivers, groundwater, wastewater, household dust, and soils. Since the C-F bond is very stable, these compounds are also very stable, allowing them to be classified as persistent organic pollutants (POPs). They are used globally making them of high environmental impact worldwide. PFAS enter the environment from manufacturing processes, waste discharge, waste/chemical spills, use and disposal of consumer products, firefighter training exercises, and fire suppression events using foam sprays (Shahsavari et al., 2021). Drinking water sources including rivers, lakes, and groundwater may also be contaminated with PFAS originating from industrial sources. There may also be a significant exposure risk from PFAS-contaminated sewage sludge (biosolids) and recycled water from wastewater treatment plants, which are often used in agriculture, with exposure through contaminated soils and crop foods. PFAS are persistent and bio-accumulative and have been detected in humans, wildlife, and the environment; and can even be found in isolated regions of the world, such as the Arctic. PFOA is one of the predominant perfluorinated compounds (PFCs). PFOA has been used in a variety of products, such as a surfactant in many manufactured products in coating additives, cleaning products, and fire-fighting foam. USEPA also has recommended that PFOA be labeled as a probable human carcinogen. People can be exposed to PFOA by drinking contaminated water, eating fish caught from contaminated water bodies, swallowing contaminated soil or dust, eating food that was packaged in material that contains PFOA, and using consumer products such as non-stick cookware, stain-resistant carpeting, and water-repellant clothing (Villaroman and Custance, 2005). Research has shown that the majority of exposure to PFOA comes from food. Drinking water can be a major source of PFOA if levels are high. In 2016, the EPA published a lifetime Health Advisory of 70 ng/L for PFOA in drinking water. The EPA evaluated several studies including those that observed effects on immune response, development, and liver and kidney toxicity (Waters, 2020).
Per-and poly-fluoroalkyl substances (PFAS) are a group of synthetic man-made compounds manufactured for their ability to interact between two immiscible fluid phases acting as a surfactant (Buck et al., 2011; Rahman et al., 2014). PFAS are highly polar and contain strong carbon-fluorine bonds (CF) which display unique amphiphilic properties. Generally, most PFAS exhibit (i) high thermal resistance, (ii) high chemical stability, and (iii) resistance to biotic degradation. Two major classifications of these compounds are based on the involvement of fluorine in the compounds in deciding the final application. Perfluoroalkyl substancestypically comprises short and long carbons chains (C2-C13) and have a charged functional group head that is attached to one end. Generally, this functional group will be carboxylic or sulfonic acid.
Polyfluoroalkyl substances are not fully fluorinated. These substances have at least one lapse in the chain which is not a fluorinated atom—typically hydrogen or oxygen—which attaches to one of the carbon-chain tails. Polyfluoroalkyl chains contain carbon-hydrogen (C-H) bonds which create weak chains that are susceptible to biotic or abiotic degradation. Three specific PFAS compounds are perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and perfluorohexane sulfonate (PFHxS). Within environmental pH values, both PFOA and PFOS exist as anions (Rahman et al., 2014). Generally, it does not degrade in water or soil under normal conditions, although it is thought that it can undergo physiochemical changes and break down into smaller alkyl chains.
Studies on workers and people living in areas with high levels of PFOA show that PFOA may increase cholesterol, damage the liver, cause pregnancy-induced hypertension, increase the risk for thyroid disease, decrease antibody response to vaccines, decrease fertility, and cause small decreases in birth weight. Studies in research animals have found that PFOA can cause damage to the liver and the immune system, birth defects, delayed development, and newborn deaths in lab animals. The International Agency for Research on Cancer (IARC) classifies PFOA as possibly carcinogenic to humans and the EPA states there is suggestive evidence of carcinogenic potential for PFOA. PFOA has been shown to be genotoxic in some tests but has not been shown to be mutagenic. Both PFOA and PFOS have been shown to cause the same or similar effects on the immune system, development, and reproduction in people and research animals indicating that PFOA can cause interactive effects. Department of Health Services (DHS) recommends a combined enforcement standard of 20 nanograms per liter (ng/L) including both PFOS and PFOA in groundwater.
Some of the major effects observed in humans after the exposure to PFOA contaminated water beyond the safe limit of drinking.
There are various technologies available for the removal of organic contaminants in water. Few technologies provided the complete mineralization of organic compounds but some have the focus only on the physical removal. So, the various technologies have been tested for the removal of PFOA compounds but not a single technology could provide a complete solution on the basis of efficiency, economic feasibility, and sustainability.
|Adsorption||Selective materials for adsorption like biochar, activated carbon, modified clays||Ex-situ/ In-situ||Low operational cost, an abundance of materials||Ineffective for short-chain compounds interfere with other pollutants due to reduced surface area|
|Filtration||Reverse osmosis, ultra-filtration, nano-filtration||Ex-situ||Effective under a wide pH range||Expensive, more contaminated rejection stream|
|Thermal||Contaminants vaporization at 600 to 1000 C||Ex-situ||High destruction of organic compounds||Time intensive, cost-intensive, energy-intensive|
|Chemical redox potential||Chemical oxidants/reductants for an abiotic breakdown of contaminants||In-situ/ Ex-situ||PFOA mineralization, effective PFAS removal||Expensive, huge quantity, interfere with other contaminants|
|Bio-remediation||Biological agents like microbes, bacteria, and plants||In-situ/ Ex-situ||Simple, cost-effective, green approach||Long time, slow degradation|
A couple of technologies may be an effective solution for PFOA mineralization. The solution to the problem of PFAS compounds contamination, a filter cartridge was designed filled with efficient inorganic and organic adsorbents. The inorganic adsorbent was developed by the mild chemical treatment (Acid-base hydrolysis) of the cheaper raw materials. These raw materials are abundantly available in the environment as the rich source of iron, aluminum, and manganese. Various phases have been developed in the adsorbent with the additional redox functionality after the chemical treatment. The redox potential of the inorganic adsorbent could enhance the removal activity for heavy metals and some redox-active organic compounds. Later, the organic adsorbent was derived from the organic biomass (plant leaves, stem, roots, etc.) freely and abundantly available in the environment. This biomass was processed under a high temperature in the absence of air to produce biochar. Before the pyrolysis, the biomass was modified with the raw inorganic fillers used in the inorganic adsorbent preparation. It may result in a more stable organic-inorganic adsorbent for the desired water treatment application (Xu et al., 2020). Finally, after multiple washing and drying, both inorganic, organic, and organic-inorganic adsorbents were prepared as the filtration cartridge’s feedstock.
Our solution provides the flexibility of using the cartridge as an in-house water purification filter system. The cartridge with prepared adsorbent can be fitted easily with the existing water purification system. The cartridge efficiency was estimated so that the 1-1.5 kg adsorbent could produce nearly 8000-10000 L of water. However, this amount could cater to the need for the drinking water for the nuclear family of 4 members to last for 1 year. The system is also employed to fulfill the requirement of the community by designing a commercial water filtration unit with a vast capacity for treating water. Also, the groundwater quality is crucial for developing the exact filter cartridge for the specific application. Here the assistance of the UV cartridge enhances the performance of the water filter system in case of organic compounds like PFOA removal (Cheng et al., 2014). It can disintegrate the C-F bond of the PFOA and leave the lower chain fluorinated compounds (Cheng et al., 2014). These compounds have comparatively less hazardous impacts concerning PFOA. During dissociation, elemental fluorine comes out from the compounds, which the inorganic adsorbent could efficiently adsorb. Inorganic exhausted adsorbent could be disposed of by mixing it with the mortar for the plaster or brick masonry work. The exhausted organic adsorbent was sent to a landfill with no contaminant leaching but assists in soil’s nutrient accumulation. Alternatively, the organic adsorbent containing organic contaminant was sent to an incinerator for regeneration. The solution can also be projected for the municipal application by designing a complete filtration unit with a large capacity of filters.
It has been recommended to avoid using the products containing such compounds to increase the healthy life span. Secondly, consume the safe and pure drinking water or food after proper treatment. The half-life period of such compounds are nearly 3-4 years, but once they are degraded into small chains their half-life falls into days like 30-40 days. So, the proposed solution has the ability to dissociate these long chain polymer into small chains with respective release of elemental fluorine with the help of UV radiation (< 220 nm). Our technology will provide the total elimination of short or long chain compounds with an added removal of total fluorine along with other heavy metal ions. Thus, the solution can be implemented in any place in the World, depending on the PFOA contamination.
Therefore, regulatory bodies are continuously monitoring the quality parameters of the groundwater, surface water, and industrial effluents to eliminate the risk of such contamination in water. A documentary has been published detailing the risk and hazards caused by the PFAS compounds on humans. There are some market players with their solutions for the removal of these compounds, but somehow dangling in achieving the right solution. Specifically, the companies are using granular activated carbon bed filters for adsorption, nano-filtration also to physically separate the compounds, and ion exchange works similar to the separation. Also, the biological solution is under the development stage, it does not clear the exact solution is right now.
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Cheng, J., Liang, X., Yang, S., Hu, Y., 2014. Photochemical defluorination of aqueous perfluorooctanoic acid (PFOA) by VUV/Fe3+ system. Chem. Eng. J. 239, 242–249. https://doi.org/10.1016/j.cej.2013.11.023
Rahman, M.F., Peldszus, S., Anderson, W.B., 2014. Behaviour and fate of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water treatment: A review. Water Res. 50, 318–340. https://doi.org/10.1016/j.watres.2013.10.045
Shahsavari, E., Rouch, D., Khudur, L.S., Thomas, D., Aburto-Medina, A., Ball, A.S., 2021. Challenges and Current Status of the Biological Treatment of PFAS-Contaminated Soils. Front. Bioeng. Biotechnol. 8, 1–15. https://doi.org/10.3389/fbioe.2020.602040
Villaroman, C., Custance, R., 2005. Perfluorooctanoic Acid (PFOA), in: Encyclopedia of Toxicology. Elsevier, pp. 355–358. https://doi.org/10.1016/B0-12-369400-0/01059-0
Waters, 2020. [ STARTUP GUIDE ] Startup Guide for the Analysis of Perfluorinated Alkyl Substances ( PFAS ) in Environmental Samples CONTAMINATION SOURCES [ STARTUP GUIDE ].
Xu, T., Ji, H., Gu, Y., Tong, T., Xia, Y., Zhang, L., Zhao, D., 2020. Enhanced adsorption and photocatalytic degradation of perfluorooctanoic acid in water using iron (hydr)oxides/carbon sphere composite. Chem. Eng. J. 388, 124230. https://doi.org/10.1016/j.cej.2020.124230