Oct 4th 2019
Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) chemicals are often referred to as “forever chemicals” as they do not naturally degrade. They have contaminated some water supplies causing adverse health impacts ranging from cancer to liver disease and fertility disruption.
Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) are a group of man-made carbon-fluorine chemicals that have been produced since the 1940s. They were widely used in non-stick household products, stain-repellants, food paper packaging (e.g., compostable coffee cups and pizza boxes), lubricants, aviation firefighting foams, and many more. PFAS are comprised of a water-liking “head” group (making them soluble in water) and a long perfluoroalkyl or polyfluoroalkyl “tail” group that is made up of carbon-fluorine bonds.
The carbon-fluorine bond is one of the strongest chemical bonds, which results in PFAS chemicals not degrading easily. As such, PFAS are often called “forever chemicals”. PFAS have been found in surface water, groundwater, drinking water sources, wastewater treatment plant effluent and landfill leachates. People may be exposed to PFAS by consuming PFAS-contaminated water or food. PFAS can be harmful to human health, causing cancer, liver damage, and a depressed immune system among other impacts. The U.S. EPA is taking action by proposing regulations to protect drinking water and to clean up PFAS-contaminated water sources.
Treating PFAS contaminated water before discharge to aquatic receiving sources will reduce its accumulation in water systems. Currently, industrialized methods for removing PFAS from contaminated waters are based on (1) physical adsorption technologies, such as granular activated carbon (GAC) and ion-exchange (IX) resins; and (2) high-pressure membrane filtrations, such as nanofiltration (NF) or reverse osmosis (RO). Although work is being done on advanced oxidation techniques, these are not yet commercial and could come with a very high energy demand.
The selection of an appropriate treatment method requires careful considerations based on the specific water chemistry, contaminant removals and the required quality of the treated water. In industrial wastewater treatment, the water composition is more complex than that of “clean” drinking water and includes co-contaminants besides PFAS. The presence of co-contaminants will impact the selection of a method, the treatment system sizing and the eventual costs. For example, landfill leachate has co-contaminants of organics, inorganics and volatiles, in requiring removal in addition to PFAS and to varying degrees.
The pros and cons for the three industrialized PFAS removal methods are summarized in the below table.
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Granular activated carbon (GAC) |
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Pros
• Reduce PFAS to ng/L level for drinking water. • Effective for long-chain PFAS removal. |
Cons
• Quick PFAS (short-chain PFAS in particular) breakthrough and frequent filter replacement due to weak interactions between PFAS and carbon. • Not cost effective for waters containing other organic compounds since GAC is non-selective and will be over-loaded by other organics. • Does not remove inorganics. • GAC is a very expensive consumable. It can be manual intensive GAC to replace, or energy intensive regeneration (often off-site via extreme temperature vaporization). |
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Ion-exchange resin |
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Pros
• Effective for anionic and long-chain PFAS removal to ng/L level. • Higher adsorption capacity and significantly faster reaction kinetics compared to GAC. |
Cons
• Not effective for wastewater containing high levels of inorganic ions (i.e. TDS) and/or natural organic matter (NOM). • Less affinity for short-chain PFAS. • Incineration or regeneration of ion exchange resin required. |
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Nanofiltration or reverse osmosis |
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Pros
• Effective for both short-chain and long-chain PFAS. • Capable of handling co-contaminants and treating all types of PFAS-contaminated water. • High loading flow rate. • Can be partnered with a disposal well (common in North America) to permanently dispose of the PFAS brine. |
Cons
• Possible membrane fouling by scaling inorganic compounds. • Concentrated brine management, which can be solved through high recovery performance to minimize brine produced and disposed (concentrate the PFAS to the maximum extent in ultra-high recovery RO while avoiding scaling of RO system). |
A PFAS removal process may integrate multiple technologies, for example, an upstream reverse osmosis process with a high loading flow rate followed by a downstream GAC or IX-resin polishing step to meet stringent water quality requirements. Refer to our article for an overview of the importance of understanding the water chemistry, especially for nanofiltration and reverse osmosis processes. An experienced wastewater treatment team can engineer and price a solution including initial desk study for the PFAS-removal system, site investigations, and risk assessments.
Physical separation technologies (GAC, IX resin, NF, or RO) do not destroy PFAS but only remove PFAS from contaminated water onto adsorbents or into a concentrated brine. The disposal of PFAS-contaminated absorbents or PFAS-concentrated brine may pose secondary pollution risks. Technologies for permanently degrading PFAS are based on high-energy incineration or advanced oxidations including electrochemical oxidation, microwave thermal treatment, photolytic degradation, pyrolysis, and sonochemistry. These extreme PFAS degradation pathways are very costly, especially when treating large volumes and flow rates of PFAS wastewater. It is thus ideal to use other relatively cost-effective technologies to first reduce PFAS wastewater volume and concentrate PFAS into its highest allowable concentration together with co-contaminate removals. The highly concentrated PFAS wastewater can then be transported to either a disposal well for permanent disposal deep underground or a PFAS-specialized degradation site for final destruction.
PFAS destruction by any means will release fluorine atoms/fluoride ions. When incineration is used to destroy PFAS, fluorine may become airborne and require air scrubbing technology which may produce fluoride-rich wastewater. If using advanced oxidation instead, fluoride ions will be present in the treated water.
Saltworks is an established leader in delivering modular, automated fluoride removal plants, including to leaders in the semiconductor industry. As explained in our article on fluoride, reacting fluoride with calcium forms calcium fluoride, which is filtered out of the water as easy-to-dispose of compact solids and they can be implemented downstream of PFAS destruction.
New advances in desalination technologies (ultra-high pressure reverse osmosis, minimal liquid discharge (MLD) and zero liquid discharge (ZLD), such as our modular BrineRefine, XtremeRO, and our SaltMaker family of evaporator crystallizers) can help economically reduce PFAS wastewater volume and concentrate PFAS to a level that was previously unreachable. These modular mobile water treatment units can also be deployed to a PFAS wastewater site for onsite treatment. Our article on how to manage brine disposal & treatment provides a summary of management options.
Contact Saltworks for a detailed review of your PFAS project, risk and opportunities, as well as options to manage the result brine residuals.
Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.
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