Treating Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) Contaminated Wastewater and Landfill Leachate
4 October 2019
- PFAS are detected in wastewaters and landfill leachate due to their widespread uses in consumer and industrial products. PFAS do not degrade in traditional pathways and pose both human health and ecological risks.
- Three existing options for removing PFAS from wastewaters: granular activated carbon (GAC), ion-exchange (IX) resins, and high-pressure membrane filtration of nanofiltration and reverse osmosis (RO). The treatment system needs to be engineered carefully with the consideration of specific wastewater chemistry, co-contaminant removals, and the pros and the cons of these treatment options.
- The disposal of PFAS-contaminated GAC, IX resins or PFAS-concentrated brine may pose secondary risks and should be considered.
- New advances in desalination technologies can help reduce PFAS treatment and disposal costs: ultra-high pressure reverse osmosis, minimal liquid discharge (MLD) and zero liquid discharge (ZLD).
PFAS the “Forever Chemicals”
Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) are a group of man-made carbon-fluorine chemicals produced since the 1940s. They were widely used in nonstick 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 ever created, which results in PFAS not degrading naturally or easily. As such, PFAS are often called the “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 to name a few. The U.S. EPA is taking action by proposing regulations to protect drinking water and to cleanup PFAS-contaminated water sources.
Existing Treatment Options for PFAS Contaminated Waters
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 price tag. 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 wastewater composition is more complex than the “clean” drinking water and comprise co-contaminants besides PFAS. The presence of the co-contaminants will impact the method selection, the treatment system sizing and the eventual costs. For example, landfill leachate has co-contaminants of organics, inorganics and volatiles, in addition to PFAS, requiring removal.
The pros and cons for the three industrialized PFAS removal methods are summarized in the below table.
|Granular activated carbon (GAC)||
• Reduce PFAS to ng/L level for drinking water.
• Effective for long-chain PFAS removal.
• 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).
• Effective for anionic and long-chain PFAS removal to ng/L level.
• Higher adsorption capacity and significantly faster reaction kinetics compared to GAC.
• 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.
|Nanofiltration or reverse osmosis||
• 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.
• 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.
Technologies to permanently and economically treating PFAS wastewater
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. 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 the volume and the flowrate of PFAS wastewater are large. 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.
New advances in desalination technologies (ultra-high pressure reverse osmosis, minimal liquid discharge (MLD) and zero liquid discharge (ZLD), such as our modular BrineRefine, Extreme Reverse Osmosis, and SaltMaker evaporator crystallizer) can help economically reduce PFAS wastewater volume and concentrate PFAS into 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.
Please feel free to contact Saltworks for a detailed review of your PFAS project, risk and opportunities, as well as options to manage the result brine residuals.