The topic of PFAS contamination is heating up. Pressure is increasing; on regulators to adopt more stringent policies, and on water suppliers to find cost-effective solutions for removing PFAS from contaminated water supplies.
Because the potential health risks surrounding PFAS are high, managers and operators at water utilities are faced with becoming educated on PFAS, building trust with their communities, and juggling evolving regulations – all while simultaneously planning for and funding treatment systems to ultimately serve clean drinking water.
Below we outline current PFAS treatment technologies, implementation, and new options on the horizon as the final installment of our 3-part series, PFAS: Communication, Covering the Cost of Cleanup, & Treatment.
PFAS Treatment Technologies
The first step in choosing the right treatment technology is understanding what the options are, their pros and cons, and who each option is best suited for. Deciding on the treatment that is best suited for you will depend on the specifics of your situation, and it’s advisable to hire a technical expert or engineer to assess your circumstances and decide on the method. That said, before you hire an expert it may be helpful to understand the playing field.
PFAS treatment solutions include granular activated carbon (GAC) adsorption, ion exchange (IX) resins, and nano-filtration and low-pressure reverse osmosis (RO) membrane treatment processes.
Granular Activated Carbon (GAC)
Granular activated carbon (GAC) has a pore structure that results in a large surface area per pound of carbon source; when used in a filter, GAC can absorb dissolved species such as PFAS. GAC efficacy for PFAS removal depends on the source water quality and the presence of co-contaminants like natural organic matter (NOM) and other trace contaminants.
- Effective for treating a variety of volatile and synthetic organics including solvents, pesticides and hydrophobic long-chain perfluoroalkyl acids (PFAAs), especially perfluorinated sulfonates, such as PFOS.
- Low media costs per changeout, although the media life depends on the raw water quality and the treated water goals.
- GAC filter media can be backwashed, so it can treat source water with higher turbidity or precipitated iron.
- GAC systems can tolerate periodic doses of free chlorine to control biological activity in the feedwater supply system and GAC vessels.
- Typically less effective in treating shorter-chained PFAAs such as perfluorobutanoic acid (PFBA); often taller vessels, and more pairs of vessels, are required for GAC as compared to other treatment options.
- Long-chain PFAS like PFOA and PFOS
- Removing other organic compounds
- Energy efficiency
Ion Exchange (IX)
In an ion exchange (IX) system, contaminated water flows through a bed of media similar to a filter, and the unwanted charged contaminants in the feedwater are replaced with harmless compounds like sodium and hydrogen in cation resins, and chloride and hydroxide in anionic resins. Ion exchange resins that treat PFAS in drinking water applications are typically highly selective, single use resins that can last for 6-18 months depending on the flowrate, PFAS concentration and the presence of competing anions such as sulfates and nitrates. To assess treatment efficacy on a given source water, testing is strongly recommended to make accurate projections.
- Highly selective long-life resins provide good removal of short and long-chain PFAS.
- IX systems have a long resin service life, so they may foul prior to PFAS breakthrough or exhaustion; specifically, certain IX resins deteriorate in the presence of chlorine or other oxidants.
- There is no need for resin regeneration, meaning no contaminant waste stream to handle, treat, or dispose of.
- The lack of a disinfection residual can lead to challenges in controlling biological activity in the resin bed.
- Although its service life can be longer, IX replacement media tends to be more expensive than GAC
- Short-chain PFAS
- High capacity operations
- Preferential removal of just PFAS using selective resin
Reverse Osmosis (RO)
Membrane separation technologies such as nano-filtration and reverse osmosis (RO) can remove all PFAS tested very effectively from impacted drinking water. In these applications, the feed water is forced through a semipermeable membrane at high pressure (specific pressure is dependent upon the application), resulting in a high-quality finished water.
- Excellent removal of PFAS, including short-chain PFAS, can be attained using low-pressure RO (LPRO).
- LPRO is an effective option to remove a wide variety of PFAS compounds and other possible contaminants of concern and is often the most resilient to contaminant spikes in the incoming flow stream.
- Despite LPRO’s effectiveness, it is typically the costliest method for removal of PFAS due to high capital cost and energy demand.
- LPRO may be susceptible to fouling; therefore, an anti-scalant and/or a pre-treatment step may be required to minimize potential membrane clogging.
- Short-chain PFAS
- High concentrations
- Low water quality goals or MCLs
- Homeowners or small operations treating water at one faucet or location
Implementing Treatment Solutions
For all three technologies, bench-scale and/or pilot-scale testing is critical to confirm the viability of the solution for the site-specific water matrix, and for developing system design and cost performance parameters. This initial testing can help in identifying the most effective treatment approach, and can give insight into estimated breakthrough and anticipated changeout frequency. Additionally, it can uncover critical information about efficacy, potential for fouling, and long-term savings on operating costs. Both the initial cost of installment and on-going operations costs are highly variable, and are critical components of evaluating which technology is the right fit.
Each technology requires unique considerations for the items that make up the most significant proportions of life cycle costs, such as equipment cost, pumping requirements, operations and maintenance labor, and chemical needs.
- IX is typically more expensive than an equal volume of GAC, though IX requires smaller bed volumes for similar levels of treatment.
- Finding the balance between IX and GAC empty bed contact time (EBCT) and changeout frequency required to meet performance goals via pilot or bench-scale testing is critical to estimating operating costs.
- GAC and IX can be integrated within a utility’s existing treatment plant infrastructure. Even though many utilities use GAC or IX, potential liabilities associated with future disposal of spent media may be a concern.
Important to note that PFAS treatment technologies may or may not be effective for the removal of co-contaminants.
Research and development programs are evaluating emerging technologies to concentrate and then destroy PFAS without releasing harmful byproducts.
PFAS destruction technologies that have recently been demonstrated successfully at bench-scale include but are not limited to:
- Hydrothermal alkaline treatment
- High-energy electron beam
Destruction of PFAS has also been demonstrated successfully at the pilot scale using:
- Electrochemical oxidation
- Supercritical water oxidation
- UV-hydrated electron
The optimal destructive solution needs to consider the specific water quality, site constraints, disposal options and existing processes at each application. It is also essential that the solution does not simply transfer the PFAS from one environment to another (e.g. soil to air, water to watershed, water to landfills, etc.) - it must eliminate PFAS altogether in order to address the public health concern.
Funding options for water treatment solutions
Each water system will be faced with determining the right treatment based on the type of PFAS contamination they have. It is always advisable to hire a treatment expert who can match your site specifics with the right technology to eventually provide clean water to your community.
All that said, finding the right treatment method is only one piece of the larger puzzle of solving PFAS contamination. Another critical component is finding a way to fund the removal of these contaminants, which can cost millions of dollars. Some utilities are looking to shift the cost of clean-up to polluters. Read more about the cleanup process and determining accountability.