How do you destroy PFAS?

Only the most aggressive and energy-intensive tech­nolo­gies are capable of breaking down PFAS. Therefore, cost-efficient treatment options for large volumes of cont­a­m­i­nated water rely on coupling tech­nolo­gies that first separate and concen­trate PFAS to reduce the volumes and make destructive treatment tech­nolo­gies viable. 

Today, destruction tech­nolo­gies like elec­tro­chem­i­cal oxidation (ECO) and plasma have demon­strated abilities to breakdown the stubborn carbon-fluorine bonds, the strongest in chemistry, at the heart of all PFAS. Recir­cu­lat­ing PFAS in the environment from one media to another draws significant concern worldwide, as we risk re-releasing it back into our environment. Therefore, destruction is a critical step in solving the global PFAS crisis. To make destruction feasible, though, the entire treatment train must be optimized for maximum efficiency. 

Separate and Concentrate

In addition to conven­tional methods like GAC and AIX to reverse osmosis and beyond, our researchers have been rigorously testing new ways to separate and concentrate PFAS molecules, exploiting their affinity for air-water interfaces. One of these tech­nolo­gies relies on using air bubbles to “strip” PFAS out of water and into foams, which are condensed to generate hyper-concen­trated PFAS solutions.

Concen­tra­tion is a critical step in the destruction treatment train because it drastically reduces the volume of PFAS-laden effluent on its way to destruction. Together with EPOC Enviro, CDM Smith has been rigorously testing surface-active foam frac­tion­a­tion (SAFF®), which has been demon­strated to concentrate PFAS molecules up to 42,000 times with ongoing development to achieve concen­tra­tion factors closer to one million times. 

Destroy

There are numerous PFAS destruction tech­nolo­gies under development, conve­niently summarized in this ITRC PFAS Fact Sheet. Promising ex-situ destruction tech­nolo­gies that have progressed from bench- to pilot-scale include elec­tro­chem­i­cal oxidation, plasma and UV reductive, hydrother­mal, and super­crit­i­cal water oxidation. These approaches have success­fully degraded an array of high-concen­tra­tion PFAS at the laboratory scale. However, not all are suffi­ciently mature yet to assess PFAS treatment costs and overall effec­tive­ness with confidence at the field scale. 

Because they are energy intensive, it is important to selectively employ currently available destruction tech­nolo­gies on highly-concen­trated, low-volume targets. These include: 

• AFFF concen­trates 

• Groundwater within PFAS source areas

• Remediation waste streams (such as wastewater generated from regen­er­a­tion of GAC or regenerable ion exchange resin, foam frac­tion­a­tion-, soil washing-, rejected reverse osmosis- concen­trates, chemical or electro-coagulation)

• Landfill or biosolid leachate
   

Elec­tro­chem­i­cal Oxidation (ECO) 

Our researchers have proven elec­tro­chem­i­cal oxidation (ECO) to reduce high-concen­tra­tion PFAS effectively, typically achieving reductions of 90-99.999% in laboratory studies. 

ECO uses an elec­tro­chem­i­cal cell to generate an electric current between a reactive anode and cathode (the electrodes). The process degrades PFAS through two mechanisms: 

• Anodic oxidation (direct elec­trol­y­sis) – PFAS adsorb onto an anode surface and are destroyed directly at the electrode by a direct electron transfer reaction 

• Indirect oxidation – Strong oxidizing and nons­e­lec­tive radicals (such as hydroxyl, oxygen, sulfate and carbonate) are generated in-situ that react with, and break down, PFAS in the bulk liquid reactions. 

The ECO process system­at­i­cally breaks down PFAS, trans­form­ing it from a hazardous material into carbon dioxide, water and fluoride. In general, the direct electron transfer pathway is considered critical for oxidation of PFAAs, such as PFOA, PFOS, and perflu­o­robu­tane sulfonic acid (PFBS), while hydroxyl radical oxidation can break down AFFF and PFAS precursors. 
 

Choosing a Destruction Approach

Because of the emerging market for destructive PFAS tech­nolo­gies, they are often promoted hastily without demon­strat­ing complete deflu­o­ri­na­tion and without confidence the technology can meet stringent effluent discharge require­ments. The feasibility of these tech­nolo­gies must be carefully considered for each new application. To effectively develop a treatment train approach, technology compat­i­bil­ity, engineering constraints, and operations and maintenance require­ments must be considered. A thoughtful approach will ensure the system can meet required treatment volumes, rates, and discharge criteria.

Most destructive tech­nolo­gies for PFASs only work in specific conditions including extreme temperature or pressure, under caustic conditions, require high energy consumption, chemical additives, and other harsh treatment conditions. 

The development and commer­cial­iza­tion of PFAS destruction tech­nolo­gies will not be easy. Careful consid­er­a­tion and under­stand­ing of PFAS trans­for­ma­tion and deflu­o­ri­na­tion must be incor­po­rated into the technology evaluation for a particular site/application with thoughtful design of bench and pilot scale systems to demonstrate technology(ies) and incorporate economic feasibility in the selection process. 

Consid­er­a­tion of balanced technology benefits and limitations that should be discussed with technology providers include: 

• High energy demand and feasibility of high energy/cost at the scale required for the system

• Health and safety concerns

• Feasibility of operating large-scale systems, if required

• Incomplete PFAS destruction resulting in accu­mu­la­tion of fluorinated inter­me­di­ates that are generated but not measurable

• Feasibility of achieving stringent (i.e. very low) treatment require­ments, often a treatment train approach may be needed before effluent discharge

• Effec­tive­ness in destroying all PFAS chemicals, including short chain PFAS, which are generally harder to treat and precursors as sources of PFAAs

• Generation of non-PFAS toxic byproducts. For instance, perchlorate is known to be formed during elec­tro­chem­i­cal oxidation treatment due to the aggressive oxidation of chloride in the feedwater. Although perchlorate can be addressed easily, treatment systems must account for, and treat, perchlorate in the process

CDM Smith’s approach to assessing PFAS destructive tech­nolo­gies at a site includes treata­bil­ity testing at the bench-, pilot-, and full-scale levels, using three lines of evidence to confirm complete PFAS destruction. Our collab­o­ra­tion with univer­si­ties and research foundations allows us to explore the latest analytical methods for under­stand­ing the destructive mechanisms, kinetics, toxic inter­me­di­ates, and end products formation. The collab­o­ra­tion helps bring the most effective means and methods to our projects. We are working on advancing the science and engineering into compre­hen­sive treatment systems (e.g., treatment trains) to achieve a complete solution for PFAS-impacted waters.