It is anticipated that soon the United States Environmental Protection Agency (EPA) will announce final maximum contaminant levels (MCLs) in drinking water for six common per- and polyfluorinated substance (PFAS) compounds as a new National Primary Drinking Water Regulation to establish legally enforceable levels.
First proposed in March 2023 at 4 parts per trillion (ppt) for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) and a hazard index of one for any combination of the other four compounds—perfluorononanoic acid (PFNA), perfluorohexane sulfanate (PFHxS), perfluorobutane sulfanate (PFBS) and hexafluoropropylene oxide-dimer acid (HFPO-DA) (more commonly known as GenX chemicals). This announcement will also establish a timeline by which water treatment facilities will be held responsible for monitoring and then treating drinking water for PFAS and reducing these contaminants to the official MCLs.
Regulatory Burden
Utilities are expected to have three years to comply, which is not much time considering the demand on the supply chain that this regulation will stimulate. The EPA has estimated that about 66,000 public water systems alone will need to test for PFAS. Between 3,400 and 6,300 of those are expected to have levels that exceed the proposed MCLs and therefore require treatment. Depending on discount rate (3-7%), the U.S. EPA has estimated the annualized quantified rule cost to vary from $772 million to $1.2 billion. With just three years to monitor and potentially implement a reduction solution, there will need to be an intermediary or “quick step” to close the gap between monitoring and the capital expenses required for full bed installations. Other industry professionals have estimated an even greater cost of PFAS treatment.
Full-scale PFAS treatment systems will be major capital expenditures for the nation’s public drinking water systems. Significant funding from the Bipartisan Infrastructure Law (BIL) and Inflation Reduction Act (IRA) will be available, but this funding will be more difficult for smaller operators to access, primarily because they do not typically have the administrative staff to manage the paperwork required to procure government funding.
Furthermore, these small systems are less likely to currently have operation treatment trains that can handle PFAS, as opposed to larger municipalities that have previously installed carbon, ion exchange or reverse osmosis systems that can be adjusted considering the regulation. Additionally, operators both large and small that want to act quickly to mitigate PFAS for the protection of their users may not wish to wait for the time it will take to secure funding—or at the least, they will want to take some kind of action immediately while they are also seeking funding for a more comprehensive treatment system.
The Benefits of Powdered Activated Carbon
Powdered activated carbon (PAC) has long been a well-performing product for drinking water applications, especially for the removal of undesired taste and odor. While traditionally used to manage intermittent or emergency conditions, it is also proving to be suitable to reduce long-chain PFAS contamination to non-detectable levels. PAC can be applied through simple batch processing—direct dosing of PAC to the clarification process settling unit—with minimal additional equipment.
Powdered activated carbon does not require major infrastructure or physical space to deploy, so it can be implemented quickly. Strategically, it is attractive as a temporary solution because it gives facilities an immediate mitigation tool while they take the time to consider their options, apply for BIL and IRA funding and otherwise arrange financing for more permanent treatment strategies.
Unlike granular activated carbon (GAC), PAC offers lower barriers to entry and is rapidly deployable. In fact, many municipalities are already using it for other purposes (methyl-isoborneol [MIB] and geosmin) and may be able to adjust their dosing to treat PFAS contamination. By using higher quality carbon, the effectiveness of PAC for PFAS mitigation can be maximized, and the size of the dose requirement can be lowered. The best activated carbon to select is one with a broad profile of pore size distribution—a healthy variety of pore sizes, from micropores to macropores. For municipalities focused on sustainability, raw material can be catered to more renewable sources such as coconut and wood rather than coal.
Spent PAC is easily removed from the water through mechanical filtration. It must be noted that spent PAC cannot be reactivated and is normally removed as a part of the sludge blanket generated in the coagulation steps of treatment. Another advantage of batch processing is that the PAC is used for a short period of time and then discarded. As a result, there is little chance for bacteria multiplying within the carbon bed before it is removed.
PAC Offers Faster Adsorption Kinetics
Activated carbon works mainly through adsorption with attraction to non-polar species (organic materials). Through electrostatic interaction (Van der Waals forces), the long, non-polar chain (tail) of fluorine in PFAS pulls the PFAS molecules away from the water and onto the carbon particles separating the PFAS from the bulk phase water. GAC is also used for many water treatment applications, including PFAS mitigation, but it requires more infrastructure (filter beds, pumps, etc.) and cannot be as easily dosed as PAC can.
Additionally, PAC has a much smaller particle size than GAC, which results in faster adsorption kinetics. The diameter of PAC particles, and the length of the diffusion path, is 10 to 100 times smaller than GAC particles. Therefore, the rate of adsorption in water solution is much greater for PAC than for GAC. The decreased particle size also makes it easier to disperse the PAC and keep it suspended with agitation.
Long-chain PFAS, including PFOA and PFOS, are some of the most common PFAS found in drinking water and are two of the six PFAS proposed by the EPA for National Primary Drinking Water Regulation. Because PAC works well for long-chain PFAS, it is a good fit for the PFAS targeted by the EPA’s new regulation.
PAC Is Easily Accessible
Because of its ability to reduce PFAS in drinking water, PAC offers a simple and cost-effective solution that water treatment facilities can deploy quickly, inexpensively and effectively. This provides a flexible option for facilities eager to protect their customers from the effects of PFAS while our industry waits for final MCLs from the EPA, and until facilities can receive government funding for larger treatment infrastructure improvements.
