The documented performance of ion exchange (IX) resins for treating per- and polyfluoroalkyl substances (PFAS) offers new opportunities for more practical solutions in many applications. As water utilities and design firms evaluate treatment alternatives, and are being challenged by the space, cost, and time to install and implement solutions for PFAS, IX is showing its ability to reduce capital and operating costs compared to the conventional granular activated carbon (GAC) treatment approach.
The Growing Need For PFAS Treatment
A recent report by the Environmental Working Group cites the latest statistics on PFAS’ reach into everyday American life — drinking water systems serving an estimated 19 million people, in at least 610 locations across 43 states are known to be contaminated with one or more of the thousands of known PFAS compounds. Based on their widespread use across various industries, it is no surprise that many of these sites are associated with military bases, airports, industrial/chemical facilities, and firefighter training locations. The EPA has established a health advisory level of 70 parts per trillion (ppt) of combined PFAS compounds in drinking water due to links with cancer, developmental effects, liver damage, thyroid issues, and more. Recently, the federal Agency for Toxic Substances and Disease Registry proposed a more aggressive recommendation of 7 ppt for PFOS and 11 ppt for PFOA.
Confronted with this reality, water treatment utilities, private water treatment operators, and municipal leaders face difficult challenges related to public health concerns, the ever-changing regulatory environment for these persistent chemicals, and both the capital and operating costs of treatment solutions.
Another Option for PFAS Treatment
As municipalities sought ways to rapidly respond to addressing PFAS contamination in their source water, maintain use of their own wells, and quickly install treatment, GAC offered an early and proven option based on its known performance. However, the hydrophobic tail and negatively charged head structure of PFAS compounds (Figure 1) also makes them well suited for removal by IX.
Over the past few years, significant data has been generated by utilities, engineers, and resin manufacturers proving the ability of IX to remove PFAS down to non-detect levels for long periods of time.
Putting IX Resin Performance In Context
While the familiarity and acceptance of IX resins currently differs among regulators from state to state, and among utilities and operators, the EPA cites the efficacy of both GAC and IX resins for treatment of PFAS in drinking water:
- “GAC can be 100 percent effective for a period of time, depending on the type of carbon used, the depth of the bed of carbon, flow rate of the water, the specific PFAS you need to remove, temperature, and the degree and type of organic matter as well as other contaminants, or constituents, in the water.”
- “Like GAC, anion exchange resin (AER) removes 100 percent of the PFAS for a time that is dictated by the choice of resin, bed depth, flow rate, which PFAS need to be removed, and the degree and type of background organic matter and other contaminants of constituents.”
Section 3.1.3 (Ion Exchange) of this fact sheet published by the Interstate Technology Regulatory Council outlines the physical performance characteristics and efficacy of IX resin for PFAS removal in water treatment. This case study also provides a look at the first water treatment utility to reduce PFOS and PFOA to non-detect levels (approx. 4 ng/L to 6 ng/L) instead of merely complying with the EPA’s current Health Advisory Limit (HAL)of 70 ng/L. In that application, IX was initially chosen to polish the throughput of the GAC systems, but subsequently proved its ability to carry the entire treatment load.
With validated effectiveness and performance guarantees for the life of the resin offered by suppliers, IX treatment of PFAS can now be considered by regulators, engineers, and utilities as an effective solution.
Design Considerations In Choosing A PFAS Treatment
When evaluating the treatment options for PFAS, the major difference between the two approaches lies in the cost of construction and cost of operation, which is a function of removal performance. The main items to consider are:
- Available Space. The treatment system may need to be installed at an existing wellhead, where site space may be constrained due to the preexisting size of the structure or its proximity to property lines or other structures in highly developed neighborhoods.
- Lifecycle Cost. Both the capital cost (installed cost of the treatment system infrastructure) and the operating cost (cost for replacement of media or resin based on the performance life) should be evaluated together to determine the option resulting in the lowest possible lifecycle cost.
- Wastewater Management. Each treatment option has different requirements for implementation, system start-up, and operation that will result in a liquid waste stream. Though the liquid waste stream is non-hazardous, the wastewater generated must be managed and may require additional infrastructure.
Better CAPEX, OPEX With IX
The shorter empty bed contact time, smaller vessels, longer life, and minimal backwash requirement of IX resin mean the solution offers an attractive alternative for end users and engineers when investigating PFAS treatment, especially when forced to fit treatment equipment into existing infrastructure and operations. While every water quality and specific site is unique, PFAS treatment with IX resin is proving to offer a lower overall cost of treatment in many evaluations.
Editor's Note: Scranton Gillette Communications and the SGC Water Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the editorial teams of Water & Wastes Digest, Water Quality Products and Storm Water Solutions.
