Frequently Asked Questions: Removing Perfluoroalkyl Substances (PFASs) with Ion Exchange Resins

As municipalities discover that levels of perfluoroalkyl substances in water systems exceed new Federal Health Advisory levels, many questions arise. This guide can help you find answers to make your drinking water clean and safe.

What are the current Health Advisory Levels for perfluoroalkyl substances (PFASs) in drinking water?
Health advisory levels vary throughout the world. However, in May 2016, The US EPA issued Health Advisory (HA) levels of 70 parts per trillion (ppt) for PFOS and PFOA (perfluorooctane sulfonic acid and perfluorooctanoic acid, respectively). When both PFOS and PFOA are present at the same time in the water, the recommended combined health advisory level is 70 ppt.

What other names are used to refer to PFASs?
Polyfluoroalkyl substances, perfluorinated chemicals, fluorocarbon chemicals, and PFCs are additional names used. Purolite uses the terms PFASs and PFCs interchangeably.

What are short- and long-chained PFASs?
The term “long chain” is used to describe perfluoroalkyl sulfonic acids with a formula CnF2n+1SO3H where n ≥ 6 and perfluoroalkyl carboxylic acids with formula CnF2n+1COOH where n ≥ 7, and their corresponding anions. Examples of long-chain PFASs are perfluorooctane sulfonic acid, C8F17SO3H (PFOS), and perfluorooctanoic acid, C7F15COOH (PFOA). “Short-chain” PFASs refer to those compounds where n is < 6 and < 7 for sulfonic and carboxylic types respectively. Examples are perfluorobutanesulfonic acid (PFBS) and perfluorobutanoic acid (PFBA).

What are the most popular methods for removal of PFASs from water and waste water?
Granular Activated Carbon (GAC) is in widespread use. Synthetic adsorbent and ion exchange resins are also used. Capacity and leakage of PFASs into the treated water varies depending on the specific PFASs, the type of adsorbent used, and the empty bed contact time for which the system is designed.

What technology is available that can reduce PFASs to less than detectable levels?
Recent testing has confirmed that Purofine® PFA694E can remove fluorocarbon (PFAS) compounds to non-detect (ND) levels. Detection levels were 1 ppt for PFOA, 1 ppt for PFNA, 1 ppt for PFHpA, 4 ppt for PFBS, 4 ppt for PFHxS, and 5 ppt for PFOS.

Can ion exchange resin remove both short- and long-chained PFCs?
Yes. Ion exchange resin removes PFCs by two mechanisms—by ion exchange and by adsorption. GAC predominantly removes PFCs by adsorption. Recent tests show that resin can remove short-chained PFC compounds—PFBS and PFBA—to non-detect (ND) levels.

Does using Purofine® PFA694E cause a change in the pH and analyte concentration in the treated water?
Yes, temporarily. Purofine PFA694E is an anion resin and will change the anionic concentration of treated water for a brief period. For example, sulfate and alkalinity may be removed from the water and chloride released in its place. The duration of time for water chemistry changes is dependent on the concentration of total dissolved solids (TDS) of the water—higher TDS results in shorter periods. After this period, there will be no perceptible change in the background water chemistry. Usually such changes stop within a day or two.

Does background water chemistry affect operating capacity of Purofine® PFA694E?
Yes, anions typically found in water will partially impact the operating capacity. Therefore, quality variances in these anions must be considered in assessing operating capacity. Resin removes PFCs by both adsorption and ion exchange mechanisms. Work is underway to quantify such impacts.

Is Purofine® PFA694E an anion resin or adsorbent?
Purofine PFA694E is both a resin and adsorbent due to its hydrophobic properties. The product is supplied in the chloride form but supply in bicarbonate or sulfate form is possible on special request. When supplied in the bicarbonate form, there will be virtually no reduction in the pH of the treated water.

What are the design best practices for Purofine® PFA694E?
Purolite can provide details on acceptable designs. In general, PFA694E requires only 1.5 – 5 minutes of empty bed contact time (EBCT) vs. 12 – 25 minutes for GAC, making capital costs for an ion exchange solution about half of GAC.

Is Purofine® PFA694E suitable for use in POU/POE devices?
POU systems incorporating Purolite resin have obtained certification for potable use in Europe. Purolite can provide guidance on system design for POU or POE.

Is Purofine® PFA694E certified for use in drinking water?
Yes, Purofine PFA694E is certified under ANSI/NSF-61 for use in drinking water.