A Holistic Approach to PFAS

Per- and poly-fluoroalkyl substances (PFAS) have been saddled with the moniker “the ubiquitous forever chemicals” because they are everywhere, and they last forever. This class of fluorinated chemicals is a non-naturally occurring substance that comes in many forms and has been found everywhere in our environment, especially our water supplies. PFAS chemicals and their brethren PFOS, PFOA, PFHX, and other varieties have been shown to be biologically active, remaining in the liver and kidney for up to seven years. They are teratogenic and are linked to a number of birth defects. As such, it is our responsibility as good stewards of our water supply to deal with these materials in such a way as to eradicate them, as much as possible, from our environment.

Stormwater management, groundwater treatment, and prevention of the spread of these chemicals into our water supplies should be paramount in our mission to provide safe drinking water now and into the future. This is a significant task, and we must tackle the problem with all the ammunition in our arsenal.

PFAS chemicals are a very complex group of long and short-chain fluorinated compounds and, as such, the complexity of the chemistry demands a complex solution. One of the popular choices in the treatment of PFAS contamination in stormwater and groundwater is a simple carbon adsorption system. Granular activated carbon (GAC) has been the treatment of choice for the management of PFAS contamination. It is low cost, readily available, and systems are simple to operate. Unfortunately, in most cases, carbon treatment alone is too simple a treatment system to remove the wide variety of contaminants that may or may not be present in the water.

Carbon adsorption is nonspecific for PFAS chemicals. Although carbon will remove a host of organics, nitrates, and some longer chain PFAS chemicals, it will allow inorganics and some shorter chain PFAS and PFOA chemicals to pass through unscathed, allowing these chemicals back into the environment. Furthermore, “carbon only” systems have a short life and require large amounts of carbon and, therefore, larger vessels. Frequent change-outs, disposal of the exhausted carbon by incineration, or regeneration of the carbon all add to the cost of this “simple” treatment method. Although carbon treatment systems are widely employed, they may not be the best solution and, in many cases, not the most cost-efficient solution to providing clean water.

The most effective PFAS treatment efforts use a holistic approach. It is important to first evaluate the source water to determine the type of fluorinated compounds that are present; there are more than 5000 species currently identified and that number is growing daily. Whether they are long-chain, short-chain, PFOA, PFOS, or other moieties, all play a critical role in choosing the right treatment system. Second, it is critical to understand the presence of other contaminants of concern that may be present. Organics and or heavy metals, such as selenium, arsenic, or mercury, will play a vital role in determining the most effective treatment system. Total suspended solids (TSS), total dissolved solids (TDS), and pH must also be considered when designing a treatment system. These contaminants of concern (COC) will compete with PFAS chemicals in the adsorption process, so their presence and concentrations are critical factors in determining the amount and types of media needed to remove not only the PFAS but the other contaminants as well.

Once you understand the raw water, a complete understanding of the target levels desired in the treated water is the next step. PFAS limits are yet to be established by the EPA, so to what level we need to remove these chemicals is not yet known. Many states are promulgating levels as low as 7 parts per trillion (ppt) with one state targeting 0 ppt as their treatment standard. It is critical to understand the treatment target in order to design a system that will consistently and cost-effectively meet the desired targets.

Using a holistic approach allows you to design a system that will not only remove PFAS chemicals but will also manage other COC, providing the best treatment solution. Clear Creek Systems has developed one such system—a multi-stage treatment approach designed to meet even the most stringent permit limits for stormwater and groundwater treatment applications.

A well-designed system must start with proper TSS management. Suspended solids will reduce the effectiveness of any media system, so the proper utilization of filtration, and in some cases chemical precipitation followed by filtration, is a critical first step in the treatment design. The lower the TSS, the better the media can perform, and the longer the media will last, providing better results at a lower cost.

Once the TSS has been managed, the next step(s) will be various media treatments designed to treat the specific contaminants in the wastewater source. At Clear Creek Systems, we evaluate the COC and utilize multimedia treatment such as organoclay, carbon, PFAS specific resins, mineral systems, and in some cases, ultrafiltration followed by R/O treatment, the latter being mostly employed in drinking water treatment.

Organoclay may be employed to treat oils and some heavy metals such as molybdenum or arsenic. Different clay species will treat for different contaminants, so it is critical we understand the contamination levels for all COCs. Organoclays will also remove a significant amount of PFAS from the water, allowing this first step in the treatment process a wide spectrum of functional use.

In most cases, we will employ carbon after the organoclay. Carbon is used to remove a variety of organics, reduce odor and color, improve taste, and eliminate much of the longer chain PFAS chemicals through adsorption. By preceding the carbon with filtration and organoclay media treatment, we can extend the life of the carbon and reduce the amount of carbon required in the system, thereby reducing the size of the vessels and the overall cost of the complete system. Since the carbon will last longer, we can reduce the number of carbon change-outs and thus reduce the cost of replacement and disposal of the exhausted carbon.

The next leg in the multistage treatment system is to employ PFAS specific single-use Ion Exchange resins. These resins are available from a wide variety of suppliers and are specifically formulated for PFAS chemicals and their brethren. Resins work by both adsorption and ion exchange and are highly effective in reducing contamination levels. Ion Exchange resins have a capacity for PFAS that is twenty times greater than granular activated carbon (GAC) allowing for a reduced volume of resin required as compared to GAC. Resins act as a polishing step to the previous organoclay and carbon media, assuring compliance with even the most stringent PFAS limits. Resins have been designed for specific chain lengths of PFAS compounds so the potential to focus on specific species of PFAS is possible.

Taking a holistic approach to PFAS management can allow for the development of a system that is effective, efficient, and specific to your treatment needs. Remember: PFAS present a very complex problem requiring a complex and complete solution.