There is no magic bullet in PFAS, but a well-designed system will provide clean water for years to come.
By Phil Farina BS, BA, MS, MBA
In the first part of this article (Waste Advantage Magazine, April 2022), we discussed what you need to do before you start managing PFAS at your facility—meaning, there are several steps to take before you jump to a decision on PFAS treatment options. To review: first, understand the composition of the water through analysis to determine not only the PFAS species present, but also to understand what competing contaminants are present that will complicate the treatment protocol. Next, understand the source water and the final disposition of the water to be treated. Is this groundwater or drinking water? Is this a long or short-term project? What is my treatment target level? The answers to these questions will guide you to better define the type of treatment to be employed.
Now that we understand the water characteristics and have defined the treatment requirements, we need to evaluate the treatment options. The most common treatment options employ specific media either singly or in combination. These include carbon (in the form of granular activated carbon or GAC), resins (specifically manufactured materials), and organoclays (surface-modified natural materials). These different media represent the workhorses for PFAS management. Let’s look at each individually.
Granular Activated Carbon
Carbon, better known as GAC comes from two main sources. Coconut fiber is a naturally occurring and renewable resource, or bituminous coal, which is a naturally occurring mined material. Both materials will remove PFAS through absorption. These materials act as a surface absorption media through the deposition of PFAS across the active sites on the surface of the granule. This is a relatively strong bond, however, under certain circumstances, such as low pH, GAC will give up some PFAS. It should be noted that bituminous GAC is the preferred media over coconut sourced GAC since it has a higher absorption capacity and a stronger affinity for PFAS molecules.
GAC is the essential workhorse for PFAS remediation. It is very well understood, is relatively low cost, and can be employed quickly with mostly satisfactory results. However, GAC does have its shortcomings.
Treatment systems that employ GAC need to be sized to accommodate a 20-minute empty bed contact time (EBCT). EBCT is the measure of the time during which water to be treated is in contact with the treatment medium in a contact vessel, assuming that all liquid passes through the vessel at the same velocity. EBCT is equal to the volume of the empty bed divided by the flow rate. This requirement has been defined by several states such as Massachusetts and Michigan as the minimum contact time required to remove PFAS using a GAC media. Second, the media is most often employed in a lead/lag configuration, resulting in a system that can be significant in size and requires a large quantity of media. For example, a flow rate of only 200 GPM requires 535 cubic feet of media contained within two tanks 6 feet by 12 feet set up in series. This allows for some freeboard room in the tanks to allow for expansion and possible backwashing should the media be contaminated by TSS inflow. That can be a large footprint.
GAC also can be supplied as either virgin or regenerated media. Both sources have a similar action, but the absorption capacity of regenerated material has about 80 percent of the capacity of virgin GAC. Regenerated GAC is lower cost, but if the project is of longer duration, the cost differential can be quickly consumed by the frequency of change out of the media. Knowing the timeframe of treatment will help define if regenerated GAC will be cost-effective.
GAC media is very effective for mid-range and longer chain species of PFAS. It will pull out short-chain species, but may release them in preference of longer chain species as the media approaches capacity, resulting in a more frequent changeout schedule. So, we see the money spent in defining the PFAS speciation in the first place, can be very beneficial in determining the life expectancy of GAC media.
When considering GAC as the primary media in an application, the exhaustion curve must be evaluated to determine the fully loaded cost of treatment. As we said, GAC is employed in a lead/lag configuration where the first vessel does the brunt of the work in removing PFAS, while the second vessel acts as a backup. The first vessel will, therefore, reach exhaustion significantly sooner than the second vessel. When this occurs, the procedure is to change out the first vessel with new media and change the process flow such that the second vessel is now the first vessel. In this way, you can get the most use of the media, reducing the total cost of ownership. This does, however, increase the initial cost of installation so that the proper valves and piping are installed to accommodate changes in the flow direction.
Some advantages of GAC media are that it is readily available, carries no tariff, and can be disposed of either in special PFAS permitted landfills or via incineration. GAC should be considered as a stand-alone or as part of a multimedia treatment system.
Resins
Resins are the next step up in media for PFAS management. Resins are a polymer-based manufactured bead material whose surface has been modified to function as an ion exchange media for the removal of PFAS from water. The ion exchange mechanism exchanges a chlorine molecule and replaces it with the PFAS molecule. This is a very strong bond and, as such, can withstand various changes in pH, keeping the PFAS molecule from being released back into the water.
The surface of the bead can be modified to accommodate a wide variety of PFAS species, giving resins the ability to function in complex applications. Some resins also have an adsorption mechanism, meaning that PFAS is not only removed by surface action, but that some PFAS may also enter the bead and become entrapped, increasing the holding capacity of the resin. In fact, most resins can hold up to 10 times as much PFAS contaminants as GAC. As an example, one resin manufacturer shows that GAC may have a capacity of 30,000 to 50,000-bed volumes whereas a resin system has a capacity of 500,000 to 800,000-bed volumes. GAC may need to be changed out every four to six months, whereas the resin system may last two to three years before a change out (assuming ideal conditions).
Another advantage of resins is the shorter EBCT required to achieve the desired goal. GAC requires 20-minute EBCT while most resins will be effective with 5 minute EBCT and in some cases 2.5 minute EBCT. This results in a much smaller system requirement.
The quick action of resins and the higher holding capacity also help to achieve a more effective removal of PFAS from the source water. GAC can easily achieve treatment levels down to 7 PPT, and in some cases, to non-detect levels (currently < 2PPT). Resins, however, achieve non-detect results consistently and for longer periods making resins highly competitive with the lower initial cost of GAC.
Many system designers will employ both GAC and resin in their system design, especially if the treatment system is permanent and the water source is complex. The GAC media will remove hydrocarbons, oils, and VOCs as well as PFAS, allowing the resin to focus solely on PFAS contamination. In this way, the treatment system will consistently reach levels of non-detect that is desirable for drinking water applications.
As far as disposal of exhausted resins, landfill disposal in permitted landfills is easily accomplished. Recent approvals by the regulatory agency allow for exhausted resins to be used as fuel in cement kilns, making disposal more convenient, lowering the cost, and assuring complete destruction of the PFAS contaminated resins.
The use of resin media is not without concerns. Competing contaminants include sulfates, nitrates, hydrocarbons, and chlorine. TSS will also negatively impact any media whether GAC, resin, or organoclays and must be removed before being introduced to any media. Again, knowing the full analysis of the water before designing a PFAS treatment system will allow one to include any pretreatment necessary to protect the resin. In many cases, filtration via sand media, bags, or cartridges can be employed to manage TSS. Nitrate, sulfate, and hydrocarbons may be removed by other media designed for such contaminants. With PFAS it is important to protect the media from secondary contaminants to prolong the effectiveness of the treatment.
Another issue with resins is availability. Since resins are not made in the U.S., they must be imported from China, Europe, or South America making them subject to the whims of politics, expensive transportation, and punitive tariffs. GAC is readily available while lead times for resins may be as long as six to 14 weeks depending on the supplier and volume required. Resins are much better for long-lasing systems, such as drinking water applications or multi-year pump and treat groundwater applications. They are not a media of choice for short-term remediation projects. Some resins can be regenerated either onsite or returned to the manufacturer for regeneration.
Organoclays
The last media we will discuss are organoclays. These are naturally mined materials in the form of bentonite or zeolite particles whose surface has been chemically altered to absorb PFAS molecules. Organoclay has a unique structure in that the clay is made op of sheet-like particles layered on top of one another much like a stack of paper. When exposed to water, these sheets expand, increasing the surface area of the particles. PFAS gets trapped within the layers, causing further expansion, allowing even more PFAS molecules to become entrapped. This mechanism gives organoclays an impressive carrying capacity for PFAS contaminants.
Organoclay will also absorb hydrocarbons, oils, and some heavy metals as well as PFAS, making them a perfect material to use in conjunction with either GAC or resins as part of the pretreatment. They can also function alone or may even be blended with GAC to improve GAC’s overall performance. Organoclay functions via ion exchange as well as absorption, providing a dual-action mechanism. This reduces the EBCT to five minutes.
Organyclays are especially effective in removing PFOA, PFOS, FTCA, FTSA, FTOH, and PFCA from source waters. They are effective in managing both long and short-chain species and are very useful for managing highly branched chain species, making them a well-rounded media option. Due to the specific gravity of organoclay being twice that of GAC, and organoclays’ high working capacity, you require less volume of media to achieve the same results as with GAC.
Disposal is accomplished via a permitted landfill or incineration. Organoclays are readily available and are priced very competitively to GAC.
Other Possible Solutions
Media is the workhorse for most PFAS applications. Reverse osmosis can also be used as well as electrocoagulation. These are well-known technologies and can be effective in removing PFAS, but in most cases, are more costly than media systems, require a higher initial investment, and require significant manpower for operations. They are not desirable for short-term treatment applications, but are most frequently added to an existing drinking water treatment system. They also create a highly concentrated by-product that is rich in PFAS, which still has to be disposed of. This material is usually disposed of by incineration. Unfortunately, incineration has fallen out of favor recently as many permitted PFAS incinerators have been decertified, reducing the available incineration sources and driving up the cost.
There is much ongoing research, especially in nano-filtration, and PFAS destruction technologies where the fluorine bond is broken, creating much shorter chain molecules less likely to be environmentally damaging. We also have research in biological degradation, although, so far, no effective bugs have been found to consistently reduce PFAS.
Know Your Process
So, in conclusion, it is important to first know your water well as to both the species of PFAS contained within and the different competing contaminants to be dealt with. Second, define your goals to understand if this is a long or short-term project, drinking water or remediation groundwater application, and what level of treatment is required. Finally, work with a collaborative technology-agnostic systems supplier who will guide you on your quest for the best system for your specific application. There is no magic bullet in PFAS, but a well-designed system will provide clean water for years to come. | WA
Phil Farina, BS, BA, MS, MBA, is Midwest Business Development Manager for Clear Creek Systems, Inc. Phil has more than 35 years of experience in the design and implementation of water treatment systems. Phil has extensive knowledge in managing PFAS contamination, remediation of groundwater, and Coal Combustion Residual projects. He manages new market development and market growth strategies in the Midwest. Phil’s technical expertise includes media technology, solids removal, mechanical solids separation technology, and water treatment in all industries, especially industrial, power, landfill, and construction. Phil can be reached at (419) 346-8848 or e-mail [email protected].