Pretreatment Systems Enable Complete And More Economical PFAS Solutions

By Russ Swerdfeger

As 2027 per- and polyfluoroalkyl substances (PFAS) reporting deadlines rapidly approach, water utilities are heavily investing in PFAS removal and destruction capabilities. There are various effective methods to remove PFAS from our water, but no matter the technology selected, this step is usually one part of a much larger treatment train. Many of these treatment trains have steps in place to remove some organic materials present in water, however, an incomplete or partial organics removal step may be inadvertently sabotaging downstream PFAS systems and can lead to higher utility operational costs.

Dissolved organic carbon (DOC), along with other contaminants, occur naturally in many source waters and can present potential challenges to PFAS removal, especially if a media-based system is deployed. These charged organic compounds can interfere with many PFAS treatment solutions, like granular activated carbon (GAC) and anion ion exchange, as they compete with PFAS for the same removal mechanism. PFAS' fluorinated tail and charged head group stick to adsorption media's surface and active sites. DOC, and other contaminants, will attach to these same sites when it encounters treatment media. This competition leads to higher operational costs through more frequent media change-outs in order to sustain PFAS removal targets in the treated water.

For operators looking to optimize their PFAS removal systems, controlling the presence of DOC offers an approach to minimizing operational costs due to GAC reactivation and ion exchange media change-out.

How DOC Impacts The PFAS Treatment Approach

Across many regions of the world, water utilities are turning to more complex surface water sources to serve their populations. Some of these surface and ground waters will contain a long list of contaminants to treat, including PFAS compounds, which adds layers of complexity to the treatment processes deployed.

Organic matter ends up in water sources through natural and man-made processes, and in many regions the level of organic materials in drinking water are their own regulated contaminant. DOC levels can also be variable and have seasonal high and lows, which creates an additional challenge for plant operators who are looking to optimize their treatment trains.

Conventional treatment approaches typically rely on chemical coagulation to remove organic matter. As organic levels increase, the typical operational response has been to add more chemical coagulants. Throwing more chemicals at these contaminants will provide some improvement in organics removal. However, ensuring that chemicals remove enough organic matter can be costly, and can lead to unforeseen downstream impacts. As the majority of coagulants are acidic, the added chemical load will also likely impact treatment plant performance and distribution system chemistry. Furthermore, many coagulation processes reach an upper limit of effective organic removal, which is likely not sufficient to maximize the operational life of a PFAS removal media.

To provide a sense of the economic impact of GAC change-out occurrence, consider a plant with approximately 450,000 lbs. of GAC media using a 15-minute empty bed contact time (EBCT) design. Reactivation of GAC typically ranges from $0.90 to $1.50 per pound, with the average cost being $1.20 per pound. This puts the cost of reactivating the entire inventory of GAC once over $500,000. Extending the time between reactivations in this example by six months can be worth up to $230,000 of cost savings. As more GAC systems are commissioned, the demand for reactivation capacity will obviously rise and operators should expect the cost of reactivation to increase into the future.

Steps Operators Can Take To Restore Efficiency To Their PFAS Solution

Winning the fight against forever chemicals means enabling the whole treatment train to achieve reliable and economic treatment, not just adding a PFAS removal step. Proven treatment options are available for operators to implement and meet the PFAS challenge.

For more than two decades fluidized bed ion exchange (FBIX) processes have offered a way to reliably remove organics and other contaminants early on in a treatment process. Typically deployed as the first step in a treatment train, FBIX processes reliably remove their target contaminants with minimal impact from the typical seasonal variability we see in water temperature, pH, and alkalinity. These processes can be designed with a single resin to target DOC or a blend of resins specifics for other target contaminants such as nitrates and sulfates. FBIX processes are designed with resin regeneration functionality, which generates less waste than a typical media filter and uses far less power when compared to high pressure membrane processes like nanofiltration and reverse osmosis. When targeting organic removal, FBIX systems using anion resin target negatively charged, lower molecular weight organics which tend to be the most challenging to remove by chemical coagulation.

An obvious concern would be PFAS removal by an anion resin in the FBIX step. While one will remove some PFAS species, other more complex source water has orders of magnitude more natural DOC than PFAS on a mass basis. Due to this, the FBIX resins will not remove a meaningful amount of PFAS. Rather, it will be more selective for those more abundant organic compounds. Eliminating the competing species of organics before the PFAS removal step enables lower overall operating expenses and extends the time between media change-outs. 

As utilities prepare for the impending reporting deadlines, some are treating PFAS removal as an isolated problem at the end of a treatment train. While this may provide a short-term fix, efficient long-term PFAS treatment solutions should factor in the full treatment train for maximum efficiency. Addressing DOC further upstream of the treatment process will enable water utilities to get the most out of their PFAS removal media at lower overall operational costs and the technology available to achieve this objective exists today.

Russ Swerdfeger is the Head of Marketing and Strategy at IXOM Watercare. He can be reached at russ.swerdfeger@ixom.com. For more information about IXOM Watercare, visit https://ixomwatercare.com/.