Innovative Low-Cost Sorbents for PFAS Remediation

Background:

Per- and Polyfluoroalkyl Substances (PFAS) are ubiquitous contaminants in the water environment. These compounds are detected in surface water, groundwater, drinking water and wastewater. Broadly speaking, PFAS can be divided into three groups: 1) Conventional PFAS, such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) representing long-chain perfluoroalkyl acids (PFAAs). PFAAs are perceived as end products of PFAS degradation. Due to their persistent, bioaccumulative, and potentially toxic nature, U.S. EPA recommended a health advisory level of 70 ppt for PFOA and PFOS. Several states in the U.S. have established maximum contaminant levels (MCLs) for different kinds of PFAAs and at even lower concentrations, like 10 or 20 ppt; 2) PFAS alternatives. These alternatives are supposed to replace PFOA and PFOS as production and use of these two PFAAs are disallowed; and 3) PFAA precursors. These precursor compounds can be degraded to PFAAs through abiotic and biotic pathways. In recent years, these precursor compounds have received increasing attention given the fact that they are widely detected in various environmental matrices. Without proper treatments, these precursors can serve as a source and reservoir of PFAAs and force PFAS remediation to be endless.   To remove PFAS from contaminated water, sorbents, such as granular activated carbon (GAC) and ion exchange resin have been investigated intensively. Among all sorbents, GAC has been used widely. Many communities have chosen the same approach after their drinking water is found to contain PFAS. GAC as a sorbent, retains basically everything: metals, organic matter, etc. in the incoming water. Specific to PFAS sorption, GAC has encountered one critical issue that is well-recognized: much lower efficiency in removing short chain PFAAs and PFAS alternatives than those of long-chain PFAS. It is unclear at this stage whether GAC is able to retain PFAA precursors in water. Additionally, the process of producing GAC is highly energy intensive and has drawn scrutiny and attention recently in terms of greenhouse gas emissions. Aside from drinking water, wastewater is known to contain numerous PFAS. The conventional wastewater treatment processes, such as activated sludge are unable to remove PFAS.   Oftentimes, the effluent is found to have higher concentrations of PFAAs due to the possibility of degradation of PFAS precursors during the treatment process. The PFAS-containing effluent or treated wastewater will lead to further contamination of the receiving environment if the PFAS are not removed.

Technology Overview:

To develop robust, versatile, and inexpensive sorbents that are able to sorb all types of PFAS in water, University at Albany researchers recently synthesized and characterized >10 sorbents. The synthesis methodology is rooted in a deep understanding of PFAS structure, chemical properties, and potential interactions between PFAS and a given sorbent. The initial screening test narrowed down the sorbents to three. Further test of the three, each at a dosage of 100 mg/L, demonstrated that the modified clay, among all sorbents synthesized and tested, had the highest removal of 9 PFAAs, GenX (PFOA alternative) and three precursors compared to GAC and powdered AC (PAC) from Calgon and a commercial AC-aluminum based sorbent. The removal by modified clay was fast and significantly higher than those of PAC. After four hours, the concentrations of all PFAS approached zero or non-detectable in the tested systems from an initial concentration of 10 ppb. For those with PAC, however, PFAS at the low end of ppt (ng/L) were still there. Additionally, the modified clay was highly efficient for sorbing one PFAS precursor, diPAP, for which the PAC was not very effective.   Other sorbents that stand out are modified GAC and PAC. Both modified GAC and PAC demonstrated better performances than the un-modified counterparts. Modified GAC has higher removal than GAC for all tested PFAS. Although PAC removed most of the PFAS tested, its sorption of diPAP was significantly lower than that of modified PAC. Batch adsorption experiments were carried out with various adsorbents, including commercial Fluoro-sorb and the University of Albany modified clay and modified PAC. This modified clay and PAC showed that at T=48 h, the concentrations of most PFAS in the liquid phase were less than 100 ppt, and especially for modified clay, most of PFAS were non-detectable. For Fluoro-Sorb 200, at T=48 h, most of PFAS in the liquid phase were still at a relatively high level. For example, at 48 h PFOA was ~ 2 ppb (Co=6 ppb), and PFOS was also ~ 2 ppb (Co=15 ppb). Compared to the removal efficiency the modified clay is much better.   Most recently, the team tested sorption capacity of the modified clay with varying initial concentrations for 12 PFAS. Samples were withdrawn at different time points. Interestingly, at 1 hour, almost all PFAS became non-detectable. The sorption capacity increased with the initial PFOA concentration in ppb. The same trend was observed for other PFAS. Modeling using total PFAS revealed that the total sorption capacity can be over 100 mg/g sorbent.   A preliminary cost analysis indicates that the modified clay costs around $750/ton. This only considers the reagents used in the synthesis, but not the electricity cost. The research team do not perceive a high energy cost since the synthesis process necessitates less than 100 °C, much lower than what is required to make GAC (400-800 °C). For comparison, the selling price of Filtrasorb 400 GAC is $5,770/ton. For MatCARE, it is $26,000/ton. Synthetic AC was reported to cost about $1,500/ton.

Advantages:

Lower cost, faster sorption, less energy intensive to produce, removes all tested PFAS whereas other sorbents do not.

Applications:

Removing PFAS in any type of water, drinking water, treated wastewater, use at large scale facilities and point of entry use.

Intellectual Property Summary:

Provisional patent

Stage of Development:

The initial batch tests were finished. The team are moving on to conducting a flow test. The technology is TRL 2-3. The performance and testing data referenced herein may be provided upon request. 
In summary, the University at Albany research team synthesized three promising sorbents toward PFAS sorption: modified GAC, modified PAC, and modified clay. These sorbents are novel, low-cost, and highly effective for removing different PFAS from contaminated water.

Licensing Status:

This technology is available for licensing.