Addressing Per- and Poly-Fluoroalkyl Substances Through Source Water Assessments and Advanced Treatment Using Powdered Activated Carbon, Granular Activated Carbon, and Ion Exchange—

FWRJ Addressing Per- and Poly-Fluoroalkyl Substances Through Source Water Assessments and Advanced Treatment Using Powdered Activated Carbon, Granular Activated Carbon, and Ion Exchange

Samantha Black, Katie Walker, Gwen Woods-Chabane, Pete D’Adamo, and Dell Harney

Per- and poly-fluoroalkyl substances (PFAS) are manmade fluorinated compounds of emerging concern in the water industry. The PFAS are persistent and stable in the environment due to the strong chemical bond between carbon and fluorine atoms. They have been used largely for their water- and oil-repellent properties in several applications, including consumer products and aqueous film-forming foam (AFFF) to fight petroleum-based fires.

Communities in other countries and across the United States, including the City of Greensboro (city), N.C., have detected PFAS in drinking water supplies, typically at nanograms per liter (ng/L) concentrations. Elevated levels can be associated with facilities that use or manufacture these chemicals, such as airports (both domestic and military) and firefighting training facilities, as well as disposal sites of PFAS-contaminated wastes.

City of Greensboro Mitchell Water Treatment Plant

The city operates the Mitchell Water Treatment Plant (WTP), a 24-mil-gal-perday (mgd) conventional treatment facility. A schematic of the Mitchell WTP processes is provided in Figure 1. One of the city’s long-term goals is to provide a robust and flexible advanced treatment process capable of treating both emerging and regulated contaminants, and one family of emerging contaminants includes PFAS. The U.S. Environmental Protection Agency (EPA) has established a lifetime health advisory level (LHAL) of 70 ng/L for the sum of two PFAS: perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The PFOS and PFOA have been detected at trace concentrations in the city’s water supply at the Mitchell WTP, along with other PFAS. The LHALs for other PFAS are anticipated in mid-2022 and it’s expected that EPA will publish additional PFAS regulations in the next year.

Source Water Assessment

During sampling, as part of the third Unregulated Contaminant Monitoring Rule (UCMR) from 2013 to 2015, some of the city’s water samples had combined levels of PFOS and PFOA that exceeded 100 ng/L. These findings led to a two-year watershed investigation to identify hotspots of PFAS contamination in the city’s raw water supply. This two-year study included monthly sampling of 30 sites throughout the city’s watershed, such as lakes that supply raw water to WTPs, streams that discharge into these lakes, ponds near potential

Samantha Black, Ph.D., P.E., is a water treatment process engineer and associate at HDR in West Palm Beach. Katie Walker, P.E., is a drinking water lead and associate at HDR in Raleigh, N.C. Gwen Woods-Chabane, Ph.D., is a drinking water quality lead and senior professional associate at HDR in Portland, Ore. Pete D’Adamo, Ph.D., P.E., is a water treatment technical lead and principal professional associate at HDR in Vienna, Va. Dell Harney is the water supply manager at the City of Greensboro in Greensboro, N.C.

Figure 2. Per- and Poly-Fluoroalkyl Substances Speciation from a Stream Near Aqueous Film-Forming Foam Discharge Site Within the Vicinity of Historical Manufacturing Activities Figure 3. Powdered Activated Carbon Jar Testing Results

PFOS + PFOA Concentration (ng/L) 100

80 60

40 20

0 Water Source: RWPS Doses: 10 mg/L, 20 mg/L, 30 mg/L Contact Time: 1 min

RWPS No PAC 10 mg/L 20 mg/L 30 mg/L EPA Health Advisory Level

WC 800 Sample WC 1000

40 35 30 25 20 15 10 5 0

Total PFAS Raw Water Filtered Water

PFOS+PFOA

Figure 4. Full-Scale Powdered Activated Carbon System Results Figure 5. Total Organic Carbon Results From Granular Activated Carbon Column Effluent

2.0 UC1240LD F400 Aquasorb F23 Norit 400 Average Column Influent TOC

TOC (mg/L as C)

1.6

1.2

0.8

0.4

0.0

0 10,000 20,000 30,000 40,000 50,000

Bed Volumes Processed

contamination sites, historical fire sites, and groundwater wells. Figure 2 presents a summary of individual PFAS species identified during the study from a small stream near where AFFF has been discharged and where manufacturing used to occur. A majority of the total PFAS concentration is comprised of PFOS, which is found in AFFF and manufacturing.

One of the major benefits of the source water assessment was identifying potential contamination sites and collaborating with stakeholders, such as the local fire department, airport authority, and airport fire department, to reduce AFFF discharge and provide an open line of communication between stakeholders and the city. Since the completion of the source water assessment, PFAS levels detected by the city are well below the health advisory level.

Per- and Poly-Fluoroalkyl Substance Treatment

One of the first steps needed to identify an optimal PFAS treatment process is an evaluation of technologies using site-specific conditions. Research to date has shown that PFAS treatment effectiveness may vary, depending on the water source, pretreatment processes, and other operational conditions; therefore, a technology that works for one utility may not work for another. Additionally, treatment effectiveness is highly dependent on feed water quality. Bench and pilot testing under site-specific conditions prior to fullscale design of PFAS treatment systems is crucial to determine the most cost-effective treatment process.

Powdered Activated Carbon

In 2018, the city and HDR evaluated the effectiveness of powdered activated carbon (PAC) for PFAS removal in a jar test setting. The purpose of testing PAC was to quickly implement a PFAS mitigation strategy that would lower PFOS and PFOA levels to below EPA’s LHAL. In 2018, the city installed a temporary PAC system to remove PFAS at its Mitchell WTP. The PAC system has demonstrated partial PFAS removal, but it’s messy and associated with operational challenges, including increased

residuals production. The city desires the design and construction of a permanent, fullscale advanced treatment process to provide permanent PFAS removal from its water supply. Prior to full-scale installation, two PAC types of evaluations during jar testing were used to determine the efficacy of PAC doses and contact times at various PFAS levels. Doses of 10, 20, and 30 milligrams per liter (mg/L), and contact times of one minute (simulating PAC addition at the Mitchell WTP) and 30 minutes (simulating addition at the raw water pump station) were evaluated. Figure 3 presents results of jar testing evaluating two PAC types (the Watercarb 800 and Watercarb 1000), both manufactured by Standard Purification. At the time of testing, the PFOS+PFOA level was 88 ng/L, which was slightly higher than the LHAL, and there was minimal difference between the two PAC types. The PFAS removal increased as PAC dose increased, but not linearly. Although not presented herein, there was negligible difference between a contact time of one minute and 30 minutes; therefore, the city Continued on page 12 Florida Water Resources Journal • July 2022 11

Continued from page 11 opted to install the system at the Mitchell WTP.

Figure 4 presents results from full-scale PAC use using the Watercarb 800 product at a dose of 20 mg/L. At the time of sampling, the raw water total PFAS level was 34 ng/L and the PFOS+PFOA level was 20 ng/L. The PAC addition resulted in a 42 percent reduction of total PFAS and a 38 percent reduction of PFOS+PFOA.

Rapid Small-Scale Column Testing

Rapid small-scale column testing (RSSCT) was performed to evaluate multiple granular activated carbon (GAC) media and ion exchange (IX) resin, in parallel with controlled laboratory conditions. The RSSCT is a proven, quick, and effective method for evaluating the treatability of PFAS using various GAC media prior to pilot testing and full-scale design. These are continuousflow column tests where reduced GAC or IX particle sizes result in experimental conditions, with shorter empty bed contact time (EBCT), operation times, and column lengths, compared to pilot- or full-scale contactors. These conditions allow for much faster assessments of GAC and other media performance than equivalent testing with pilot- or full-scale evaluations.

Toward the end of 2021, pilot testing commenced to determine the optimal full-scale treatment technology. The pilot protocol was developed based on results from laboratory bench-scale testing.

Granular Activated Carbon

A suite of water quality parameters was monitored throughout bench-scale GAC testing. For brevity, only total organic carbon (TOC) and PFAS are presented herein.

Figure 5 presents TOC results from the GAC columns. Four GAC media types were evaluated: S Calgon F400 S Jacobi Aquasorb F23 S Evoqua UC1240LD S Cabot Norit 400

The average influent TOC level measured in the drums was 1.3 mg/L, and ranged from 1.2 to 1.8 mg/L. The GAC media removed roughly 0.5 mg/L up to about 10 to 15k bed volumes (BVs), but demonstrated little removal by 50k BVs. The Evoqua, Calgon, and Jacobi carbons provided slightly better TOC removal, compared to the Cabot carbon.

Figure 6 presents a summary of PFOS+PFOA removal capabilities by the four GAC media. Removal of individual PFAS are provided for each media type in its respective subsection. Generally, the Jacobi Aquasorb F23 provided the best PFOS+PFOA removal relative to the other GAC media tested, although the Calgon F-400 media also provided adequate removal. The Calgon F-400 provided the best TOC removal, compared to the other GAC media.

Figure 7 presents total PFAS removal as a function of BVs processed using the four different GAC media. Similar to the PFOS+PFOA results, the Jacobi and Calgon carbons performed better than the Evoqua and Cabot Norit carbons. The Calgon media provided superior total PFAS removal, compared to the Jacobi media, due to the higher removal of shortchain perfluorobutanoic acid (PFBA) and

Evoqua UC1240LD Calgon F-400 Jacobi Aquasorb F23 Cabot Norit GAC400

0 10,000 20,000 30,000 40,000 50,000 Bed Volumes Processed

Figure 6. Perfluorooctanesulfonic Acid and Perfluorooctanoic Acid Removal Using Granular Activated Carbon Figure 7. Total Per- and Poly-Fluoroalkyl Substances Removal Using Granular Activated Carbon

Total PFAS Removal (%)) 100% 80% 60% 40% 20% 0% Evoqua UC1240LD Calgon F-400 Jacobi Aquasorb F23 Cabot Norit GAC400

0 10,000 20,000 30,000 40,000 50,000 Bed Volumes Processed

PFOS PFOA PFBS PFHxS PFHpA PFHxA

100%

80%

Removal (%) 60%

40%

20%

0%

-20% 0 10,000 20,000 30,000 40,000 50,000 Bed Volumes Processed

Figure 8. Individual Per- and Poly-Fluoroalkyl Substances Removal Using Granular Activated Carbon (Evoqua UC1240LD) Figure 9. Individual Per- and Poly-Fluoroalkyl Substances Removal Using Granular Activated Carbon (Calgon F-400)

PFOS PFOA PFBS PFHxS PFHpA PFHxA

100%

Removal (%) 80%

60%

40%

20%

0%

0 10,000 20,000 30,000 40,000 50,000 Bed Volumes Processed

CalRes 2301 (A) CalRes 2301 (B) PSR2 Plus Cl (A) PSR2 Plus Cl (B) PFA694E Average Column Influent TOC

0 20,000 40,000 60,000 80,000 100,000 Bed Volumes Processed

Figure 10. Total Activated Carbon Results from Ion Exchange Column Effluent Figure 11. Per- and Poly-Fluoroalkyl Substances Removal Using Ion Exchange

Total PFAS Removal (%) 100%

98%

96%

94%

92%

90%

0 20,000 40,000 60,000 80,000 100,000 Bed Volumes Processed

carboxylic acid (PFOA, perfluoroheptanoic acid [PFHpA], perfluorohexanoic acid [PFHxA]) species.

Figure 8 and Figure 9 present individual PFAS removal as a function of BVs for the Evoqua UC1240LD and Calgon F-400 media, respectively. As is typical for adsorption column testing, shorter-chain PFAS broke through into column effluent sooner than longer-chain species, and sulfonic acid species were removed more effectively than carboxylic acid counterparts.

As described previously, the Calgon F-400 and Jacobi Aquasorb F23 performed the best with respect to PFAS removal. The F-400 performed best overall (the highest overall removal of the six PFAS), while the Aquasorb F23 demonstrated superior retention for PFOS, making it an ideal GAC if only PFOA and PFOS are of concern for removal. The PFOS and perfluorohexanesulfonic acid (PFHxS), the two PFAS that comprise a majority of the total PFAS concentration in the city’s water supply, broke through the columns slower than alternative PFAS.

Ion Exchange

The IX RSSCTs occurred in parallel to GAC media testing. Similarly to the GAC results, a suite of water quality parameters was monitored throughout bench-scale GAC testing. For brevity, only TOC and PFAS are presented herein.

Figure 10 presents TOC results from the IX columns. The same influent water for the GAC columns was used for the IX columns, with the average influent TOC level measured as 1.3 mg/L and ranging from 1.2 to 1.8 mg/L. The IX resins removed 0.2 to 0.3 mg/L of TOC (up to about 40k BVs) and had minimal removal by 100k BVs. This is likely due to the PFAS selectivity of IX resins.

The PFOS+PFOA figures are not presented since they were below detection limits in almost all IX column effluent samples, even after reaching 100,000 BVs in the columns.

Using RSSCT for IX evaluations is not as refined as RSSCT for GAC studies; therefore, it’s important to interpret the data with caution and remember that RSSCT is used for comparative purposes only, not for fullscale design, and piloting will determine the optimal PFAS treatment options.

Three types of resin were evaluated: S Calgon CalRes 2301 S Evoqua DOWEX PSR2 Plus S Purolite PurofinePFA694E

The Calgon and Evoqua resins were evaluated in duplicate columns. Figure 11 presents total PFAS removal as a function of BVs for the five IX columns. It’s important to note that the Y-axis was modified to show 90 to 100 percent removal, since total PFAS removal for each of the resins was relatively high.

In general, the Calgon and Evoqua resins outperformed the Purolite resin, although each of the resins provided greater PFAS removal, compared to GAC media. While IX resin often provides greater PFAS removal than GAC media and requires less-frequent change-outs, it’s important to note that IX resin is more costly than GAC media and provides limited removal of other constituents, such as TOC.

Conclusions and Next Steps

In 2018, PAC presented a good temporary option for the city because it was installed quickly and provided sufficient PFAS reduction; however, PAC has increased residuals loading and is not as robust as other available PFAS treatment options.

Both GAC and IX are good options for the city to consider for full-scale treatment. The top two best-performing GAC media and IX resin are currently being evaluated at the pilot scale. The IX resin provided better PFAS removal compared to GAC at the bench scale. While full-scale GAC would require morefrequent change-out compared to IX, GAC media is a lower-cost option and provides a secondary benefit of TOC adsorption that IX resin does not, due to resin PFAS selectivity. Short-chain PFAS started to break through GAC and IX columns prior to longchain PFAS as expected, based on industry findings to date. This may be of concern for the city and other utilities if short-chain PFAS are identified in water supplies as part of UCMR 5. Differences were identified between GAC in terms of total PFAS removal, with the Calgon carbon appearing to capture a wider range of PFAS and the Jacobi carbon appearing to target PFOS and PFOA. S