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NASF/AESF Foundation Research Project #120: Electrochemical Destruction of Perfluorooctanesulfonate in Electroplating Wastewater – 7th and 8th Quarter Report

By Brian Chaplin*
Department of Chemical Engineering
University of Illinois at Chicago
Chicago, Illinois, United States

Editor’s note: This NASF-AESF Foundation research project report covers the seventh and eighth quarters of project work (October 2021-March 2022) at the University of Illinois at Chicago. A printable PDF version of this report is available by clicking on HERE. A list of previous reports to date is provided at the end of this report.

Part 1 – 7e Quarterly report (October-December 2021)

Summary

Experiments were conducted to investigate 6:2 FTS oxidation, as it is a common replacement compound for PFOS in the electroplating industry. Experiments showed that FTS 6:2 was oxidized up to 77% in a single pass through Ti4Oseven reactive electrochemical membrane (REM), with a residence time of only 11 s. In addition, a sample of electroplating wastewater containing PFAS was obtained from an industrial partner. This solution will be tested for electrochemical oxidation of PFAS during the next quarter of the project. A new student has been hired to work on this project and started on January 18, 2022.

Part 2 – 8e Quarterly report (January-March 2022)

Summary

This quarter, a wastewater sample was obtained from an electroplating facility and experiments were conducted to study the oxidation of PFAS in both the wastewater sample and in synthetic solutions. Analysis of the sample determined that FTS 6:2 was the main PFAS detected at a concentration of 220 μg/L (~0.5 μM). The ionic content was mainly composed of NaCl and Na2SO4 salts, and the chemical oxygen demand (COD) of the sample was approximately 50 mg/L, which was attributed to other organic compounds in addition to PFAS.

Table 1 – General water quality parameters for the electroplating wastewater sample.

The waste water sample was treated with Ti4Oseven reactive electrochemical membrane (REM), with a residence time of about 11 sec. FTS 6:2 oxidation results are still awaiting LC-MS analysis. However, elimination of COD at potentials of 2.2, 2.9 and 3.6 VSHE was 10, 24, 83%, respectively. A synthetic solution with ionic content similar to real wastewater was prepared and spiked with 0.5 μM of 6:2 FTS. Again, PFAS analysis is still pending, but fluoride production in permeate samples increased as a function of potential and reached 4.9 μM (that’s to say., 75% defluorination) at a potential of 3.6 VSHE. Additionally, a synthetic sample with an ionic strength similar to that of wastewater was prepared but with a high FTS concentration of 6:2 (40 μM). This sample was used to represent a concentrate of PFAS from electroplating wastewater that may result from nanofiltration or foam fractionation. Results showed 66, 78 and 83% oxidation of 6:2 FTS at potentials of 2.2, 2.9 and 3.6 VSHE, respectively. Analysis of the product indicated the formation of short chain PFAS (that’s to say., PFHpA, PFHxA, PFPeA and PFBA) at concentrations below 1.35 μM. These results indicate that the concentration of PFAS in the wastewater may be a more effective treatment strategy and that the residence time in the REM must be increased to avoid the accumulation of short-chain PFAS byproducts.

Results

Electroplating wastewater was analyzed for PFAS and general water quality parameters. The total concentration of PFAS was 228 μg/L, consisting of 220 μg/L 6:2 FTS and low concentrations of 4:2 FTS (0.81 μg/L), PFHpA (0.38 μg/L), PFHxA (1.4 μg/L) and PFOS (2.2 μg/L). General water quality parameters are listed in Table 1. The results indicate that the ionic content consists mainly of NaCl and Na2SO4 salts, the solution pH = 7.35 and COD = 50 mg/L.

Figure 1 – Chemical oxygen demand (COD) of wastewater as a function of the potential in the REM system. Residence time ~ 11 sec.

The electrochemical oxidation of the wastewater sample was tested in the REM system. The flow was kept constant at 240 L/m2/ h, which corresponds to a residence time of about 11 seconds in the reactor. Applied potentials of 2.2, 2.9 and 3.6 VSHE have been tested and PFAS removal is still awaiting LC-MS analysis. The COD analysis of the wastewater is shown in Figure 1 and the results indicate that it decreased by 10%, 24% and 83% at potentials of 2.2, 2.9 and 3.6 V.SHE, respectively. State that REM was effective for bulk oxidation of organics in wastewater.

Figure 2 – Fluoride analysis for 0.5 μM 6:2 FTS oxidation in a synthetic wastewater sample as a function of potential. Residence time ~ 11 sec.

An additional experiment was also conducted with synthetic wastewater with 0.5 μM 6:2 FTS and similar ionic content as in Table 1, but without the bulk organics. PFAS analyzes are again pending LC-MS analysis. However, the fluoride analysis is shown in Figure 2. The results indicate that fluoride increases with potential and reaches a concentration of 4.9 mM, which corresponds to 75% defluorination of 6:2 FTS. This calculation was based on the fact that 1 mole of FTS 6:2 contains 13 moles of fluorine. Chlorate and perchlorate have also been monitored as they can form from the oxidation of chloride and pose undesirable health risks. Perchlorate was below the detection limit (~1 μg/L) and chlorate was detected at concentrations of 1.2, 23 and 95 mg/L at potentials of 2.2, 2.9 and 3.6 VSHE, respectively. Chlorate is currently unregulated, but the EPA has set a Health Reference Level (HRL) at 210 μg/L. Since chlorate concentrations are much higher than the HRL, the water may require additional treatment depending on discharge permits.

picture 3 – (a) Concentration of 6:2 FTS versus applied potential. Initial concentration of 6:2 FTS = 40 μM; (b) products of 6:2 FTS as a function of applied potential. The residence time is about 11 seconds.

An additional synthetic sample was prepared with an ionic strength similar to real wastewater, but with a high concentration of 6:2 FTS (that’s to say., 40 µM). This sample was used to represent a sample of concentrated PFAS that may be generated during nanofiltration, foam fractionation, or other separation method. Oxidation experiments indicated 66%, 78%, and 83% removal of 6:2 FTS at potentials of 2.2, 2.9, and 3.6 VSHE, respectively (Figure 3a). Product analysis indicated the formation of short chain PFAS (Figure 3b).

For example, the highest concentrations of PFHpA, PFHxA, PFPeA, and PFBA formed at a potential of 2.9 VSHE, with concentrations of 1.4, 1.0, 0.7, 0.06 μM, respectively. Concentrations of all these PFAS decreased to 3.6 VSHE at concentrations below 0.5 μM. These results indicate that the concentration of PFAS in wastewater can be a viable and effective treatment strategy and that the residence time in the REM must be increased to avoid the accumulation of short-chain PFAS byproducts.

Previous reports

1. Quarters 1 to 5 (April 2019-June 2021): Summary: NASF report in Products Finish; NASF Surface Technology White Papers, 86 (1), 19 (October 2021); Full article (with project introduction): http://short.pfonline.com/NASF21Oct1.

2. Quarter 6 (July-September 2021): Summary: NASF report in Products Finish; NASF Surface Technology White Papers, 86 (4), 19 (January 2022); Full article: http://short.pfonline.com/NASF22Jan2.

About the Author

Dr. Brian P. Chaplin is an associate professor in the Department of Chemical Engineering at the University of Illinois at Chicago. He holds a bachelor’s degree in civil engineering (1999) and a master’s degree (2003) in civil engineering from the University of Minnesota and a Ph.D. in Environmental Engineering (2007) from the University of Illinois at Urbana-Champaign.


* Dr. Brian Chaplin, Associate Professor
Department of Chemical Engineering
University of Illinois at Chicago
221 Chemical Engineering Building
810 S. Clinton Street
Chicago, IL 60607
Office: (312) 996-0288
Cell: (217) 369-5529
Email: [email protected]