NASF/AESF Foundation Research Project #122: Electrochemical Approaches to Treatment of PFAS in Plating Wastewater – 4th Quarterly Report

from
Qingguo (Jack) Huang* and Yuqing Ji
University of Agricultural and Environmental Sciences
University of Georgia
Griffin, GA, USA

Editor’s note: For 2021, the NASF-AESF Foundation Research Board has selected a project to address the issue of PFAS and related chemicals in plating effluent streams. This report covers the fourth working quarter (October to December 2021). A printable PDF version of this report is available by clicking HERE.

introduction

This project started in January 2021 with the aim of developing applicable electrochemical approaches to remove per- and polyfluoroalkyl substances (PFASs) present in electroplating effluents, including electro-oxidation (EO) and electro-coagulation (EC). This project includes three research tasks designed to study the EC, EO and EC-EO treatment train respectively and to investigate the three hypotheses specified below:

1) EC produces amorphous metal hydroxide flakes, which can effectively adsorb PFAS in electroplating effluent, which through appropriate treatment can release PFAS into a concentrated solution.

2) EO enabled by a Magnéli phase Ti4O7 Anode can be used to effectively destroy PFAS in electroplating effluent.

3) The electrochemical treatment train composed of EC and EO by Ti4O7 -Anode can remove and degrade PFASs in the plating effluent more efficiently than either process operated individually.

Results reported in previous reports of this project demonstrated the feasibility of a novel treatment train that combines electrocoagulation (EC) with electro-oxidation (EO) to remove and degrade per- and polyfluoroalkyl substances (PFASs) from plating effluents. Electrocoagulation with a zinc anode can effectively remove PFAS from water, especially the long-chain PFAS (C7 – C10), which are present in the electroplating waste water, through accumulation on the flakes or in the foams produced during the EC. Both the flocs and the foams can be acid dissolved to recover and concentrate the PFASs in controlled volumes. The concentrated PFASs in the acid solutions were efficiently destroyed using an EO treatment with a Ti4O7 anode at 10mA/cm2, and no additional electrolyte was needed for the flakes dissolved in solution. This electrochemical based EC-EO treatment train is likely to be able to economically separate, concentrate and destroy PFASs in plating effluents.

This report describes our continued efforts in Task 3. First, we calculated the energy consumption of the EO treatment process in terms of EE/O, which is defined as the electrical energy required to increase the concentration of a pollutant by an order of magnitude (kWh) to reduce / m3).1 Second, we evaluated means of removing residual zinc ions that may be present after EO treatment of the acid-dissolved zinc flake solution.

Experimental

The calculation of EE/O was based on the results of the previously reported EO treatment experiment shown in Figure 2 in Figure 3approx Report.2 In this experiment, three different concentrated solutions prepared by the electrocoagulation (EC) method were subjected to electro-oxidation (EO) treatment using Magnéli phase Ti4O7 anodes at a current density of 10 mA/cm2. Solution I was the acid-dissolved solution of PFASs-loaded flocs generated using a low current density condition after 120 min (0.3 mA/cm).2, 0.005 μM of each 10 PFASs). Solution II was the flake solution loaded with acid-dissolved PFASs obtained by EC treatment under the high current density condition after 60 min (5 mA/cm²).2, 0.5 μM of each 10 PFASs). The foam collected during this EC process was supplemented with 20 mM Na2SO4 to a final volume of 10 ml as solution III.

An experiment was conducted to evaluate the methods of removing zinc ions from the solution produced by acid dissolution of the zinc hydroxide flakes produced during the EC process. In particular, removal of zinc ions has been achieved by precipitation with the addition of Na2S or Na2CO3. In this experiment, EC was first performed in 20 mM Na2SO4 Solution with PFASs at 0.3 mA/cm2 for 120 min or at 5 mA/cm2 for 60 min. The entire solution, including flakes, was then collected and filtered through a 0.22 µm acetate membrane filter. The EC flakes from both current density conditions were then collected and dissolved in 10 mL of 4.0 MH2SO4or N/A2S or Na2CO3 was then added to the solution in varying doses. The concentration of Zn2+ in the solution was determined with an ICP-MS (Perkin Elmer Elan 9000 inductively coupled plasma, equipped with a mass spectrometer)3 with a detection limit of 0.05 mg/L.

results and discussion

The EE/O (kWh/m3) of PFAS degradation in the three solutions described above was calculated by Equation 1,1

$EE/O=\frac{U_{cell}I}{V}t_{90%}$ (1)

Where ucell is the average cell voltage during EO treatment (V), I is the applied current (A), v is the volume of the reaction solution (L). t90% is the time (hrs) for 90% PFAS removal calculated using Equation 2:

$t_{90%}=ln\left ( \frac{C}{C_{0}} \right )/60k$ (2)

Where C/C0 is 10% and k (min-1) is the pseudo-first-order rate constant for the degradation of various PFAS in the three solutions obtained by fitting the PFAS degradation data shown in Fig. 1 of 3approx Report,2 to the pseudo-first-order rate model listed in Table 1.

The calculated EE/O values ​​of PFAS degradation in concentrated solution are presented in Table 2. The EE/O varies between 0.34 and 15.7 kWh/m3 for different PFAS in different solutions. It appears that the EE/O was lower for the long-chain PFAS, eg., PFNA, PFOA, PFOS, than the shorter, eg., PFBS and PFHxA. It is striking that the EE/O for the PFAS that are often present in electroplating waste water is particularly low, for example it was 0.66 (kWh/m3) for 6:2 FTS, 0.55 (kWh/m3) for PFOS and 0.95 (kWh/m3) for PFOA in solution I. Such EE/O values ​​are considered favorable for wastewater treatment applications.

The result of the experiment evaluating the methods of removing zinc ions from the solution by precipitation with the addition of Na2S or Na2CO3 is shown in FIG. It can be seen that the zinc concentration remaining in solution decreased dramatically when Na was added2S or Na2CO3 increased due to the precipitation of ZnS or ZnCO3. Almost all dissolved Zn2+ precipitated when sufficient salts had been added. This demonstrates that chemical precipitation can be used as an effective means of removing residual zinc in the final effluent of the proposed EC-EO treatment train.

Table 1 – The pseudo-first-order rate constant (min-1) of PFAS in concentrated solution in the EO process.

Table 2 – EE/O (kWh/m3) for the degradation of PFAS in concentrated solution during the EO process.

illustration 1 – Concentration of zinc ions in the solution at different current densities and with Na2S or Na2CO3 added in different doses.

references

1. K Yang, H Lin, S Liang, R Xie, S Lv, J Niu, J Chen, and Y Hu, “A porous Ti/SnO reactive electrochemical filter system with excellent penetration flux2–Sb filter for efficient removal of pollutants from the water”, RSC Adv., 8th (25), 13933-13944 (2018).

2. Q. Huang, “NASF/AESF Foundation Research Project #122: Electrochemical Approaches to Treatment of PFAS in Plating Wastewater – 3approx quarterly report,” NASF Surface Technology White Papers, 86 (6), 11-14 (2022); http://short.pfonline.com/NASF21Dec2.

3. Shu Y, Zheng N, Zheng A, Guo T, Yu Y, and Wang J. “Intracellular zinc quantification by fluorescence imaging using a FRET system, Anal. chem., 91 (6), 4157-4163 (2019).

Reports of past projects

1. Introduction to Project R-122: Summary: NASF report in Products finishing; NASF Surface Technology White Papers, 85 (6), 13 (March 2021); Full paper: http://short.pfonline.com/NASF21Mar1.

2nd Quarter 1 (January-March 2021): Summary: NASF report in Products finishing; NASF Surface Technology White Papers, 85 (12), 13 (September 2021); Full paper: http://short.pfonline.com/NASF21Sep1.

3rd Quarter 2 (April-June 2021): Summary: NASF report in Products finishing; NASF Surface Technology White Papers, 86 (3), 18 (December 2021); Full paper: http://short.pfonline.com/NASF21Dec2.

4th Quarter 3 (July-September 2021): Summary: NASF report in Products finishing; NASF Surface Technology White Papers, 86 (6), 16 (March 2022); Full paper: http://short.pfonline.com/NASF22Mar2.

Qingguo (Jack) Huang is Professor in the Department of Crop and Soil Sciences, University of Georgia, Griffin Campus. He holds a BS in Environmental Sciences (1990) and a Ph.D. in chemistry (1995) from Nanjing University, China and a Ph.D. in Environmental Engineering from the University of Michigan, Ann Arbor, Michigan. The research interest of Dr. Huang focuses on catalysis involved in the environmental conversion of organic pollutants and the development of catalysis-based technologies for pollution control, environmental remediation and management. His laboratory has been actively involved in several cutting-edge research topics:

Enzyme-based technology for water/wastewater treatment and soil remediation
Electrochemical and reactive electrochemical membrane processes in wastewater treatment
Catalysis in biofuel production and agroecosystem management
Environmental behavior and destructive treatment methods of PFASs
Environmental use and impact of nanomaterials

He has published over 160 peer-reviewed journal articles, five book chapters, and four patents and three patent applications. He has taught three courses at the University of Georgia: Introduction to Water Quality, Environmental Measurement, and Advanced Instrumental Analysis in Environmental Studies.

* Contact details of the principal investigator (PI):

Qingguo Huang, Ph.D, Professor, Department of Plant and Soil Sciences
University of Georgia
1109 attempt St.
Griffin, GA 30215, USA.

Phone: (770) 229-3302 Fax: (770) 412-4734
Email: [email protected]