ORCID

0000-0002-2868-2643

Date of Award

Fall 2024

Language

English

Embargo Period

12-11-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Environmental and Sustainable Engineering

Program

Environmental and Sustainable Engineering

First Advisor

Kyoung-Yeol Kim

Second Advisor

Xiaobo Xue Romeiko

Committee Members

Rixiang Huang; Yaoze Liu

Subject Categories

Environmental Engineering

Abstract

Electrocoagulation (EC) with a zinc anode demonstrated promising results to remove perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from an aqueous solution. However, the energy requirement for EC is usually very high due to water electrolysis or aeration. The second chapter of this dissertation aims to reduce energy consumption using an air-cathode in EC (ACEC) to supply oxygen electron acceptor without aeration for attenuating PFOA/PFOS in this new configuration. For the high PFOA concentration (0.25 mM), ACEC with 45 min of the reaction time exhibited an excellent PFOA removal (99.8 ± 0.3% removal) comparable to an EC with aeration (EC-aeration, 100% removal) while achieving much less energy consumption (0.14 kWh/m3). For the low PFOA concentration (0.1μM), only 41.1 ± 11.6% was removed by the ACEC due to the low concentration gradient for adsorption. EC- aeration achieved higher PFOA removal (81.9 ± 15.1%) for the low PFOA concentration, possibly because air bubbles floated PFOA to the water surface, thereby concentrating PFOA. The PFOS removals in the ACEC and EC-aeration (76.4–88.5%) at the high concentration (0.25 mM) were lower than PFOA due tentatively to its micelle formation. However, PFOS was removed better than PFOA at the low concentration (0.1μM) due to its higher hydrophobicity.

Besides hydrophobic interactions between PFOA/PFOS and zinc hydroxide flocs, aeration is another crucial factor determining PFOA/PFOS removal in EC. The third chapter of this dissertation examined how aeration (in terms of bubble sizes and flow rates) could impact PFOA/PFOS removal in EC. Both bubble sizes (coarse vs. fine) and airflow rates (7.9, 9.4, and 11.0 mL/sec) were critical for PFOA removal and zinc hydroxide floc generation. EC aerated with fine bubbles had 14-21% higher PFOA removal efficiency than EC aerated with coarse bubbles. PFOA removal by EC with a high airflow (11.0 mL/sec) was 19% higher than EC with a medium airflow (9.4 mL/sec), or 31-37% higher than EC with a low airflow (7.9 mL/sec). These results indicate that fine bubbles and high airflow rates are more beneficial for PFOA removal, likely due to a greater air-water contact area and turbulence. The EC with coarse bubbles produced zinc hydroxide flocs with 29-34% greater Brunauer–Emmett–Teller (BET) surface area and 18% greater mass. However, the BET surface area and mass of the flocs were not critical for PFOA removal. The impacts of aeration on PFOS removal in EC were not significant.

The fourth chapter of this dissertation evaluates the life cycle environmental impacts and financial costs of PFOA and PFOS removal through EC. Zinc electrode consumption emerges as the primary contributor, accounting for 42% to 97% of both life cycle impacts and financial costs. Compared to granular activated carbon (GAC)-based PFAS removal, EC shows 99.6% lower fossil fuel depletion at mg/L initial PFOA/PFOS concentrations, but a 4.3-fold increase in fossil fuel depletion at μg/L levels. The life cycle impacts and costs of EC remain relatively consistent across varying PFOA/PFOS concentrations; even with a 5000-fold difference in initial concentrations, the fluctuations in fossil fuel depletion and financial costs do not exceed 70%.

License

This work is licensed under the University at Albany Standard Author Agreement.

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