Graduation Year

2023

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Qiong Zhang, Ph.D.

Committee Member

Katherine Alfredo, Ph.D.

Committee Member

Norma Alcantar, Ph.D.

Committee Member

Sarina J. Ergas, Ph.D.

Committee Member

Shengqian Ma, Ph.D.

Keywords

Co-contaminants, Hybrid Adsorption System, Kinetics, Regeneration, Single and multicomponent isotherms

Abstract

Per- and polyfluoroalkyl substances (PFAS) are man-made environmental contaminants causing increasing global concern due to their adverse effect on environmental and human health. Conventional treatment methods are ineffective in removing short-chain PFAS because of their hydrophilicity and resistance to degradation. This study is to design an appropriate adsorption system to remove both long- and short-chain PFSA at environmentally relevant concentrations and conditions. Four primary research tasks were designed to evaluate the performance of a structurally-tunable and chemically-stable porous organic polymers (POPs) for PFAS removal under realistic environmental conditions, including the assessment of POPs’ performance without co-contaminants (Chapter 2), the assessment of their performance under the presence of co-contaminants (Chapter 3), the identification of appropriate regenerant concentration for POPs (Chapter 4), and the investigation of hybrid adsorption systems capable of successfully removing a full range of PFAS (Chapter 5).

This study investigated the short-chain PFAS removal efficiency of amine-functionalized POPs, methoxy group functionalized POP, and β-CD functionalized POP. These adsorbents were evaluated for their ability to remove short-chain PFAS at initial concentrations of approximately 400 ng/L. Amine-functionalized POP (POP-Py-4-NH2-CH3Cl) and methoxy group functionalized POP (POP-Py-4-OCH3) demonstrated impressive removal efficiency of 96.8% and 99.3% for PFBA at the dosage of 0.04 g/L. Furthermore, among the characteristics of POPs, it was observed that comonomer charge, ζ potential, and macro and mesopore volume exhibited a positive correlation with removal efficiency. This finding provides valuable insights into the material synthesis that can be optimized to enhance the adsorption of short-chain PFAS. Kinetic and isotherm studies demonstrated that POP-Py-4-NH2-CH3Cl and POP-Py-4-OCH3 exhibited high adsorption capacities for both long-chain and short-chain PFAS, and rapid kinetics leading to equilibrium times of less than 15 minutes.

pH in the range of 5 to 9 had minimal impact on the performance of POP-Py-4-NH2-CH3Cl and POP-Py-4-OCH3. Their PFAS removal efficiency remained consistent across the typical pH range in natural waters. Among the co-contaminants, inorganic anions such as Cl- had negligible interference with PFBA removal. However, the presence of organic matter (OM) and long-chain PFAS had a significant impact, leading to a decrease in the adsorption capacity of POPs. Despite this, POP-Py-4-NH2-CH3Cl and POP-Py-4-OCH3 demonstrated high removal efficiency in the presence of co-contaminants, indicating their potential as reliable adsorbents for the remediation of PFAS-contaminated water.

The combination of 10% NaCl and 30% methanol is the efficient and practical option for regenerating PFAS-loaded POP-Py-4-NH2-CH3Cl and POP-Py-4-OCH3. Additionally, the outstanding reusability of those two POPs was demonstrated with the selected regeneration condition after five adsorption and desorption cycles. Co-adsorbed OM on POP-Py-4-NH2-CH3Cl and POP-Py-4-OCH3 resulted in a slight decrease in regeneration efficiency by 6.5% and 8.7%, respectively. However, the findings highlight the excellent regeneration ability of those two POPs in complex water matrices.

Rapid small scale column tests (RSSCTs) revealed that short-chain PFAS exhibited faster breakthroughs than long-chain PFAS in both POP and granular activated carbon (GAC) columns. The hybrid adsorption system (GAC and POP column in series) exhibited an extended service life compared to the GAC stand-alone and POP stand-alone systems. The capital cost, operation & maintenance (O&M) cost, and annualized cost were found to be closely linked to the adsorbent cost. Considering the cost of producing POPs at 100 $/kg on a commercial scale, it was determined that they could provide a cost-effective solution for removing both long-chain and short-chain PFAS at environmentally relevant concentrations and under realistic conditions.

Overall, this research contributes to understanding PFAS removal using structurally-tunable and chemically-stable POPs under realistic environmental conditions. The characteristics of the designed POPs make them a highly promising and stable absorbent. It enables fast and effective removal of short-chain PFAS. The results also demonstrate the potential for POPs to be implemented in full-scale PFAS-contaminated water treatment systems.

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