Date of Award

1-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Yang Deng

Committee Member

Huan Feng

Committee Member

Jinshan Gao

Committee Member

Mengyan Li

Abstract

Per- and polyfluoroalkyl substances (PFAS) have been globally incorporated into various industrial and consumer products since the 1940s. However, concerns about PFAS have gradually grown because of their prevalence, mobility, persistence, bioaccumulation, and adverse impacts on human and environmental health. Unfortunately, traditional water treatment processes inefficiently remove PFAS. Therefore, there is an urgent research need to develop innovative, technically viable, and low cost-treatment processes for the removal of PFAS in water.

Among the established PFAS treatment technologies, ion-exchange (IX) has been extensively applied to drinking water treatment practices due to its adsorption capability and technology maturity. However, IX is highly cost-inefficient and environmentally unfriendly because of the expenses associated with off-site regeneration, no PFAS detoxification, and the production of harmful PFAS-containing regenerant waste required for careful disposal. In contrast, advanced reduction processes (ARPs) have demonstrated technical viability for PFAS degradation due to the powerful reducing potential of hydrated electron (eaq -) generated. Nevertheless, ARPs are restricted in realistic water treatment, particularly drinking water treatment, due to increased total dissolved solids in effluent, operational requirements in pH adjustment, and depletion of dissolved oxygen.

The primary objective of this dissertation is to advance the fundamental understanding of the interactions of eaq - and PFAS-laden IX resins, thereby providing a scientific basis for the development of an innovative on-site ARP-based IX resin regeneration method capable of recovering spent resins and degrading PFAS in drinking water treatment. Specifically, the design comprises repeated IX adsorption – ARP regeneration phases. In the first adsorption phase, trace PFAS in water is captured by IX resins until saturation. Subsequently, ARPs are launched to decompose PFAS laden on the resins for adsorption recovery before reuse. In the dissertation research, perfluorooctanoic acid (PFOA) was chosen as a model PFAS species owing to its prevalence in the aquatic environment, while ultraviolet (UV)/sulfite was selected as the representative ARP to generate eaq -. Five tasks were sequentially completed in this dissertation to achieve the primary objective.

In Task 1, a critical review of the destruction of aqueous PFAS with ARPs was conducted to retrospect the state-of-the-art knowledge on the emerging PFAS treatment technology and identify the critical knowledge gaps toward applications to drinking water treatment. In Task 2, bench-scale tests were performed to screen for a potentially durable resin to demonstrate the technical feasibility of eaq --driven ARPs for mitigation and degradation of PFAS laden on resins. Specifically, IRA67 resins were selected among eight commercially available resins for the subsequent dissertation studies because of their excellent PFOA adsorption capability and durable physical/chemical properties for consistently high PFOA. In Task 3, bench-scale tests were carried out to elucidate the interactions of eaq - and PFOA sorbed on the PFOA/NOM-laden IRA67 resins and assess the role of NOM co-sorbed on the IX resins in the proposed PFAS treatment approach. Results showed that PFOA, regardless of sorbed or aqueous states, could be effectively degraded by eaq -. However, UV/SO3 2- ARP treatment could not effectively decompose co-sorbed NOM to substantially recover the resin adsorption effectively. The buildup of NOM on the resins finally led to the loss of the resin capacity for capturing PFOA in water with the increasing cycle number. Therefore, two pretreatment strategies (i.e., coagulation and UV/hydrogen peroxide (H2O2)-based advanced oxidation process (AOP)) were assessed in Task 4 to alleviate NOM loading on PFOA/NOM-laden IRA67 and to evaluate the effect of pH on desorption of co-sorbed NOM during the IRA67 regeneration processes, respectively. Moreover, the optimized cyclic adsorption-regeneration tests combined with the NOM mitigation strategies were evaluated for the repeated removal of PFOA in water. Results showed that alum coagulation at the optimized operational conditions (i.e., alum 60.0 mg/L; pH 6.0) significantly alleviated the NOM loading on IRA67, but the UV/H2O2-based AOP could not further reduce the PFOA loading on IRA67. The continuous adsorption of PFOA by IRA67 in the cyclic adsorption-regeneration process was ascribed to NOM desorption at pH 10.0 during the ARP regeneration process to release more occupied sites on IRA67. Therefore, the UV/SO3 2- process operated at an alkaline condition, if jointly used with alum coagulation as a pretreatment step, can enable a promising on-site regeneration process for the PFOA/NOM-laden IRA67 in drinking water. The information will be input to Task 5 in which the implications of the proposed ARP-based resin regeneration technologies were discussed in terms of economic, environmental, and social aspects, major conclusions were summarized, and future research directions were identified. The dissertation builds a basis for an innovative ARP-enabled on-site IX regeneration approach to PFAS pollution in drinking water treatment. The resin adsorption capacity can be substantially recovered, accompanied by the PFAS degradation and the production of a small volume of easily managed regenerant waste.

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