Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Hyeok Choi

Abstract

In recent years, per- and polyfluoroalkyl substances (PFAS) have gained notoriety due to environmental and health concerns. These molecules are chemically stable which contributes to their persistence in biological systems and their increased detections in surface waters. Treatment of highly persistent PFAS has been a challenging but significant task. The most practical technique for removal of PFAS is through adsorption onto granular activated carbon (GAC) or other novel materials. Meanwhile, PFAS are resistant to simple oxidation, and although decomposition of specific PFAS has been reported through advanced oxidation technologies, often energy-intense technologies capable of generating electrons such as ultraviolet radiation, microwave, or high temperatures are required when coupled with an oxidant to generate highly reactive radical species. The use of such technologies increases the cost and lowers its practical applicability. Hence, in an effort to develop a practical treatment technology, an adsorption-based decomposition technology was envisioned. The high surface area of GAC poses a unique opportunity of housing reactive materials inside the pores. To achieve this, zero valent iron (ZVI), previously demonstrated to reductively delahogenate other persistent pollutants, was incorporated into the pores of the GAC, so called reactive activated carbon (RAC). Additionally, to generate highly oxidizing radical species persulfate (PS) was injected. Hence, once PFAS are encapsulated inside the pores, a combination of both reductive and oxidative species is present in close proximity to decompose the much recalcitrant PFAS. To demonstrate its effectiveness and understand its behavior, 6 PFAS of different functional groups and carbon chain lengths were investigated. An adsorption isotherm was first developed to test the affinity of the selected GAC. Then, the effects of reaction temperature, injection of PS, and presence of soil on removal of PFAS in water by RAC were evaluated. Results showed that RAC conjugated with PS at 60 ℃ exhibited decomposition of PFAS, exclusively all 3 carboxylic PFAS tested, obviously producing various identifiable short chain PFAS. Carboxylic PFAS were removed via physical adsorption combined with chemical decomposition while sulfonic PFAS were removed via solely adsorption mechanism. The presence of soil particles did not greatly affect the overall removal of PFAS. Carbon mass balance suggested that chemical oxidation by radical mechanisms mutually influences, in a complex manner, PFAS adsorption to GAC, ZVI and its iron derivatives, and soil particles. Nonetheless, all tested 6 PFAS were removed significantly. If successfully developed, the adsorption-mediated decomposition strategy may work for treatment of complex media containing PFAS and co-contaminants under different environmental settings. Future studies are required, to ensure the decomposition of PFAS exclusively inside the pores of RAC, additionally the synthesis of RAC containing different types of reactive metals and oxidants should be investigated. Pilot scale studies should also be conducted to simulate treatment beds and evaluate the effectiveness of the system.

Keywords

Per- and polyfluoroalkyl substances (PFAS), Reactive activated carbon (RAC), Persulfate, Iron, Advanced oxidation, Adsorption, Decomposition

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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