| dc.description.abstract | Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic contaminants that pose long-term risks to groundwater, drinking water, agricultural soils, and aquatic environments. Their environmental behavior is controlled by a complex combination of molecular structure, soil properties, dissolved organic matter (DOM), and treatment-system chemistry. Because many PFAS are resistant to natural attenuation and conventional treatment, effective management requires both mechanistic understanding of their fate and transport in soil--water systems and the development of technologies capable of destructive removal. This dissertation investigates the environmental and engineered controls on PFAS mobility, retention, sorption, and degradation, with emphasis on the roles of dissolved organic matter and chitosan-modified biochar.
The first part of this work examines how dissolved organic matter controls PFAS transport in soil. Saturated column experiments were conducted using a clayey agricultural soil and a mixture of six PFAS, including short- and long-chain carboxylates and sulfonates. Four dissolved organic matter sources, including biosolids, Suwannee River natural organic matter, Pahokee peat, and Leonardite, were used to represent organic materials with distinct optical and chemical properties. Results showed that PFAS transport was strongly dependent on both PFAS molecular structure and dissolved organic matter composition. Long-chain PFAS, especially sulfonates, exhibited greater retardation, stronger tailing, and lower mass recovery than short-chain compounds. Dissolved organic matter altered PFAS mobility in source-dependent ways: some organic matter types enhanced retention and irreversible sequestration of long-chain PFAS, whereas more aromatic and humified dissolved organic matter reduced retention relative to DOM-free controls. Optical indicators, including SUVA254, humification index (HIX), and fluorescence index (FI), were useful predictors of PFAS transport behavior, demonstrating that DOM quality, rather than concentration alone, is a key control on PFAS leaching potential.
The second part of this dissertation evaluates engineered biochar as a platform for PFAS sorption and destructive treatment. Biochar was modified using iron oxide, zero-valent iron/chitosan, and chitosan to improve PFAS removal from water. Among the tested materials, chitosan-modified biochar showed the strongest PFAS sorption performance, largely due to favorable surface charge and enhanced interactions with anionic PFAS. When combined with UV/sulfite advanced reduction processes, chitosan-modified biochar significantly improved PFAS degradation and defluorination by concentrating PFAS near reactive radical species. This biochar-enabled advanced reduction system enhanced PFOS destruction and reduced the strong pH dependency commonly observed in UV/sulfite treatment.
The third part of this work extends the chitosan-modified biochar/UV-sulfite system to PFAS with different structures and to more environmentally realistic water chemistries. The system was tested for PFBS, PFHxS, PFOS, and PFOSA under varying ionic strength, nitrate, humic acid, and simulated groundwater conditions. Results demonstrated that degradation and defluorination were strongly influenced by PFAS chain length, headgroup chemistry, and matrix composition. Long-chain PFAS generally showed stronger adsorption and more effective degradation, while environmental constituents affected treatment efficiency by altering PFAS adsorption, radical availability, and interfacial reactions. Nitrate, in particular, promoted PFAS adsorption onto chitosan-modified biochar and indirectly enhanced defluorination under certain conditions, whereas natural organic matter had concentration-dependent effects.
Overall, this dissertation provides an integrated understanding of PFAS behavior across natural and engineered soil--water systems. It shows that interfacial processes govern both PFAS transport in soils and PFAS destruction in treatment systems. Dissolved organic matter can either mobilize or immobilize PFAS depending on its composition, while engineered biochar can be used to capture PFAS and promote destructive transformation. These findings improve the mechanistic basis for predicting PFAS leaching in amended soils and support the development of low-cost, biochar-enabled treatment strategies for PFAS-contaminated water. | en_US |
