Gao, Ruilian (2020-11). Kinetic Model of Perfluoroalkyl Substances Removal from Environmental Matrices Via Electron Beam Irradiation. Master's Thesis.
Thesis
Per- and polyfluorylalkyl substances (PFASs) products, including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), were widely produced in the industry and commercial products. They were detected in natural waters and soil matrix. The high bond energy of carbon-fluorine bond in PFASs lead the high difficulty of breakdown. Previous study proved the toxicity and bioaccumulation of PFASs. A cost-effective and efficient way to decompose PFASs in water and soil matrix has to be investigated. Electron beam with high energy after an accelerator can generate a large number of reactive species in water like hydrated electron (eaq-), hydroxyl radical (oOH), and hydrogen radical (Ho). These reducing and oxidizing agents play an important role to break down the carbon-fluorine bond based on the previous studies. 10 MeV, 15kW electron beam was used to individually treat PFOA, PFOS, and PFHpA solution at 100 ug/L in HPLC water, groundwater samples from Pennsylvania, soil samples from Michigan. The effect of different pH values, concentrations of bicarbonate, nitrate, and fulvic acid were studied to investigate during PFHpA degradation. Preliminary results show that > 14.61% PFOA removal was observed at pH 13.0 with 75 kGy eBeam, and PFOS has the similar decomposition efficiency at the same experiment conditions. The experiment shows that low dose irradiation could not fully removal of PFASs in water. For PFHpA, nitrate ion, bicarbonate, and fulvic acid at pH 13.0 in spiked water sample will not have negative effect on breakdown where the removal percentage is 100%. Higher pH had a positive effect on spiked PFHpA sample. The irradiation experiments of investigation-derived waste (IDW) samples without any pH adjustment with high doses from 0 to 2000 kGy showed the increasing degradation percentage of PFASs. For Pennsylvania water sample, the breakdown percentage was about 88% at 2000 kGy. For PFOS was rapidly degraded until 1000 kGy, while PFHpA firstly increased before 500 kGy and then breakdown until 2000 kGy. Further, kinetic model was proposed to investigate the possible pathway of PFAS breakdown. All the concentration or mass of degradation products and PFOA, PFOS satisfied the pseudo first kinetic order. At the PA-WATER field sample, PFOA and PFOS was decomposed with the rate constant of 1.21 x 10-3 kGy-1s-1, 3.3 x 10-4 kGy-1s-1 respectively. The reaction kinetics of short chain PFAS (PFHpA) was < 2.16 x 10-3 kGy-1s-1, almost one orders magnitude lager than other short chain PFAS. This study proves the high efficiency of eBeam as a promising technology that can be performed to remediate PFASs and other co-contaminants in aqueous and solid environmental matrices such as groundwater and soils.
