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Production of renewable fuels and destruction of per- and polyfluoroalkyl substances (PFAS) from organic waste streams
Koehler, Andrew James
Koehler, Andrew James
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2025
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2026-11-11
Abstract
Increasing urbanization and industrialization have led to more waste within cities, creating new opportunities and challenges for wastewater treatment. One major opportunity is the potential to recover organic carbon and nutrients from aqueous waste streams to produce new fuels and chemicals, converting wastewater treatment plants into waste resource recovery facilities. Simultaneously, rising levels of per- and polyfluoroalkyl substances (PFAS) from domestic and industrial sources enter wastewater treatment plants, where a large portion of these toxic, persistent, and recalcitrant compounds (including PFOA and PFOS – two of the most regulated PFAS) sorb to wastewater residual solids (biosolids and sludge). This thesis describes two methods of valorizing organic carbon in wastewater, one of which simultaneously destroys PFAS.
In the first method, a wide variety of organic compounds found in wastewater are funneled into a single biopolymer using microbes. This biopolymer can be depolymerized to a single monomer (3-hydroxybutyric acid, 3HB), which can be upgraded to propylene. The work in chapter 2 highlights the vapor-phase dehydration and decarboxylation of 3HB over hydrothermally stable solid acid catalysts to form propylene, which can later be used to synthesize hydrocarbon fuels and industrial chemicals.
In the second method, PFAS is destroyed while energy and nutrients are recovered simultaneously from WWRSs by using hydrothermal liquefaction (HTL) in conjunction with a strong alkali (1–3 M NaOH) in a process known as hydrothermal alkaline treatment (HALT). The destruction of the most recalcitrant PFAS was found to depend on the ratio of applied NaOH to wt% of WWRS, with 20.10 molNaOH kg-1solids required to degrade PFSAs to non-detect levels within 1 h at 350°C; the extent of degradation increases with increasing reaction time and temperature. These results informed an open-source modeling platform (QSDsan) to characterize the economic and environmental sustainability of a treatment train employing HALT to upgrade WWRSs. In baseline HTL conditions without NaOH, the model predicts a sludge management cost of -54.80±63.37 $·tonne–1 which increases to 380.71±144.66 $·tonne–1 at conditions using HALT that destroy >99% of PFSAs. The impact of PFAS regulations and energy policy on total treatment cost is also described.
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