Matching Items (3)
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- All Subjects: PFAS
- Creators: Conroy-Ben, Otakuye
- Creators: Garcia-Segura, Sergi
Description
Hydrophobic ionizable organic compounds (HIOCs) like per- and polyfluoroalkyl substances (PFAS), certain pharmaceuticals, and surfactants have been detected in groundwater, wastewater, and drinking water. Anion exchange resin treatment is an effective process for removal of anionic contaminants from water. Spent anion exchange resins are conventionally regenerated with high alcohol by volume (ABV) methanol in solution with brine. While effective for regeneration of resins saturated with inorganic anions such as sulfate, nitrate, and perchlorate, HIOCs prove more resistant to regeneration. This research investigated the efficacy of using novel cosolvent solutions with brine to regenerate resins saturated with organic carboxylate and sulfonate anions to understand the effects cosolvent properties have on regenerative ability. Experiments were conducted on six PFAS compounds to evaluate trends in regeneration for three alcohols. For all PFAS species, equivalent ABV and brine solutions showed greatest regeneration with 1-propanol over ethanol and methanol. Experiments with the pharmaceutical sodium diclofenac were conducted showing similar regeneration of 75% methanol and 25% 1-propanol for equivalent salt concentrations and higher regeneration with 1-propanol than ethanol and methanol for equivalent ABV. A series of experiments with surfactant dodecylbenzene sulfonate determined that the key parameters to determine regeneration of the resin for an alcohol cosolvent solution were cosolvent volume fraction, molar mass, Kow value, solution ionic strength, and dielectric constant. Individual assessments on the cost-effectiveness, flammability, and sustainability of cosolvent solutions point to possible future experiments and opportunities for recycled distillery waste streams as regenerative solutions for anion exchange resin.
ContributorsGraham, Cole David (Author) / Boyer, Treavor H (Thesis advisor) / Conroy-Ben, Otakuye (Committee member) / Garcia Segura, Sergio (Committee member) / Arizona State University (Publisher)
Created2022
Description
Although anion exchange resins (AERs) have been implemented for a wide range of aqueous contaminants including notorious perfluoroalkyl acids (PFAAs) that are of human health concern, the potential benefits and underlying chemistry of weak-base (WB) AERs are overlooked. To fill these key gaps in the literature, this research evaluated the removal and regeneration efficiency of WB-AER (IRA 67 and IRA 96) with strong-base (SB) AER as the baseline. Batch equilibrium tests were first conducted for the removal of nitrate, sulfate, 3-phenylpropionic acid, and six legacy PFAAs with contrasting properties at different solution pH using polyacrylic and polystyrene chloride-form AERs. In ambient (pH 7) and acidic (pH 4) solutions, the polymer composition was the controlling factor followed by the length of alkyl chain of the resin while AER basicity did not influence the selectivity for the selected contaminants. WB resin had higher capacity than SB analogs based on quantitative analysis using isotherm model parameters. Batch and column adsorption experiments showed significantly greater removal of PFAAs by polystyrene than polyacrylic AERs regardless of resin basicity, with the order of decreasing polyacrylic resin selectivity of PFOS >> PFHxS ≈ PFOA > PFBS > PFHxA ≈ PFBA. The removal performance of WB-AER was reversible, declining drastically at basic conditions and gradually regained once below the pKa of the resin due to the pH-dependent nature of amine groups. This was not the case for IRA 96 (i.e., polystyrene) which exhibited high removal of PFAAs irrelevant of pH because of the nonpolar character of polystyrene matrix. The non-hydrophobic IRA 67 (i.e., polyacrylic) had a satisfactory regeneration using non-toxic salt-only solutions comprising 1% NaOH and 0.5% NaOH + 0.5% NaCl, while IRA 96 was only amenable to brine/methanol regeneration. Important caveats on the validity of isotherm modeling in batch adsorption tests were discussed. Results for batch and column experiments using chloride-form and free-base form WB-AER, respectively, provide insights for industrial applications.
ContributorsKassar, Christian (Author) / Boyer, Treavor H. (Thesis advisor) / Westerhoff, Paul K. (Committee member) / Conroy-Ben, Otakuye (Committee member) / Arizona State University (Publisher)
Created2022
Description
Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals used for a wide variety of products and industrial processes, including being an essential class of chemicals in the fabrication of semiconductors. Proven concerns related to bioaccumulation and toxicity across multiple species have resulted in health advisory and regulatory initiatives for PFAS in drinking and wastewaters. Among impacted users of PFAS, the semiconductor industry is in urgent need of technologies to remove PFAS from water. Specifically, they prefer technologies capable of mineralizing PFAS into inorganic fluoride (F-). The goal of this thesis is to compare the effectiveness of photo- versus electrocatalytic treatment in benchtop reactor systems PFAS in industrial wastewater before selecting one technology to investigate comprehensively. First, a model wastewater was developed based upon semiconductor samples to represent water matrices near where PFAS are used and the aggregate Fab effluent, which were then used in batch catalytic experiments. Second, batch experiments with homogenous photocatalysis (UV/SO32-) were found to be more energy-intensive than heterogeneous catalysis using boron-doped diamond (BDD) electrodes, and the latter approach was then studied in-depth.
During electrocatalysis, longer chain PFAS (C8; PFOA & PFOS) were observed to degrade faster than C6 and C4 PFAS. This study is the first to report near-complete defluorination of not only C8- and C6- PFAS, but also C4-PFAS, in model wastewaters using BDD electrocatalysis, and the first to report such degradation in real Fab wastewater effluents. Based upon differences in PFAS degradation rates observed in single-solute systems containing only C4 PFAS versus multi-solute systems including C4, C6, and C8 PFAS, it was concluded that the surfactant properties of the longer-chain PFAS created surface films on the BDD electrode surface which synergistically enhanced removal of shorter-chain PFAS. The results from batch experiments that serve as the basis of this thesis will be used to assess the chemical byproducts and their associated bioaccumulation and toxicity. This thesis was aimed at developing an efficient method for the degradation of perfluoroalkyl substances from industrial process waters at realistic concentrations.
ContributorsNienhauser, Alec Brockway (Author) / Westerhoff, Paul (Thesis advisor) / Garcia-Segura, Sergi (Committee member) / Thomas, Marylaura (Committee member) / Green, Matthew (Committee member) / Arizona State University (Publisher)
Created2021