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Evaluation and implementation of adsorption technologies for the treatment of per and polyfluoroalkyl substances
Murray, Conner Coats
Murray, Conner Coats
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2021
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2022-10-14
Abstract
Contamination of water resources by per- and polyfluoroalkyl substances (PFAS(s)) has recently emerged as a significant problem worldwide. Applications of PFASs in household products, electronics, and firefighting foams has created substantial environmental remediation challenges in the treatment of these highly stable chemicals. While many conventional and advanced treatment approaches are ineffective for PFAS removal, adsorption technologies represent an effective and commercial ready treatment alternative. Although adsorbents such as granular activated carbon (GAC) and ion exchange resin (IX) are frequently applied in the treatment of PFAS contaminated waters, there is still an insufficient understanding related to the factors that influence short and long chain PFAS removal performance and the cost effectiveness of these treatment strategies. Novel adsorption technologies have emerged as potential replacements for GAC and IX but currently lack a comprehensive evaluation of their PFAS adsorptive potential in a variety of contaminated matrices. Studies within this thesis further the understanding of current and novel adsorbents and the adsorbate properties which impact PFAS adsorption performance in continuous flow treatment applications.
GAC and IX for PFAS adsorption was evaluated with columns in series to determine the impact of empty bed contact time (EBCT) and mass transfer zone (MTZ) length on the adsorption of long and short chain PFASs. Long chain PFAS adsorption with GAC required only 6 minutes of EBCT while short chain adsorption was more challenging with a longer MTZ necessitating at least 9 minutes of EBCT. Treatment with IX had similar chain length dependence with longer EBCT (3 minutes) required for short chain PFAS removal. Treatment capacity calculations for GAC and IX also contributed to a cost comparison which deemed IX as a more cost effective adsorbent for meeting short and long chain treatment objectives.
Further evaluation of the PFAS treatment capacity of GAC and IX was conducted with five distinct PFAS contaminated waters using a small-scale column system. PFAS adsorption comparison with GAC and IX was paralleled by the assessment of a novel surface modified clay (SMC) adsorbent. SMC adsorption of short and long chain PFAS was generally superior to GAC yet inferior to the removal capacity of IX. Application of the Thomas model to the observed breakthrough data yielded a calculation of the equilibrium adsorption capacity for each adsorbent in the removal of PFASs from each contaminated water type. The adsorption capacity of each adsorbent was found to be positively correlated to influent PFAS concentration while the concentration of background water quality constituents diminished adsorption effectiveness. Assessment of treatment feasibility for GAC, IX, and SMC adsorption in complex waters also featured an evaluation of adsorbent cost to inform treatment selection. The nearly three-fold discount in unit adsorbent cost of SMC relative to IX was sufficient qualification for SMC being the most cost effective adsorbent evaluated despite a lower PFAS adsorption capacity.
Investigation of novel adsorbents for PFAS removal was expanded to examine the PFAS adsorption capacity of super fine powdered activated carbon (SPAC) applied in a coupled ceramic microfiltration system. Adsorption performance of SPAC was found to be more than 480 times better than GAC in the treatment of perfluoroalkyl acids and polyfluorinated precursors in highly contaminated water from a firefighting training area. Complete separation of SPAC by the ceramic microfiltration system in multiday experiments validated the commercial potential of this technology for the treatment of highly contaminated water types. Additional evaluation of novel adsorbents with a focus on the development of disposal, costing, and breakthrough modeling practices are suggested to support PFAS remediation moving forward.
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