Date of Award

4-2025

Degree Name

Doctor of Philosophy

Department

Geological and Environmental Sciences

First Advisor

Donald Reeves, Ph.D.

Second Advisor

Daniel Cassidy, Ph.D.

Third Advisor

Neil Danielson, Ph.D.

Keywords

Foam drainage, foam fractionation, PFAS treatment, skimmer, surfactant removal

Abstract

Observed trends in municipal solid waste landfills reveal a distinct disparity between per- and polyfluorinated alkyl substances (PFAS) composition entering in waste, mostly as diPAP and FTOH, and leaching out as FTCA and PFCA. These patterns are elucidated by compiling PFAS compositions in paper, textiles, and carpet, with known precursor transformations that generate FTCA and PFCA in leachate. Landfill leachate is commonly discharged to wastewater treatment plants (WWTP), which are ineffective at degrading PFAS and only serve as key conduits and discharge points for PFAS to the environment. Foam fractionation has been identified as a promising technology for concentrating and capturing PFAS in waste streams such as landfill leachate but has yet to be demonstrated at the full WWTP scale (108 L/D). In this work, PFAS enrichment in foam was investigated for the first time at a cascade within a WWTP. A novel sampling device was utilized to allow spatial and temporal heterogeneity in PFAS concentrations and liquid content to be characterized. Concentrations of 8 PFAS compounds were normalized to liquid content and fit to a power law model revealing strong correlation (R2 = 0.91) between drainage induced enrichment and PFAS molar volume. Short chain PFAS such as PFBA exhibited minor to no enrichment factors in foam with factors of 0.24-5.9 compared to effluent concentrations across a broad range of foam liquid content (0.28-6.24%), while long chain compounds such as PFOS became highly enriched with factors of 295-143,000. A conceptual model is proposed to explain higher than expected enrichment of more surface-active PFAS relative to liquid content, which combines continuous partitioning of PFAS to air bubbles during foam formation with additional partitioning during non-linear drainage and foam collapse, both controlled by the affinity of PFAS for the air-water interface. Scoping calculations suggest the majority of PFOS and other long chain PFAS may be removed if foam is continuously collected, which could potentially reduce waste volume below economic barriers for current destructive technologies. Three foam collection methods for removal of PFAS —passive overflow, mesh skimmer, and mesh-belt skimmer—were iteratively designed and evaluated for continuous collection of foam forming at a WWTP cascade. Surface tension, PFAS concentrations and foamate collection rates were measured to assess their performance. Foam collection using a novel mesh skimmer and mesh-belt skimmer substantially increased PFAS enrichment over that of the in situ foam (up to >65 times more enriched), as the mesh facilitated drainage of PFAS-depleted liquid during collection. When scaled up, enhanced enrichment and scalable foam collection with mesh-belt skimming may remove and concentrate most long-chain PFAS (>90%) in under 270,000 L/d of foamate (i.e., 0.26% of the wastewater volume). For comparison, an estimated 900,000 L/d of foamate is needed with the passive overflow method to achieve 90% PFOS removal, and would only capture 20% PFOA and 22% PFHxS. Reducing the volume proportionally reduces follow-on treatment costs for the final collected foamate. While a pilot scale study is required to accurately assess removal, the advantages provided by the mesh-belt skimmer suggest feasible foam collection for PFAS removal at the full WWTP scale.

Access Setting

Dissertation-Open Access

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