University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
The overall goal of this dissertation was to evaluate the removal of organic micropollutants by high-pressure membranes (both commercial and in-house varieties) and assess how interfacial polymerization (IP) reaction conditions employed in high-pressure membrane fabrication affect membrane performance. In support of this goal, the following specific objectives were pursued: (i) evaluate the effects of zeolite thin-film nanocomposite (TFN) membrane fabrication variations on the removal of a subset of organic micropollutants commonly found in wastewater effluent; (ii) elucidate whether changes in membrane fabrication parameters yield the same effects on thin-film composite (TFC) and zeolite TFN membrane performance; (iii) assess whether IP in TFC membrane fabrication is inherently self-limiting, and evaluate the effects of constant m-phenylenediamine (MPD) supply during IP in the modification of existing, and fabrication of new, TFC membranes; and (iv) evaluate the impacts of membrane type, IP reaction modifications, and per-and polyfluoroalkyl substances (PFAS) physicochemical characteristics on PFAS removal by high-pressure membranes. Fabrication variables that resulted in improved water flux and high levels of organic micropollutant rejection in TFCs and zeolite TFNs were identified, and it was found that these variables yielded similar trends in performance between the two membrane types. Further, it was demonstrated that IP in TFCs is not inherently self-limiting, and an innovative approach to TFC modification was developed using MPD permeation through TFC active layers to form additional polyamide. This approach was adapted to TFC fabrication, and identified as a novel variable to employ in the production of TFCs. High-pressure membranes were also found to be an effective treatment technology for PFAS removal and displayed a broad range of performance when treating PFAS-contaminated groundwater; PFAS rejection was highest among fully aromatic polyamide TFCs (including those modified with additional active layer formation) and lowest among semi-aromatic polyamide TFCs. Overall, this work provides valuable insights into TFC membrane modification and fabrication strategies that can be employed in the production of high-pressure membranes for enhanced organic micropollutant removal.Doctor of Philosoph
