An investigation of 1,4-dioxane and enantiomeric ibuprofen mass transfer in a nanofiltration (NF) membrane process has been completed. Pilot-scale experiments using a 267 gallon per minute (gpm) split-feed, center-port NF process treating pH 6.5 groundwater revealed a consistent 12 percent removal of 1,4-dioxane despite the variable feed concentration (180 nanograms per liter (ng/L) to 38,400 ng/L) when the water flux and temperature were held constant. Bench-scale, flat-sheet NF membrane experiments treating pH 4.0 synthetic water displayed a 34.5 to 49.5 percent removal of racemic ibuprofen. Removal values were dependent on feedwater concentration (1 to 1,500 microgram per liter (µg/L)), pH, pressure, and water matrix. Although 1,4-dioxane was not found to exhibit adsorptive tendencies, as much as 25 percent of racemic ibuprofen adsorbed onto the metal surfaces of the testing equipment. Mass balances determined that ibuprofen's S-enantiomer was primarily responsible for the adsorption. Density functional theory (DFT) computations exposed a 6.4 cubic angstroms (Å3) smaller molecular volume and 1.10 x 10-29 coulomb-meters (Debye) longer dipole moment of S-ibuprofen than R-ibuprofen, which could explain the S-enantiomers stronger affinity to stainless-steel equipment components. The rejection of S-ibuprofen was consistently greater than R-ibuprofen, postulated by the dissimilar polarity of the two molecules outlined by DFT calculations. Feedwater ibuprofen concentration, pH, and operating pressure affected ibuprofen adsorption onto the equipment and membrane components. Contact angle measurements revealed a direct relationship between membrane hydrophobicity and adsorbed ibuprofen concentration. Langmuir and Freundlich isotherms accurately modeled S-ibuprofen adsorption. Therefore, at least 24 hours of equilibration is required prior to conducting hydrophobic solute membrane rejection studies. Additionally, application of the Homogeneous Solution Diffusion Model (HSDM) was found to provide accurate predictions of 1,4-dioxane and R-ibuprofen permeate content based on statistical analysis; however, the model was less predictive for the S-enantiomer due to adsorptive tendencies of the molecule.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd2020-1608 |
| Date | 01 January 2020 |
| Creators | Higgins, Carlyn |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations, 2020- |
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