Overcoming major challenges for water reuse via membranes : boron removal and membrane fouling

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2022-05

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Membrane-based separations are promising candidates for achieving water security through treatment and reuse of nontraditional waters (e.g., industrial/municipal wastewater, produced water). However, nontraditional waters can be highly impaired and contain a plethora of contaminants, which poses challenges for conventional membrane processes to treat such waters. Two major challenges faced by conventional membranes that limit their expansion to new reuse opportunities are poor removal of small, neutral solutes and membrane fouling. This dissertation investigates the potential for conventional and novel membrane processes to remove boric acid – a small, neutral solute that prevents water reuse in agriculture since boron is toxic to some plants – and prevent membrane fouling during water treatment. Results of this dissertation show poor boron removal and membrane fouling by (in)organic constituents can be overcome via integration of conventional and novel membrane materials/processes in fit-for-purpose treatment trains. Potential solutions include electrodialysis pretreatment to remove ions that contribute to membrane fouling, thereby enabling pH adjustments to increase boron rejection, as well as ligand-functionalized membranes to remove boron through a capture-and-release mechanism. Incorporation of these and other novel technologies in fit-for-purpose treatment trains will expand reuse capabilities for highly contaminated waters. In addition to material/process advancements, this dissertation presents fundamental research on boron selectivity and membrane fouling that can be used to guide the design of future membrane processes. Boron transport in nonporous membranes is shown to depend on bulk properties of solutes (e.g., size, hydrophobicity) and membranes (e.g., cross-link density), as well specific solute-membrane interactions such as hydrogen bonding. Membrane fouling by organic foulants such as natural organic matter (NOM) occurs through calcium-induced aggregation of NOM in solution followed by aggregate deposition and formation of disordered membrane fouling layers. These results encourage the design of novel membranes to minimize foulant affinity without compromising small, neutral solute rejection; integration of such membranes in fit-for-purpose treatment trains (with proper pretreatment) will enable reuse of unexplored water sources to address water and energy challenges worldwide.

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