He taught me what it means to develop a fundamental understanding of the real world, as well as how to convey that in a way that moves the field forward. To the current students, Ruoyu Wang, Rui Chen, Joshua Livingston, Weifan Liu, Siyuan Feng, Xudong Zhang, Sizhuo Zhang, Sk Md Ali Zaker Shawon, Abigail Cafferty and Juhyeon Roh: I wish you the best of luck and am excited to see each other in the future cross. You all gave me an outlet outside of the lab to have fun and blow off steam.
To my loving girlfriend, Kaylee, thank you for your love and support during this time. Last but not least, thanks to my little sister, Bailey, and my dad, Tom, for always being there for me and encouraging me to be the best I can be.
INTRODUCTION
- Brine Management and the Urgent Need for a More Practical Solution
- Membrane Distillation
- Electrodialysis
- Objectives and Hypotheses
- Structure of Dissertation
The overall objective of this thesis is to elucidate failure mechanisms and evaluate the performance of new brine handling and ZLD technologies. In connection with ED, the main objective is to develop and evaluate the practical applicability of ED in a new application for ZLD and mineral crystal recovery. The first objective is to demonstrate the influence of surface wetting properties and the interfacial gas layer charge on the scaling kinetics.
The second objective is to systematically study the effect of surface wetting properties, i.e., surface texture and surface energy, on organic fouling. The fourth objective is to demonstrate the new recovery process of ZLD and mineral crystals called electrodialytic crystallizer (EDC).
MEMBRANE WETTING PROPERTIES AND THEIR ROLE IN INORGANIC
- Introduction
- Materials and Methods
- Chemicals
- Surface Fabrication and Characterization
- Solvent Exchange and Scaling Experiments
- Quartz Crystal Microbalance Experiments
- Mineral Scaling Characterization
- Results and Discussion
- QCM-D response to gas layer formation and mineral scaling
- Surface Wetting Properties
- Gas layer formation: impacts of surface wetting property and bubble generation method
- Impacts of gas layer formation on mineral scaling kinetics
- Conclusions and Implications
The magnitude of the positive frequency shift increased from 13 ± 7 Hz on the hydrophilic surface in the surface bubble experiment to 28 ± 5 Hz in the bulk bubble experiment, likely due to the increased coverage of surface bubbles as bubbles were adsorbed from the bulk solution [101] . Top row) Frequency shifts recorded during the control, surface bubble, and bulk bubble experiments in this study on the (A) hydrophilic surface, (B) hydrophobic surface, and (C) superhydrophobic surface. Similarly, the final mass of crystals deposited on the surface decreased with the opacity of the surface bubbles.
The SEM-EDX map confirms that approximately half the amount of mineral crystal was deposited on the hydrophilic surface during the solvent exchange of the surface bubbles compared to the control solvent exchange with the degassed solution (Figure 2.10). For example, approximately half the mineral crystal deposition was observed on the hydrophobic surface compared to the hydrophilic surface in the absence of a submerged gas layer in the control solvent exchange experiment (Figure 2.9D & 2.10).
MEMBRANE WETTING PROPERTIES AND THEIR ROLE IN ORGANIC
- Introduction
- Materials and Methods
- Fabrication of surfaces with roughness
- Functionalization of surfaces to impart different surface energies
- Characterizations of morphology and wetting property
- Colloidal probe force spectroscopy
- Results and Discussion
- Morphologies of the surfaces
- Wetting properties of the smooth and rough surfaces
- Colloidal Probe Force Spectroscopy
- Adhesions between the colloids and the surfaces
- CONCLUSIONS
The surface morphology of the smooth and textured model surfaces was observed using both scanning electron microscopy (5 kV, secondary electron detector HE-SE2, SEM, Merlin, Zeiss, Thornwood, NY) and AFM-based force spectroscopy (ScanAsyst mode, Dimension Icon, Bruker, Billerica, MA). The static liquid contact angles (CA) of the surfaces were measured with water in air and with mineral oil under water. The surface morphology of the smooth and textured surfaces was also measured via AFM (Figure 3.2C and 3.2D, respectively).
The corresponding AFM images of the surfaces of (C) the smooth, pristine glass slide and (D) the rough SiNPs surface-coated slide. In comparison, in-air water CA of the PEG-grafted rough surface was not detectable, suggesting that the surface was rendered superhydrophilic. In-air water contact angles of the smooth PEG-grafted surface, the rough PEG-grafted surface, the smooth FAS-deposited surface, and the rough FAS-deposited surface.
Underwater oil contact angles on the smooth PEG-grafted surface, the rough PEG-grafted surface, the smooth FAS-deposited surface, and the rough FAS-deposited surface. The introduction of roughness to the surface improved the apparent CA of the hydrophobic surface. The surface roughness increased the underwater oleophilicity of the FAS-grafted surface, which reduced the underwater oil CA from to.
Adhesion force statistics of the polyethylene (PE) and carboxylate-coated polystyrene (C-PS) colloidal probes interacting with the smooth and rough hydrophilic PEG-grafted surfaces and smooth and rough hydrophobic FAS-grafted surfaces. The hydrophilic surfaces favor contact with water (i.e. surface hydration, 𝛾𝑃𝐿 < 𝛾𝑃𝑆 and 𝛾𝑆𝐿 < 𝛾𝑃𝑆), so the colloidal probe pulls away from the surface and replaces the area with the substrate𝑴 s the net interfacial energy of the three-phase system [193] . Likewise, with the same morphology of the hydrophilic surfaces, the maximum adhesion forces measured with the C-PS colloidal probe are smaller than those measured with the PE colloidal probe.
ENHANCE FOULING RESISTANCE OF MEMBRANE DISTILLATION
- Introduction
- Materials and Methods
- Materials and Chemicals
- Fabrication of a Superhydrophobic Membrane
- Membrane Characterization
- Membrane Scale Purging Experiments
- Results and Discussion
- Membrane Surface Properties
- Membrane Scaling and Effect of Purging
- Mechanisms of Scale Mitigation via Purging
- Implications
These studies showed that purification was only effective when the initial feed concentration was well above saturation, so that most of the crystals formed in the bulk solution and deposited on the membrane surface. The APTES-functionalized surface of the PVDF membrane was placed in contact with the SiNP dispersion for adsorption of SiNPs to the surface via electrostatic interaction. Since only the surface of the membrane was functionalized, the bulk of the membrane retained its hydrophobicity and thus floated on the SiNP dispersion, adding SiNPs only to the surface.
The change in surface morphology is confirmed by comparing the SEM images of the PVDF membrane (Figure 4.4A) and the superhydrophobic membrane (Figure 4.4B). The SA of the commercial hydrophobic PVDF membrane is not reported as it was not measurable; i.e., the droplet remained attached even with an inverted membrane surface. The appearance of membrane surfaces after MD experiments [with cleaning (Figure 4.5C)] differs dramatically between hydrophobic and superhydrophobic membranes.
Furthermore, the CA of the clear parts of the cleaned superhydrophobic membrane decreased very slightly to 160 ± 6°. Such CA was measured directly on the dried part of the membrane after it had been removed from the MD experiment without further purification. With superhydrophobic membranes, the crystals on the nonpurified membrane and the small fraction along one edge of the purified membrane (Figure 4.7C inset).
The excellent Cassie−Baxter condition achieved with the superhydrophobic membrane minimizes the penetration of the feed solution into the membrane pores and prevents the formation of crystal “anchors” within the membrane pores (Figure 4.7D). The photographic images in the center are the same as those in Figure 4.5C. A) Top-down SEM image of the scale layer on the surface of the hydrophobic membrane. Top-down SEM images of the crystal-free region of the superhydrophobic membrane surface (main figure) and the small rod-shaped crystals along the edge of the superhydrophobic membrane surface (field).
A NOVEL, NON-EVAPORATIVE APPROACH TOWARD BRINE
- Introduction
- Materials and Methods
- Materials and Chemicals
- Electrodialytic Crystallizer Experiments
- System Evaluation and Optimization Experiments
- Membrane Comparison Experiments
- Crystallization Criterion Experiments
- Results and Discussion
- System Evaluation and Optimization
- Membrane Comparison
- Crystallization Criterion
- Conclusions and Implications
Third, low salinities in conventional ED result in greater voltage drop across the ion exchange membranes in the ED stack. Crystal formation led to blockage of process flows and the ED cell, risking process failure in the proof-of-concept system. After selecting the most suitable ion exchange membrane, we evaluated which salts could be successfully crystallized in the improved EDC system.
The proof-of-concept system had no MF cell (option 1 in red), while the improved system had an integrated MF cell (option 2 in green). B) Total suspended solids (TSS) production rate in a proof-of-concept EDC system. However, there is a trade-off between the initial amount of salt required to saturate the brine and the energy required to cause temperature fluctuations in the crystallizer. However, in the proof-of-concept EDC system (Figure 5.3A, option 1 in red without MF), the suspended crystals left the crystallizer and flowed through the EDC system.
Like the proof-of-concept system, increased salt transport due to increased current density resulted in increased crystallization kinetics in the improved system. However, TSS at any given time increased by an approximate factor of 4 in the improved system compared to the proof-of-concept system (Figure 5.3D). Brine (circles) and dilute (triangles) conductivity in (A) the proof-of-concept system and (B) in the improved system (two systems depicted in Figure 5.1).
Theoretically, the effect of water transport due to osmosis and electro-osmosis can limit the maximum achievable concentration in the brine flow [270]. Otherwise, the salt in the brine stream will be diluted below the solubility limit and crystals will not form. Salt hydration number (blue) and molar ratio of salt to water at the solubility limit at 20°C (orange) for the salts successfully crystallized in the EDC system.
CONCLUSIONS AND FUTURE WORK
Hong, Recovery of water and minerals from shale gas produced water by membrane distillation crystallization, Water Res. Lin, Membrane fouling and wetting in membrane distillation and their mitigation by novel membranes with special wettability, Water Res. Lin, Wetting, Scaling, and Fouling in Membrane Distillation: Advanced Insights into Fundamental Mechanisms and Mitigation Strategies, ACS ES&T Eng.
Li, Smooth for scale resistance in membrane distillation: a novel porous micropillared superhydrophobic surface, Water Res. A Nanobubble-Assisted Scale Inhibition in Membrane Distillation for the Treatment of High Salinity Brines, Water Res. Elimelech, Relating organic fouling in membrane distillation to intermolecular adhesion forces and interfacial energies, Environ.
Wang, Novel membrane surface modification to improve anti-oil fouling properties for membrane distillation applications, J. Lin, Composite membrane with electrospun multi-scale textured surface for robust resistance to oil fouling in membrane distillation, J. Lin, Highly effective scaling mitigation in membrane distillation using a superhydrophobic membrane with gas purification, Environ.
Elimelech, Developed Smooth Surface to Mitigate Gypsum Deposits in Membrane Distillation for Treatment of Hypersaline Industrial Wastewater, Environ. Cheng, Preparation of Omniphobic PVDF Membranes with Silica Nanoparticles for Coke Wastewater Treatment Using Direct Contact Membrane Distillation: Electrostatic Adsorption Vs. Fane, Optimization of operating conditions for a continuous membrane distillation crystallization process with zero discharge of brine, J.
Chung, Development of simultaneous membrane distillation-crystallization (SMDC) technology for the treatment of saturated brine, Chem. Chen, Scale limitation in submerged vacuum membrane distillation and crystallization (VMDC) with periodic air backwashing, J.
