No description available.

Dans le cadre de la thématique consacrée à la transition énergétique, le Laboratoire de Thermique Energétique et Procédés (LaTEP) travaille sur la géothermie profonde. Cette thèse se focalise sur l’étude de l’encrassement des échangeurs de chaleur de surface et plus spécifiquement sur la modélisation et la simulation de l’évolution d’un dépôt. L’encrassement conduit à des pertes d’efficacité et nécessite la mise en place de moyens de prévention ou de nettoyage, entraînant d’importants surcoûts. Le modèle général proposé décrit des réactions hétérogènes entre deux phases multi-constituantes, l’une liquide et l’autre solide. La phase liquide est une solution contenant des ions dilués dans un solvant, tandis que le solide est composé de constituants immobiles. L’électro-migration des espèces est prise en compte dans la description. L’interface entre les deux phases est le siège de multiples réactions hétérogènes. Les conditions aux limites faisant intervenir la vitesse de l’interface permettent le couplage complet entre les deux domaines. Ce modèle général est ensuite appliqué au cas particulier de l’encrassement d’un tube par formation de sels et résolu à l’aide de Comsol Multiphysics. La simulation d’un cas simplifié d’encrassement par le sulfate de baryum a permis d’analyser la phénoménologie de la croissance du dépôt et de mettre en évidence les effets des évolutions de la solubilité et de la cinétique via la chute de température dans le tube, ainsi que de la mobilité radiale des espèces par diffusion qui limite la croissance. L’électro-migration participe significativement au transport mais n’influence pas l’épaisseur du dépôt. L’hypothèse d’une réaction de cristallisation de la barytine instantanément équilibrée conduit à une forte surestimation de l’encrassement. La composition de l’eau est ensuite complexifiée afin d’étudier l’influence de la présence du chlorure de sodium à 1 mol.L-1, puis d’ions strontium et ainsi la co-précipitation de barytine et de célestine. / In the framework of the theme devoted to the energy transition, the “Laboratoire de Thermique Energétique et Procédés” (LaTEP) is working on deep geothermal energy. This thesis focuses on the study of the fouling phenomenon of surface heat exchangers and more specifically on the modelling and the simulation of the evolution of a deposit. Fouling leads to loss of efficiency and requires means of prevention and cleaning, leading to huge over-costs. The proposed general model describes heterogeneous reactions between two multi-component phases, one liquid and the other solid. The liquid phase is a solution containing ions diluted in a solvent, while the solid is composed of immobile constituents. Transport by electro-migration is taken into account in the description. At the interface between the two phases, multiple heterogeneous reactions occur. The boundary conditions involves the interface’s velocity and allow a complete coupling between the two domains. This general model is then applied to the particular case of fouling of a pipe by salt formation and is solved using Comsol Multiphysics. Simulation of a simplified case of fouling from barium sulfate allowed an analysis of the phenomenology of the deposit growth. It highlights the effects of changes in solubility and kinetics caused by the temperature drop in the tube, as well as the effect of radial mobility of the species by diffusion, limiting the growth. Electro-migration contributes significantly to transport but does not influence the thickness of the deposit. The hypothesis of an instantly balanced barite crystallization reaction leads to an overestimation of the fouling. In a second time, more species are added to the water’s composition in order to study the influence of the presence of sodium chloride at 1 mol.L-1. Finally, the addition of strontium ions leads to co-precipitation of barite and celestine.

Climate change, water stress, and rapid population growth have increased the need to manage water resources through innovative sustainable technologies. Decentralized systems such as membrane treatment trains have become increasingly important to provide high volumes of potable water to millions of people. Pressure-driven membrane systems have dominated separation processes due to their low cost, small footprint, ease of operation, and high permeate quality. Conventionally, pressure-driven membranes are classified into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). MF and UF membranes operate under low pressure (< 7 bar, <~100 psi). They can separate a variety of large particles such as bacteria, natural organic matter, suspended solids, and colloids. In contrast, NF and RO membranes are more energy-intense due to operating at high pressures (7 – 80 bar, ~100 – 1200 psi) and can remove small molecules such as ions, pharmaceuticals, and heavy metals. Fouling is a primary challenge with membranes that compromises the membrane performance, increases energy consumption, and reduces the membrane lifetime. Many strategies are used to address fouling, such as pre-treatment (pH adjustment, screening, coagulation), membrane modification (chemical and morphological properties), and membrane cleaning (physical, chemical). However, such strategies increase operational expenditures, produce waste products that can impact the environment, and negatively impact membrane lifetimes. Recently, electrically conductive membranes (ECMs) have been introduced to address the challenges with traditional membranes. They contain conductive surfaces that offer self-cleaning and antifouling properties across the surface in response to electrical potential externally applied to them. ECMs are advantageous as compared to traditional membranes because (a) they are more effective in treating foulants as they target foulants at the membrane/solvent interface, (b) they are more economical and environmentally friendly as they reduce the need for chemical consumption, and (c) they can be responsive to fouling conditions as their antifouling mechanisms can be easily manipulated by changing the applied current type (positive, negative, direct current, alternating current) to match the foulant. ECMs have been formed from all categories of membranes (MF, UF, NF, MD, FO, and RO) with a range of applications. Despite the remarkable progress in demonstrating their excellent antifouling performance, there are many hurdles to overcome before they can be commercialized. Two of these are (a) a fundamental understanding of their underlying mechanisms, (b) surface materials that can withstand extreme chemical and electrical conditions. In this work, we have comprehensively discussed antifouling mechanisms with respect to surface polarization and elaborated on the impact of electrically-induced mechanisms on four major fouling categories. i.e., biofouling, organic fouling, mineral scaling, and oil wetting. In addition, we characterized surface properties of a common electrically conductive composite membrane composed of carbon nanotubes (CNTs) and polyvinyl alcohol (PVA). We then investigated the impact of cross-linkers in CNT/PVA network on transmembrane flux, electrical conductivity, hydrophilicity, and surface roughness. In addition, we proposed standard, practical, and straightforward methodologies to detect and quantify the electrochemical, physical, and mechanical stability of ECMs, using chronoamperometry and cyclic voltammetry, an evaluation of polymer leaching from membranes, and micro mechanical scratch testing, respectively. Our methods can readily be extended to all membrane-based separation processes and different membrane materials (carbonaceous materials, ceramics, metal-based, and polymers). To demonstrate the antifouling properties of ECMs, we challenged ECMs with mixed-bacterial cultures in a flow-through system. Although ECMs showed high rejection, comparable flux, and excellent self-cleaning performance under application of electrical potential, understanding the relationship between applied electrical currents and antifouling mechanisms demands a well-controlled investigation. To this end, we quantified the impact of electrochemically-induced acidic conditions, alkaline conditions, and H2O2 concentration on model bacteria, Escherichia Coli. We first quantified the electrochemical potential of CNT-based ECMs in generating stressors such as protons, hydroxyl ions, and H2O2, under a range of applied electrical currents (± 0-150 mA). Next, these individual stressors with identical magnitude were imposed on E. Coli cells and biofilms in batch and flow-through systems, respectively. This thesis guides researchers to understand the underlying antifouling mechanisms associated with ECMs, how to match the mechanisms to the application of ECMs, and offers benchmarks for making practical ECMs. / Thesis / Doctor of Philosophy (PhD)

Today the medical field is struggling to decrease bacteria biofilm formation which leads to infection. Also, biomedical devices sterilization has not changed over a long period of time which has resulted in high costs for hospitals healthcare managements. The objective of this project is to investigate electro-dynamic effects by surface energy manipulation as potential methods for preventing bacteria biofilm growing on medical devices. Based on electrokinetic environments two different methods were tested: rejection bacteria dielectrophoretic forces feasibility by numerical simulations; and electrowetting-on -dielectric by the fabrication of golden interdigitated electrodes on silicon glass substrates covered by a Teflon layer. In the first experiment, numerical simulations of gold electrodes in buffer solution and frequencies were carried out to determine the forces required to reject bacteria. In the second experiment, interdigitated gold electrodes coated with a dielectric Teflon layer, were characterized in terms of breakdown voltage, dielectric adhesion and contact angle in terms of applied voltage. Finally the effect of EWOD on bacterial adhesion was tested. The project resulted in promising simulation results for bacteria rejection using dielectrophoresis due to the wide range of frequency that rejects the modelled bacteria. However, practical experiments such as electrowetting-on-dielectric must verify this at incubation times larger than 24 hours in spite of the Teflon non-adhesive properties. / <p>opponent Alex Grossm ann Colin</p> / VRI

<p>Medical devices are at risk of biofouling within seconds after implantation, which can lead to thrombus formation and bacterial contamination. These issues can negatively impact the performance and reliability of the device. Poly(vinyl chloride) (PVC) and polyurethane (PU) are popular synthetic polymers used in biomedical applications, but their hydrophobic nature makes them susceptible to biofouling. To improve their biocompatibility, their surfaces must be modified to be antifouling. However, achieving a thoroughly coated surface through homogeneous activation and effective modification with antifouling polymers remains a challenge, despite recent advancements in polymer surface modification. In this dissertation, we modified the surfaces of medical-grade PVC and PU using hydrophilic and biocompatible polymer brushes via wet chemistry approaches in an aqueous medium. Specifically, we activated the PVC surface with amino groups and then modified it with either modified or synthesized hydrophilic polymers end-capped with reactive groups. Additionally, we coupled a functionalized surface initiator to the activated PVC surface to allow the grafting of different hydrophilic polymers via conventional <em>in situ</em> free-radical polymerization. We followed a similar process to activate the PU surface with amino groups and then coupled a co-initiator derivative to allow the grafting of different hydrophilic polymers via conventional <em>in situ</em> free radical polymerization as a redox initiation system. All the modified surfaces of PVC and PU have exhibited a significant increase in wettability, as well as extremely effective antifouling effects against cell and bacterial adhesion. Overall, the findings of this work demonstrate the applicability of wet chemistry surface modification for PVC- or PU-based medical devices and supplies in biofouling-resistant applications. </p>

Aerobic (AeMBRs) and Anaerobic Membrane Bioreactors (AnMBRs) are an essential part of the advanced wastewater treatment options, which offer advantages in terms of higher effluent discharge and smaller footprints over the traditional wastewater treatment. This study evaluates the performance of (AnMBRs) by analyzing the cumulative effect of eleven physico-chemical parameters from the data obtained from the studies conducted from year 2000 onwards. Effect of various parameters such as Solid Retention Time (SRT), Hydraulic Retention Time (HRT), Mixed Liquor Suspended Solids (MLSS), influent Chemical Oxygen Demand (COD), Organic Loading Rate (OLR), influent COD, and temperature on the COD removal, methane production and membrane fouling were evaluated. Spearman’s correlation analysis was performed to investigate the impact of environmental and operational parameters on membrane fouling, COD reduction, EPS/SMP and methane production and explain the results. It should be noted that the literature used has all needed variables; incomplete data sets were removed for the regression analysis, in this case, the fouling rate may be estimated. Of these variables, the fouling rate was significantly correlated only with flux (r = 0.291, p =

No description available.

Marine biofouling has troubled mankind, both environmentally and economically, since they set sail, resulting in many undesired consequences such as increased drag, reduced maneuverability, increased fuel consumption and greenhouse gas emissions, and heightened maintenance costs. This problem is highly complex as it involves more than 4000 marine organisms with varying modes of adhesion and surface preferences as well as many aquatic environments. The common state-of-the-art approaches to contend with marine biofouling on the submerged surfaces of ships in seawater has antifouling (AF) and fouling-release (FR) surfaces. As AF coating systems utilize biocides which are often toxic to the environment to prevent settlement of biofoulants, the endeavors have been shifted towards non-toxic FR marine system. Many FR systems take advantage of low surface energy and modulus polydimethylsiloxane (PDMS) on their surface, while the recent attempts explored the simultaneous effect of PDMS and hydrophilic moieties (i.e. polyethylene glycol (PEG) or zwitterionic polymers) on an FR surface, known as amphiphilic surfaces. Thus, the work in this dissertation focused on attaining amphiphilic surfaces with desirable FR performance. The studies in this dissertation were investigated to deliver two goals: 1) Enhancing the (FR) fouling-release performance of previously developed coating systems; 2) Introducing novel fouling-release marine coatings with set criteria. To address the former, a series of amphiphilic additives containing PDMS and hydrophilic polymers (zwitterionic-based or PEG) were prepared in chapters two-five. These additives were incorporated in several previously developed FR coating systems in order to modify their surfaces and enhance their FR performance. To address the latter, two amphiphilic marine coating systems were explored for accessing durable, non-toxic, and effective FR surfaces using epoxy-amine crosslinking chemistry. Overall, the studies in this dissertation not only demonstrated viable FR surfaces with desirable performance against several representative marine organisms such as N. incerta, U. linza, C. lytica, barnacles, and mussels but also contributed a deeper understanding about the effect of amphiphilicity concentration/balance on surface and FR properties.

An engineered biological filtration (biofiltration) process treating a nutrient-enriched, low-alkalinity, organic-laden surface water downstream of conventional coagulation-clarification and upstream of an ultrafiltration (UF) membrane process was assessed for its treatment effectiveness. The impact of biofiltration pretreatment on UF membrane performance was evaluated holistically by investigating the native source water chemistry and extending the analysis into the drinking water distribution system. The biofiltration process was also compared in treatment performance to two alternative pretreatment technologies, including magnetic ion exchange (MIEX®) and granular activated carbon (GAC) adsorption. The MIEX®, GAC adsorption, and biologically active carbon (BAC) filtration pretreatments were integrated with conventional pretreatment then compared at the pilot-scale. Comparisons were based on collecting data regarding operational requirements, dissolved organic carbon (DOC) reduction, regulated disinfection byproduct (DBP) formation, and improvement on the downstream UF membrane operating performance. UF performance, as measured by the temperature corrected specific flux or mass transfer coefficient (MTC), was determined by calculating the percent MTC improvement relative to the existing conventional-UF process that served as the control. The pretreatment alternatives were further evaluated based on cost and non-cost considerations. Compared to the MIEX® and GAC pretreatment alternatives, which achieved effective DOC removal (40 and 40 percent, respectively) and MTC improvement (14 and 30 percent, respectively), the BAC pretreatment achieved the lowest overall DOC removal (5 percent) and MTC improvement (4.5 percent). While MIEX® relies on anion exchange and GAC relies on adsorption to target DOC removal, biofiltration uses microorganisms attached on the filter media to remove biodegradable DOC. Two mathematical models that establish an empirical relationship between the MTC improvement and the dimensionless alkalinity to substrate (ALK/DOC) ratio were developed. By combining the biofiltration results from the present research with findings of previous studies, an empirical relationship between the MTC improvement versus the ALK/DOC ratio was modeled using non-linear regression in Minitab®. For surface water sources, UF MTC improvement can be simulated as a quadratic or Gaussian distribution function of the gram C/gram C dimensionless ALK/DOC ratio. According to the newly developed empirical models, biofiltration performance is optimized when the alkalinity to substrate ratio is between 10 and 14. For the first time a model has thus been developed that allows for a predictive means to optimize the operation of biofiltration as a pretreatment prior to UF membrane processes treating surface water.

This dissertation addresses the role of individual fouling mechanisms on productivity decline and solute mass transport in nanofiltration (NF) of surface waters. Fouling mechanisms as well as solute mass transport mechanisms and capabilities must be understood if NF of surface waters is to be successful. Nanofiltration of surface waters was evaluated at pilot-scale in conjunction with advanced pretreatment processes selected for minimization of nanofilter fouling, which constituted several integrated membrane systems (IMSs). Membrane fouling mechanisms of concern were precipitation, adsorption, particle plugging, and attached biological growth. Fouling was addressed by addition of acid and antiscalent for control of precipitation, addition of monochloramine for control of biological growth, microfiltration (MF) or coagulation-sedimentation-filtration (CSF) for control of particle plugging, and in-line coagulation-microfiltration (C/MF) or CSF for control of organic adsorption. Surface water solutes of concern included organic solutes, pathogens, and taste and odor compounds. Solute mass transport was addressed by evaluation of total organic carbon (TOC), Bacillus subtilis endospores, gesomin (G), 2-methlyisoborneol (MIB), and threshold odor number (TON). This evaluation included modeling to determine the role of diffusion in solute mass transport including assessment of the homogeneous solution diffusion equation. A cellulose acetate (CA) NF was less susceptible to fouling than two polyamide (PA) NFs. NF fouling was minimized by the addition of monochloramine, lower flux, lower recovery, and with the use of a coagulant-based pretreatment (C/MF or CSF). NF surface characterization showed that the low fouling CA film was less rough and less negatively charged than the PA films. Thus the theory that a more negatively charged surface would incur less adsorptive fouling, due to charge repulsion, was not observed for these tests. The rougher surface of the PA films may have increased the number of sites for adsorption and offset the charge repulsion benefits of the negatively charged surface. The addition of monochloramine significantly reduced biodegradation and integrity loss of the CA membrane. PA membranes are inherently not biologically degradable due to their chemical structure. Monochloramination reduced the rate of fouling of the PA membrane but resulted in a gradual increase in water mass transfer coefficient and a decrease in TDS rejection over time, which indicated damage and loss of integrity of the PA membrane. Based on surface characterization by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectrometry (FTIR), the PA membrane degradation appeared to be chemically-based and initiated with chlorination of amide nitrogen and/or aromatic rings, which ultimately resulted in disruption of membrane chemical structures. The recommended Integrated Membrane System to control fouling of a surface water nanofiltration system is CSF monochloramine/acid/antiscalent„³monochloramine-tolerant NF. This IMS, at low flux and recovery, operated with no discernable fouling and is comparable to a groundwater nanofiltration plant with cleaning frequencies of once per six months or longer. A significant portion of the organic solutes including total organic carbon (TOC) passing through the membranes was diffusion controlled. Permeate concentration increased with increasing recovery and with decreasing flux for both PA and CA membranes. The influence was diminished for the PA membrane, due to its high rejection capabilities. Total rejection of spores used as pathogen surrogates was not achieved as spores were indigenous and high spore concentrations were used in all challenge studies; however, Integrated Membrane System spore rejection exceeded credited regulatory rejection of similar sized microorganisms by conventional treatment by several logs. Spore rejection varied by NF but only slightly by MF as size-exclusion controlled. There was no difference among spore rejection of IMS with and without in-line coagulation. Consequently, these results indicate membrane configuration (Hollow fiber>Spiral Wound) and membrane film (Composite Thin Film>CA) significantly affected spore rejection. Geosmin and methylisoborneol have molecular weights of 182 and 168 respectively, and are byproducts of algal blooms, which commonly increase taste and odor as measured by the threshold odor number (TON) in drinking water. Although these molecules are neutral and were thought to pass through NFs, challenge testing of IMS unit operations found that significant removal of TON, G and MIB was achieved by membrane processes, which was far superior to conventional processes. A CA NF consistently removed 35 to 50 percent of TON, MIB, and G, but did not achieve compliance with the TON standard of 3 units. A PA NF provided over 99 percent removal of MIB and G. Challenge tests using MIB and G indicated that size-exclusion controlled mass transfer of these compounds in NF membranes.