Mechanical vibration for the control of membrane fouling in direct contact membrane distillation

One of the biggest challenges for direct contact membrane distillation (DCMD) in treating wastewater from flue gas desulfurization (FGD) is the rapid deterioration of membrane performance resulting from precipitate fouling. Chemical pretreatment, such as lime-soda ash softening, has been used to mitigate the issue, however, with significant operating costs. In this study, mechanical vibration of 42.5 Hz was applied to lab-scale DCMD systems to determine its effectiveness of fouling control for simulated FGD water. Liquid entry pressure and mass transfer limit of the fabricated hollow fiber membranes were determined and used as the operational constraints in the fouling experiments so that the observed membrane performance was influenced solely by precipitate fouling. Minimal improvement of water flux was observed when applying vibration after significant (~16%) water-flux decline. Initiating vibration at the onset of the experiments prior to the exposure of foulants, however, was promising for the reduction of membrane fouling. The water-flux decline rate was reduced by about 50% when compared to the rate observed without vibration. Increasing the module packing density from 16% to 50% resulted in a similar rate of water-flux decline, indicating that the fouling propensity was not increased with packing density in the presence of vibration

Direct contact ultrasound for fouling control and flux enhancement in air-gap membrane distillation

© 2019 Elsevier B.V. Air Gap Membrane distillation (AGMD) is a thermally driven separation process capable of treating challenging water types, but its low productivity is a major drawback. Membrane fouling is a common problem in many membrane treatment systems, which exacerbates AGMD's low overall productivity. In this study, we investigated the direct application of low-power ultrasound (8–23 W), as an in-line cleaning and performance boosting technique for AGMD. Two different highly saline feedwaters, namely natural groundwater (3970 μS/cm) and RO reject stream water (12760 μS/cm) were treated using Polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) membranes. Theoretical calculations and experimental investigations are presented, showing that the applied ultrasonic power range only produced acoustic streaming effects that enhanced cleaning and mass transfer. Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR FT-IR) analysis showed that ultrasound was capable of effectively removing silica and calcium scaling. Ultrasound application on a fouled membrane resulted in a 100% increase in the permeate flux. Cleaning effects accounted for around 30–50% of this increase and the remainder was attributed to mass transfer improvements. Contaminant rejection percentages were consistently high for all treatments (>99%), indicating that ultrasound did not deteriorate the membrane structure. Scanning Electron Microscopy (SEM) analysis of the membrane surface was used to confirm this observation. The images of the membrane surface demonstrated that ultrasound successfully cleaned the previously fouled membrane, with no signs of structural damage. The results of this study highlight the efficient and effective application of direct low power ultrasound for improving AGMD performance

Membranas nanoestructuradas, compuestas de capa fina y nanocompuestas para el tratamiento de aguas

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 06/11/2020. Tesis formato europeo (compendio de artículos)During last decades, population growth, climate change, natural disasters, uncontrolled urbanization, and pollution have left about one third of the world’s population without adequate access to drinking water. Water issue is expected to be more exacerbated in the coming decades, with water scarcity occurring globally and affecting even regions currently considered waterrich. Addressing this problem requires a great deal of adequate research to improve the efficiency of water use and wastewater treatment, as well as to mitigate the impacts of a wide variety of factors affecting water availability worldwide. Over the past twenty years, membrane filtration technology has become a significant separation methodology for drinking water production from saltwater (i.e. desalination) and wastewater (or groundwater), providing environmentally friendly and effective alternatives to conventional technologies. The main advantages of membrane filtration technology over conventional separation methods are its high removal capacity of particulates and microorganisms, very low thermal and chemical impact, flexibility of operation, modular design, moderate energy consumption and high cost effectiveness. The growth of the global membranes market is mainly the result of the impressive development of materials used for membrane fabrication and modification, improvements in membrane modules, and the progress of related systems, plants and equipment. However, the application of membranes in water treatment is limited by membrane fouling, which reduces water production rate, increases energy consumption, deteriorates membrane separation capability, and shortens membrane lifespan increasing, consequently, operation and maintenance costs. Particularly, organic and microbial fouling are the initial steps for biofilm formation, resulting in severe fouling problems in many environmental and engineered applications including membrane water filtration. Therefore, it is crucial the preparation of membranes with optimized surface properties, which induce a high fouling resistant capacity. This PhD thesis is focused on the preparation, characterization, modification and optimization of novel and advanced membranes with enhanced organic and microbial antifouling performance for the treatment, clearance and disinfection of different types of water as a sustainable way to increase drinking water availability and reduce water scarcity. First, an overview of the progress made during last few years on the preparation of novel membranes and their modification for water treatment by hydrostatic pressure and vapor pressure gradient membrane processes (i.e., microfiltration, MF; ultrafiltration, UF; nanofiltration, NF; reverse osmosis, RO; membrane distillation, MD and pervaporation, PV) is outlined in order to better understand the challenges and drawbacks that still need to be overcome for these membrane filtration technologies...Durante las últimas décadas, el crecimiento demográfico, el cambio climático, los desastres naturales, la urbanización descontrolada y la contaminación han dejado a aproximadamente un tercio de la población mundial sin acceso adecuado al agua potable. Se espera que el problema del agua se agrave aún más en las próximas décadas, habiendo escasez de agua en todo el mundo y afectando incluso a las regiones actualmente consideradas ricas en agua. Abordar este problema requiere una gran cantidad de investigación adecuada para mejorar la eficiencia del uso del agua y el tratamiento de aguas residuales, así como para mitigar los impactos de una amplia variedad de factores que afectan la disponibilidad del agua en todo el mundo. En los últimos veinte años, la tecnología de filtración por membrana se ha convertido en una metodología de separación significativa para la producción de agua potable a partir de agua salada (es decir desalinización) y aguas residuales (o aguas subterráneas), proporcionando alternativas ecológicas y efectivas respecto a las tecnologías convencionales. Las principales ventajas de la tecnología de filtración por membrana sobre los métodos de separación convencionales son su alta capacidad de eliminación de partículas y microorganismos, muy bajo impacto térmico y químico, flexibilidad de operación, diseño modular, consumo moderado de energía y alta rentabilidad. El crecimiento del mercado mundial de membranas es principalmente el resultado del impresionante progreso en los materiales utilizados para la fabricación y modificación de membranas, las mejoras en los módulos de membranas y la evolución de los sistemas, plantas y equipos relacionados. Sin embargo, la aplicación de membranas para el tratamiento de agua está limitada por el ensuciamiento de la membrana, lo que reduce la tasa de producción de agua, aumenta el consumo de energía, deteriora la capacidad de separación de la membrana y acorta la vida útil de la misma aumentando, en consecuencia, los gastos de operación y mantenimiento. Particularmente, el ensuciamiento orgánico y microbiano conforman las etapas iniciales para la formación de biopelículas, lo que da lugar a graves problemas de ensuciamiento en muchas aplicaciones ambientales y de ingeniería, incluida la filtración de agua por membrana. Por consiguiente, resulta crucial preparar membranas con propiedades superficiales optimizadas que induzcan una alta capacidad de resistencia al ensuciamiento. Esta tesis doctoral se centra en la preparación, caracterización, modificación y optimización de membranas novedosas y avanzadas con una eficiencia de anti-ensuciamiento “antifouling” orgánico y microbiano mejorada para el tratamiento, depuración y desinfección de diferentes tipos de agua como una forma sostenible de aumentar la disponibilidad de agua potable y reducir la escasez de agua. Primero, se ofrece una visión general del progreso realizado durante los últimos años en la preparación de nuevas membranas y su modificación para el tratamiento de agua mediante procesos de membrana con gradiente de presión hidrostática y presión de vapor (incluyendo microfiltración, MF; ultrafiltración, UF; nanofiltración, NF; ósmosis inversa, OI; destilación en membrana, DM y pervaporación, PV) con el objetivo de comprender mejor los desafíos y los inconvenientes que aún deben ser superados por estas tecnologías de filtración de membrana...Fac. de Ciencias FísicasTRUEunpu

Recent Advances in Organic Fouling Control and Mitigation Strategies in Membrane Separation Processes: A Review

Membrane separation processes have become increasingly popular in many industries because of their ability to treat wastewater and purify water. However, one of the main problems related to the processes is organic fouling, which can significantly reduce their efficiency and cause membrane damage. This review provides a summary of the various forms of organic fouling that can occur in membrane separation methods and examines the factors that lead to their development. The article evaluates the progress made in different techniques designed to manage and reduce organic fouling, such as physical cleaning methods, chemical cleaning agents, and modifications to the membrane surface, including ultrasonic and membrane vibration methods. The review also highlights recent advances in emerging 3D printing technology to mitigate membrane fouling. Finally, the review provides a brief summary of the conclusions and future directions for research in the field of organic fouling control and mitigation in membrane separation processes

Membrane distillation for the treatment of concentrated saline effluents – mechanism and mitigation of membrane fouling and wetting

Membrane distillation (MD) is an emerging low energy desalination technology, where low-grade heat source can be utilized to provide heat to the feed, offering an alternative solution to saline concentrate treatment. Yet, MD still suffers prominently from scaling, wetting and low flux. To overcome these problems, methods of fouling control are frequently investigated, such as process optimization by selecting the appropriate operational parameters and cleaning protocols, and refining the intrinsic properties of the membrane to meet the needs of membrane distillation, in terms of enhanced fouling/wetting resistance and reduced mass transfer resistance. This dissertation examined the fouling mechanisms in MD process by different substances in treating saline concentrates produced from coal seam gas generation, as well as the desalination of brackish groundwater. In particular, the fouling mechanisms of substances such as alkaline scalants, silica, and humic acids were studied. During the treatment of coal seam gas water with the presence of silica, magnesium formed porous structured depositions with silica, which caused a less severe flux decline as compared to the feed without silica. Initially, the precipitation of calcite was spotted, followed by the deposition of magnesium silicate and sodium chloride. The roles of fouling control via intermittent cleaning, mechanical agitations, as well as an integrated thermal crystallizer were investigated. As such, cleaning of the membrane prior to catastrophic membrane degradation is a critical operating protocol as an approach to the maintenance of membrane performance. It should be noted that the approaches to fouling control should be carefully selected according to the specific fouling mechanism by the pollutants present in the feed. While vigorous agitations might be undesirable in MD process for the treatment of inorganic feed, it was discovered that the application of an integrated thermal crystallizer could help sustain membrane performance and harvest crystals. On the other hand, high speed transverse vibration at 500 rpm was found to be effective in fouling control for the treatment of brackish groundwater concentrates with a considerable amount of humic aicds. This work also explored the effect of surface engineering on membrane performance for different MD processes. To be specific, two approaches to surface functionalization were investigated as the purpose of different MD applications, namely Janus hydrophobic-hydrophilic membrane and superhydrophobic surface. To fabricate a Janus membrane, a facile solution-immersion method in the dopamine solution was applied. Significant increase of flux measured in a submerged direct contact membrane distillation configuration was observed from the modified membrane by this approach. The thickness of the hydrophilic layer determined the flux values and the rejection rate for long-term operation in saline solution; the trade-off caused by these two parameters should be carefully examined during the design of membrane. The maximum flux enhancement achieved by the Janus membranes was 120 % as compared to the nascent membranes. To fabricate the superhydrophobic surface, the membrane was immersed in the dopamine solution, followed by the deposition of silica nano-particles and low surface energy material of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (PDTS). The modified membrane showed enhanced anti-fouling and anti-wetting properties in a submerged vacuum membrane distillation setup for the desalination of brackish groundwater concentrates and sodium chloride solution. Both modified membranes showed superior stability in long-term desalination processes for MD applications

Wastewater Treatment and Reuse Technologies

This edited volume is a collection of 12 publications from esteemed research groups around the globe. The articles belong to the following broad categories: biological treatment process parameters, sludge management and disinfection, removal of trace organic contaminants, removal of heavy metals, and synthesis and fouling control of membranes for wastewater treatment

Development of a novel corrugated polyvinylidene difluoride membrane via improved imprinting technique for membrane distillation

© 2019 by the authors. Membrane distillation (MD) is an attractive technology for desalination, mainly because its performance that is almost independent of feed solute concentration as opposed to the reverse osmosis process. However, its widespread application is still limited by the low water flux, low wetting resistance and high scaling vulnerability. This study focuses on addressing those limitations by developing a novel corrugated polyvinylidene difluoride (PVDF) membrane via an improved imprinting technique for MD. Corrugations on the membrane surface are designed to offer an effective surface area and at the same time act as a turbulence promoter to induce hydrodynamic by reducing temperature polarization. Results show that imprinting of spacer could help to induce surface corrugation. Pore defect could be minimized by employing a dual layer membrane. In short term run experiment, the corrugated membrane shows a flux of 23.1 Lm-2h-1 and a salt rejection of > 99%, higher than the referenced flat membrane (flux of 18.0 Lm-2h_asuf and similar rejection). The flux advantage can be ascribed by the larger effective surface area of the membrane coupled with larger pore size. The flux advantage could be maintained in the long-term operation of 50 h at a value of 8.6 Lm-2h-1. However, the flux performance slightly deteriorates over time mainly due to wetting and scaling. An attempt to overcome this limitation should be a focus of the future study, especially by exploring the role of cross-flow velocity in combination with the corrugated surface in inducing local mixing and enhancing system performance

Nano-gefunctionaliseerde membraandistillatiemembranen voor drinkwaterproductie uit zout of brak water

Abstract in English and GermanThe reported PhD research study was conceived from real water problems experienced by a rural community in South Africa (SA). Specifically, water quality in the Nandoni Dam situated in the Vhembe District, Limpopo Province, South Africa was assessed in order to determine its fitness for use, following complaints by community members using this water for drinking and domestic purposes. The dam supplies water to 55 villages with approximately 800 000 residents. At the inception of the study, there was little scientific information relating to the quality of the water in the dam. Water samples from various sites across the Nandoni Dam, a primary source of domestic water supply in the region, were collected through each season of the year over a period of 12 months to ascertain the concentrations of dissolved salts in the dam. Additionally, harmful polycyclic aromatic hydrocarbons (PAHs) and phenols were assessed. The concentrations of the ions contributing to water salinity were generally lower than the brackish water bracket (i.e. 500 – 30 000 mg/L) but too high for potable water. The concentration of the phenols was relatively higher than the threshold limit of drinking water. Therefore, the water sourced from the Nandoni Dam was found not suitable for human consumption and therefore required integrated water resource management, as well as robust and cost-effective water treatment especially since the salinity of the water was high even after treatment by a water treatment plant sourcing water from the dam. In an attempt to develop a suitable energy-efficient technology or system for complete removal of salts (desalination) from the salty water (including brackish water), electrospun polyvinylidene fluoride (PVDF) nanofibre membranes were synthesised and evaluated for removal of salts using the Direct Contact Membrane Distillation (DCMD) process. The nanofibre membranes were synthesised with combined high mechanical stability, porosity, and superhydrophobicity to prevent fouling and wetting while maintaining high salt rejection and water flux. Organically functionalised silica nanoparticles (f-SiO2NPs) were embedded on PVDF nanofibre membranes using an in-situ electrospinning technique for superhydrophobicity enhancement. These modified membranes displayed Young’s modulus of ~43 MPa and showed highly porous properties (~80% porosity, 1.24-1.41 μm pore sizes) with superhydrophobic surfaces (contact angle >150°). Membranes embedded with octadecyltrimethoxysilane (OTMS), and chlorodimethyl-octadecyl silane (Cl-DMOS), octadecyltrimethoxysilane (ODTS)-modified SiO2NPs were the most efficient; rejecting >99.9% of NaCl salt, with a water flux of approximately 30.7-34.2 LMH at 60°C, thus indicating their capacity to produce potable water. The superhydrophobic membranes were coated with a thin layer consisting of carboxylated multiwalled carbon nanotubes (f-MWCNTs) and silver nanoparticles (AgNPs) to reduce membrane fouling. The AgNPs and f-MWCNTs were uniformly distributed with size diameters of 28.24±1.15 nm and 6.7±2.1 nm respectively as evidenced by transmission electron microscopy (TEM) micrographs. The antibacterial AgNPs embedded in the PVDF nanofibre membranes inhibited the growth of Gram-positive Geobacillus stearothermophilus and Staphylococcus aureus as well as Gram-negative Pseudomonas aeruginosa and Klebsiella pneumoniae indicating their potential to prevent biofilm formation. Fouling tests were conducted using bovine serum albumin (BSA), sodium alginate, colloidal silica, and thermophilic bacteria effluent as model organic, inorganic, and bio-foulants, respectively, using DCMD. The uncoated membranes were characterised by a flux decays ranging from 30% to 90% and salt rejection decays ranging from 1.4% to 6.1%. Membrane coating reduced the flux and salt rejection decays to 10–24% and 0.07–0.75%, respectively. Although the initial flux decreased from 42 to 16 LMH when using coated membranes, the resistance of these coated membranes to water flux and salt rejection decays indicated that coating could be a suitable one-step solution for fouling mitigation in DCMD. The major challenge would be to design the MD membranes with architectures that allow a high-water flux to be maintained i.e., a highly porous layer. Furthermore, the volatile compounds bearing hydrophobic groups were pretreated to reduce their fouling capacity on PVDF nanofibre membranes. In this study, polyacrylonitrile (PAN) and polyethylene-imine (PEI) functionalised-PAN nanofibre membranes were synthesised and evaluated as a pretreatment for the removal of chlorophenol and nitrophenol from solutions. Under optimised experimental conditions, adsorption capacities ranging from 27.3 – 38.4 mg/g for PAN and PEI-modified nanofibres, respectively, were recorded. The PEI-functionalised nanofibres showed a high potential as a pretreatment step to be integrated to MD process. Ultimately an integrated water desalination system was developed. This involved a pretreatment filter (pore size ~100 μm) containing PEI-functionalised PAN nanofibre materials to reduce particulates and large molecules of dissolved organic/inorganic compounds from the water to be treated. In this research, it was observed that the pre-treatment step was not sufficient in removing all traces of compounds causing fouling of the superhydrophobic PDVF nanofibre membranes. As such, coating of the membranes with a thin hydrophilic layer and coupled with the filtration pretreatment step was found to provide fouling-resistance properties, high salt rejection, and low flux decays on brackish water collected at an estuary in Belgium and the Nandoni Dam in South Africa, demonstrating the potential of the MD separation process towards potable water recovery from brackish water.Het onderzoek in dit proefschrift was gebaseerd op concrete waterproblemen die een landelijke gemeenschap in Zuid-Afrika (SA) ervaart. In het bijzonder werd de waterkwaliteit in het Nandoni-reservoir in het Vhembe-district in de provincie Limpopo in Zuid-Afrika onderzocht, om te bepalen of dit water geschikt is voor gebruik, na klachten van leden van de gemeenschap die dit water gebruiken als drinkwater en voor huishoudelijk gebruik. Het reservoir levert water aan 55 dorpen met ongeveer 800.000 inwoners. Bij het begin van het onderzoek was er weinig wetenschappelijke informatie over de kwaliteit van het water in het reservoir. Watermonsters van verschillende locaties in het reservoir, dat een primaire bron van drinkwater is in de regio, werden gedurende verschillende seizoenen van het jaar verzameld over een periode van 12 maanden, om de concentraties van de meest voorkomende ionen in het reservoir te bepalen. Bovendien werden de concentraties van schadelijke polycyclische aromatische koolwaterstoffen (PAK's) en fenolen gemeten. De concentraties van de ionen die bijdroegen aan het zoutgehalte van het water waren in het algemeen lager dan de drempel om het water als brak water te bestempelen (dat wil zeggen 500 – 30 000 mg/l), maar waren te hoog voor drinkwater. De concentratie van de fenolen was hoger dan de limiet voor drinkwater. Daarom bleek het water afkomstig van het Nandoni reservoir niet geschikt voor menselijke consumptie. Een beter geïntegreerd waterbeheer is dus nodig om deze bron voor drinkwater te beschermen, naast een robuuste en kosteneffectieve waterbehandeling. Deze waterbehandeling moet vooral het zoutgehalte van het water naar beneden halen, maar ook de concentraties van fenolen. In een poging om een geschikte energie-efficiënte technologie of een systeem voor de volledige verwijdering van zouten (~ontzilting) uit brak water te ontwikkelen, werden elektrisch gesponnen polyvinylideenfluoride (PVDF) nanovezelmembranen gesynthetiseerd en beoordeeld op verwijdering van zouten met behulp van Direct Contact Membraandestillatie (DCMD). De nanovezelmembranen hadden een gecombineerde hoge mechanische stabiliteit, porositeit en superhydrofobiciteit, die hielp om vervuiling (fouling) en vloeistofintrede in de poriën (wetting) te voorkomen, terwijl een hoge zoutverwijdering en hoge waterflux doorheen de membranen gehandhaafd bleven. Organische gefunctionaliseerde silica-nanodeeltjes (f-SiO2NP's) werden nadien geïncorporeerd in de PVDF nanovezelmembranen met behulp van een in-situ elektrospinning techniek om zo een nog grotere superhydrofobiciteit te bekomen. Deze gemodificeerde membranen hadden een degelijke treksterkte (Young's modulus van ~ 43 MPa) en waren zeer poreus (~ 80% porositeit, 1.24-1.41 μm poriegrootte). Het oppervlak van de membranen vertoonde inderdaad superhydrofobe eigenschappen (contacthoek met water > 150 °). De membranen ingebed met octadecyltrimethoxysilaan (ODTS) SiO2NP's waren het meest efficiënt: ze toonden een zoutretentie van> 99.9% voor NaCl, bij een waterflux van ongeveer 30.7-34.2 l/(m².h) bij 60 ° C (ten opzichte van 20°C in het permeaat), wat aangeeft dat ze in staat zijn om drinkbaar water te produceren. De superhydrofobe membranen werden nadien ook gecoat met een dunne laag bestaande uit gecarboxyleerde multiwall-carbon nanotubes (f-MWCNT's) en zilver nanodeeltjes (AgNP's), in een poging om membraanvervuiling te verminderen. De AgNP's en f-MWCNT’s hadden uniforme diameters van respectievelijk 28,24 ± 1,15 nm en 6,7 ± 2,1 nm (zoals bleek uit transmissie-elektronenmicroscopie (TEM)). De antibacteriële AgNP's ingebed in de PVDF-nanovezelmembranen remden de groei van Gram-positieve Geobacillus stearothermophilus en Staphylococcus aureus bacteriën, evenals Gram-negatieve Pseudomonas aeruginosa en Klebsiella pneumoniae bacteriën. Dit toont het potentieel van deze membranen om biofilmvorming te voorkomen. Vervuilingsproeven (in DCMD) werden uitgevoerd met behulp van runderserumalbumine (BSA), natriumalginaat, colloïdaal silica, en thermofiele bacteriën - als respectievelijk organische, anorganische en biologische vervuiling. De niet-gemodificeerde membranen werden gekenmerkt door een fluxverval, met een daling van de flux met 30% tot 90%, naast een daling van de zoutretentie met 1.4% tot 6.1%. Bij de gecoate membranen daalde de flux slechts met 10-24% en de zoutverwijdering slechts met 0.07-0.75% respectievelijk. Hoewel de initiële flux ook afnam (van 42 naar ± 16 l/(m².h)) bij het gebruik van gecoate membranen, toonde de hogere weerstand tegen vervuiling van deze gecoate membranen aan dat deze coating een geschikte oplossing zou kunnen zijn tegen vervuiling in DCMD. Bovendien kan de synthese in één stap verlopen. De grootste uitdaging zal echter zijn om MD-membranen te ontwerpen waarbij de coating de oorspronkelijke waterflux/de porositeit van de membranen niet teveel verlaagt. Daarnaast werden gemodificeerde PVDF nanovezels geproduceerd om de verwijdering van vluchtige, hydrofobe stoffen (zoals fenolen) door adsorptie aan deze vezels te verhogen. Er werden polyacrylonitril (PAN) en polyethyleen-imine (PEI) gefunctionaliseerde PAN nanovezels gesynthetiseerd, waarna deze geëvalueerd werden als adsorbens (en dus voorbehandeling voor de membraanstap) voor chloorfenol en nitrofenol. Onder geoptimaliseerde experimentele omstandigheden werden adsorptiecapaciteiten tussen respectievelijk 27.3 en 38.4 mg / g voor PAN- en PEI-gemodificeerde nanovezels gemeten. De PEI-gefunctionaliseerde nanovezels vertoonden een hoog potentieel als een voorbehandelingsstap voor de hierboven beschreven DCMD. Tenslotte werd ook een geïntegreerd waterontziltingssysteem ontwikkeld. Dit systeem bestond uit een voorbehandelingsstap met PEI-gefunctionaliseerde PAN-nanovezels (in de vorm van een membraan met poriegrootte ~100 μm), gevolgd door een gemodificeerde DCMD stap. De voorbehandeling diende om deeltjes en grote opgeloste organische verbindingen uit het te behandelen water te verwijderen voor de DCMD-stap. In dit onderzoek werd waargenomen dat de voorbehandelingsstap niet voldoende was om alle organische contaminanten te verwijderen die vervuiling veroorzaakten op de superhydrofobe PDVF nanovezelmembranen in de DCMD-stap. Toch bleek coating van de DCMD membranen met een dunne hydrofiele laag (gekoppeld aan de voorbehandelingsstap) een voldoende bescherming tegen vervuiling te bieden zodat de zoutretentie en waterflux van deze membranen hoog bleef. De combinatie van voorbehandeling – gemodificeerde DCMD werd succesvol getest op water uit de Schelde en uit het Nandoni reservoir, waarmee het potentieel van de technologie om drinkwater uit brak water te produceren werd aangetoond.School of SciencePh.D. (Applied Biological Science : Environmental Technology

Challenges in biogas production from anaerobic membrane bioreactors

© 2016 Spectacular applications of anaerobic membrane bioreactors (AnMBRs) are emerging due to the membrane enhanced biogas production in the form of renewable bioresources. They produce similar energy derived from the world's depleting natural fossil energy sources while minimizing greenhouse gas (GHG) emissions. During the last decade, many types of AnMBRs have been developed and applied so as to make biogas technology practical and economically viable. Referring to both conventional and advanced configurations, this review presents a comprehensive summary of AnMBRs for biogas production in recent years. The potential of biogas production from AnMBRs cannot be fully exploited, since certain constraints still remain and these cause low methane yield. This paper addresses a detailed assessment on the potential challenges that AnMBRs are encountering, with a major focus on many inhibitory substances and operational dilemmas. The aim is to provide a solid platform for advances in novel AnMBRs applications for optimized biogas production

Immobilized graphene oxide-based membranes for improved pore wetting resistance in membrane distillation

Membrane distillation (MD) is a useful method for the purification of difficult feedwaters but it cannot be applied in a range of industries due to pore wetting. In this work, graphene oxide (GO) laminate coatings are explored to overcome the pore wetting issues. Air gap MD (AGMD) configuration was considered, using a 35 g L-1 NaCl solution with 150 mg L-1 (150 ppm) of Triton X-100 surfactant as feed material. The GO is deposited as a laminate membrane on top of a commercial porous polyvinylidene fluoride (PVDF) support and good adhesion is achieved through the use of polydopamine (PDA) to form a hydrophilic tri-layer membrane. The small pore size achieved with the laminate GO led to increased pore wetting resistance for at least 90 h compared to 20 min with pristine commercial PVDF. Additionally, the extra layers of GO and PDA did not affect the membrane flux. Overall, a tri-layer immobilized GO membrane is synthesized with superior performance when compared to current commercial membranes, meaning that MD can be used for a new range of wastewater applications