Student assignments

Background

Membrane processes can significantly contribute to achieving the United Nations Sustainable Development Goals (e.g., 3, 6, 7, 12, 13) and are crucial for fundamental processes, e.g., water treatment and medical applications. However, membranes are mainly made from fossil-based raw materials using hazardous solvents. These membranes have unique properties (separation characteristics, mechanical stability), important for their respective applications making it challenging to replace them with more sustainable materials and fabrication procedures.

Polyelectrolytes are a promising replacement for conventional membrane materials. Water can be used as the solvent for polyelectrolyte membrane fabrication, replacing hazardous organic solvents like NMP and DMF.  Furthermore, bio-based polyelectrolytes can replace fossil-based raw materials. However, achieving the same separation characteristics and especially mechanical stability as fossil-based membranes is still a challenge.

Hence, this master’s thesis focuses on developing a new membrane fabrication method using an electron beam treatment for polyelectrolyte membranes to enhance the mechanical stability and potentially the membrane’s porous structure and, thus, the separation characteristics.

The work mainly focuses on:

• Screening of bio-based polyelectrolytes suitable for membrane fabrication.
• Fabricating bio-based polyelectrolyte membranes on lab-scale.
• Development of an electron beam post-treatment procedure for polyelectrolyte membranes.
• Characterizing membranes regarding their morphology, mechanical stability, and separation characteristics.

This assignment is suitable for both bachelor’s and master’s students.

If you’re interested and would like to know more about this project, contact Stefan Herrmann (s.herrmann@utwente.nl).

Background:

Water shortage is currently one of the world's most critical problems and is expected to increase in severity. It is predicted that by 2050, half of the world's population will live in areas with water shortages[1]. This highlights the need to explore alternative water sources. Brackish water, with salinity between freshwater and seawater, offers a promising supplementary source. Its lower energy demand for desalination makes it a viable solution for addressing future water shortages.

Polyelectrolyte multilayer (PEM) membranes are a promising and scalable technology for nanofiltration, offering excellent removal of organic micropollutants and high rejection of divalent ions [2]. However, their relatively high swelling ratio in aqueous and high saline environments, especially compared to interfacial polymerization membranes, can lead to low monovalent ion retention [3]. This project aims to develop dense and stable PEM-based nanofiltration (NF) membranes for brackish water treatment by testing novel hydrophobic polyelectrolyte pairs. Additionally, the membranes will be evaluated for their stability and performance in harsh conditions, ensuring they maintain their selectivity.

Keywords: Polyelectrolyte multilayers, nanofiltration, dense membranes

During this project, you will focus on:

• Conducting an in-depth review of current literature on PEM membranes, focusing on their working mechanisms, properties, and efficacy in water treatment applications. This review will cover key topics, including the properties of different polyelectrolytes, their ion selectivity behavior, and the latest innovations in PEM membrane technology.
• Fabricate PEM membranes using the layer-by-layer technique, focusing on dense membrane formation to enhance treatment efficiency.
• Performing experiments to evaluate the permeability, salt retention, and molecular weight cut-off (MWCO) of PEM membranes.
• Explore symmetric and asymmetric coating configurations for optimized membrane performance.
• Comparing the performance of dense PEM membranes with conventional NF membranes, focusing on improvements in monovalent ions selectivity.

 This project is ideal for master's students seeking hands-on experience in advanced water treatment technologies.

Reference:

[1]  F. R. Siegel, “Global Warming and Water 2050: More People, Yes; Less Ice, Yes; More Water, Yes; More Fresh Water, Probably; More Accessible Fresh Water?,” in The Earth’s Human Carrying Capacity: Limitations Assessed, Solutions Proposed, F. R. Siegel, Ed., Cham: Springer International Publishing, 2021, pp. 71–85. doi: 10.1007/978-3-030-73476-3_7.

[2]  E. Te Brinke, D. M. Reurink, I. Achterhuis, J. De Grooth, and W. M. De Vos, “Asymmetric polyelectrolyte multilayer membranes with ultrathin separation layers for highly efficient micropollutant removal,” Applied Materials Today, vol. 18, p. 100471, Mar. 2020, doi: 10.1016/j.apmt.2019.100471.

[3]  S. Dodoo, R. Steitz, A. Laschewsky, and R. von Klitzing, “Effect of ionic strength and type of ions on the structure of water swollen polyelectrolyte multilayers,” Phys. Chem. Chem. Phys., vol. 13, no. 21, pp. 10318–10325, May 2011, doi: 10.1039/C0CP01357A.

For more information, please contact: Sina Rezaei (Sina.rezaei@utwente.nl)

Previously, we have researched the influence of temperature gradients on the performance of electrodialysis experimentally [1,2] as well as numerically with a model system of ion selective nanochannels [3]. It was found that temperature differences can increase current at a given voltage (as expected from conductivity) and more interestingly that ion selectivity could be tuned based on these temperature differences due to variation in how the hydrated radius of ions change at different temperatures.

However, in an electrodialysis process, the salt concentration changes along the length of the membrane due to the electrical field, which drives the ions through the ion-exchange membrane. Therefore, more fundamental research into the effect of temperature and concentration gradients  on the transport rate of ions through a membrane is necessary to exploit these effects.

In this work, we plan to study ion and related transport phenomena through a bed packed with ion-exchange resin particles, while keeping the temperature gradient and concentration gradient nearly constant across the bed. Ion exchange resin particles are composed of  charged groups and therefore will preferentially allow the transport of counterions through the bed, while co-ions are retained by the ion exchange resin, which mimics a ion-exchange membrane. This setup allows to study the effect of concentration difference, electrical field strength, etc. on the rate of transport of different ions through porous ion exchange beds. This then has possible implications in how to improve industrially scale ion-exchange processes using low-grade waste heat.

This assignment can be suitable for either bachelor and master students.

If you’re interested and would like to know more about this project, then don’t hesitate to contact Jeff Wood (j.a.wood@utwente.nl).      

[1]: A. Benneker et al. Effect of temperature gradients in (reverse) electrodialysis in the Ohmic regime. Journal of Membrane Science 2018 p. 421-428.

[2]: A. Benneker et al. Influence of temperature gradients on mono- and divalent ion transport in electrodialysis at limiting currents. Desalination 2018 p. 62-69.

[3]: A. Benneker et al. Influence of temperature gradients on charge transport in asymmetric nanochannels. Physical Chemistry Chemical Physics 2017 vol. 19 (41).

Are you interested in contributing to the reduction of food waste? Do you like to understand how the chemistry and properties of membranes change when exposed to different environments? Then this project is for you.

Food systems are responsible for one third of the greenhouse gas (GHG) emissions (Crippa et al. 2021) and in the current food production systems 30-50% of food is wasted. To be able to feed the growing population (10 billion people by the decade of 2050 (United Nations 2022)) in a sustainable manner, recovering ingredients from food waste has become one of the priorities of governmental organizations and private companies, as most of this waste is perfectly edible and presents high nutritional value (e.g. proteins, sugars, etc.). The production of ingredients from food side streams is known as upcycling.

In this project, Greencovery and the Membrane Process Technology group of the University of Twente work together to understand how we can use membranes to reduce the energy consumption during the upcycling of food side streams. The project is part of a research consortium involving several companies (Recircanol https://ispt.eu/projects/recircanol/).

During the standard upcycling process ethanol is recovered using traditional methods like evaporation and distillation. Implementing membrane technology would help to reduce the environmental impact and production cost of the upcycling process. However, the ethanol containing stream also has a high pH, which presents a challenge for traditional organic solvent resistant/tolerant nanofiltration membranes (Othman et al. 2010). Therefore, further research is needed to implement membranes in the solvent recovery step.

BSc or MSc assignment

The assignment's objective is to evaluate the behavior and performance of different commercially available (nanofiltration)membranes on laboratory scale (focusing on flux, rejection), and to determine the impact of these changes on the process design.

During the project you will perform the experiments, evaluate the obtained data and interpretate the results. Also, you will develop your soft skills (time and stakeholders management, oral and written communication, independence and initiative).

The project will take place in the facilities of the Department of Membrane Science and Technology at the University of Twente.

This assignment is suitable for both bachelor and master students.

If you’re interested and would like to know more about this project, then don’t hesitate to contact Paco Caparros (f.caparrossalvador@utwente.nl).

• Crippa, M., E. Solazzo, D. Guizzardi, F. Monforti-Ferrario, F. N. Tubiello, and A. Leip. 2021. “Food Systems Are Responsible for a Third of Global Anthropogenic GHG Emissions.” Nature Food 2 (3): 198–209. https://doi.org/10.1038/s43016-021-00225-9.
• Othman, Rahimah, Abdul Wahab Mohammad, Manal Ismail, and Jumat Salimon. 2010. “Application of Polymeric Solvent Resistant Nanofiltration Membranes for Biodiesel Production.” Journal of Membrane Science 348 (1): 287–97. https://doi.org/10.1016/j.memsci.2009.11.012.
• United Nations. 2022. “World Population Prospects.” Summary of results. New York. https://www.un.org/development/desa/pd/sites/www.un.org.development.desa.pd/files/wpp2022_summary_of_results.pdf.

Are you interested in contributing to the reduction of food waste? Do you like to understand how the chemistry and properties of membranes change when exposed to different environments? Then this project is for you.

Food systems are responsible for one third of the greenhouse gas (GHG) emissions (Crippa et al. 2021) and in the current food production systems 30-50% of food is wasted. To be able to feed the growing population (10 billion people by the decade of 2050 (United Nations 2022)) in a sustainable manner, recovering ingredients from food waste has become one of the priorities of governmental organizations and private companies, as most of this waste is perfectly edible and presents high nutritional value (e.g. proteins, sugars, etc.). The production of ingredients from food side streams is known as upcycling.

In this project, Greencovery and the Membrane Process Technology group of the University of Twente work together to understand how we can use membrane technology to reduce the energy consumption during the upcycling of food side streams. The project is part of a research consortium involving several companies (Recircanol https://ispt.eu/projects/recircanol/).

During the standard upcycling process, ethanol is recovered using traditional methods like evaporation and distillation. Implementing membrane technology would help to reduce the environmental impact and production costs of the process. However, the ethanol containing stream also has a high pH, which presents a challenge for traditional organic solvent resistant/tolerant nanofiltration membranes (Othman et al. 2010). Therefore, further research is needed to implement membranes in the solvent recovery step.

BSc or MSc assignment

The objective of this assignment is to use computational fluid dynamics (CFD) to understand the impact of module configuration on the membrane performance  (flux, rejection) and overall nanofiltration process when working with ethanol-water-hydroxide mixtures.

You will simulate chemical species transport and fluid flow patterns for different membrane cell geometries, compare the simulation results with experimental data, and interpretate the results. Also, you will develop your soft skills (time and stakeholders management, oral and written communication, independence and initiative).

The project will take place in the facilities of the Department of Membrane Science and Technology at the University of Twente.

This assignment is suitable for either bachelor or master students.

If you’re interested and would like to know more about this project, then don’t hesitate to contact Paco Caparros (f.caparrossalvador@utwente.nl).

• Crippa, M., E. Solazzo, D. Guizzardi, F. Monforti-Ferrario, F. N. Tubiello, and A. Leip. 2021. “Food Systems Are Responsible for a Third of Global Anthropogenic GHG Emissions.” Nature Food 2 (3): 198–209. https://doi.org/10.1038/s43016-021-00225-9.
• Othman, Rahimah, Abdul Wahab Mohammad, Manal Ismail, and Jumat Salimon. 2010. “Application of Polymeric Solvent Resistant Nanofiltration Membranes for Biodiesel Production.” Journal of Membrane Science 348 (1): 287–97. https://doi.org/10.1016/j.memsci.2009.11.012.
• United Nations. 2022. “World Population Prospects.” Summary of results. New York. https://www.un.org/development/desa/pd/sites/www.un.org.development.desa.pd/files/wpp2022_summary_of_results.pdf.

Smart module design for precise solute separation using polyelectrolyte multilayer nanofiltration membranes (MSc assignment)

Nanofiltration (NF) has become a central pressure-driven membrane technology, bridging the gap between Ultrafiltration and Reverse Osmosis. NF membranes typically have a molecular weight cut-off (MWCO) in the range of 150–2000 Da, making them highly relevant for selective solute separation in water treatment. Among the different configurations, hollow fiber (HF) membranes are gaining importance because of their high packing density, compact footprint, and mechanically self-supporting structure that allows simple backwashing for fouling control.
In recent years, layer-by-layer (LbL) assembly of polyelectrolyte multilayers (PEMs) has emerged as a powerful route to fabricate HF NF membranes. This approach enables nanometer-scale control of selective layer thickness, surface charge, and chemistry, offering exceptional tunability for targeted separation applications.
While PEM membranes are often evaluated at the level of single fibers, such testing does not capture the dynamics encountered under real operating conditions. Shifting the focus to modules provides a more realistic assessment of performance, including scaling behavior, solute transport at higher recoveries, and overall system efficiency. This project therefore aims to design, fabricate, and test PEM membrane modules, providing insights into the opportunities and challenges of smart modular design.

Keywords: Membrane technology, polyelectrolyte multilayers, modular design.

During this project, you will:

• Review the existing literature on PEM membranes, focusing on their mechanisms, properties, and the behaviour of different polyelectrolyte pairs. Key topics will include the swelling behaviour, odd-even effects, symmetric vs asymmetric PEM membranes, and recent advancements in PEM membrane technology.
• Improve fabrication strategies such as partial dip coating to better control selective layer placement along hollow fibers, and design a protocol for assembling full-scale PEM membrane modules (1.5 m length).
• Characterize the modules by performing water permeability and molecular weight cut-off (MWCO) tests using Gel Permeation Chromatography (GPC). Gain proficiency in using the MExplorer cross-flow setup to test the fabricated modules in cross-flow mode.
• Investigate the impact of operational parameters such as pressure and recovery ratio on membrane performance, and evaluate solute retention through both single-salt and mixed-salt experiments to capture realistic separation behaviour.

Interested? Please contact Purvil Gangar (p.k.gangar@utwente.nl).
See also Design of novel charge-mosaic membrane processes (utwente.nl/mpt).

Removal of micropollutants from wastewater: pilot-scale investigation

Background

Organic micropollutants (OMPs), such as pharmaceuticals, personal care products, pesticides and stimulants, appear in trace amounts (µg/l- ng/l) in wastewater and surface waters. These compounds are a source of concern for their persistent nature and impose environmental risks when introduced into the ecological environment. Because they are not sufficiently removed in most existing wastewater treatment facilities, there is a need to develop more efficient and cost-effective technologies to remove them.

Pilot installation

This research is conducted using a pilot-scale installation, located at the wastewater treatment plant (WWTP) in Enschede. The wastewater influent for the pilot is collected after the WWTP primary clarifier. The wastewater contains a spectrum of different pollutants, ranging from common (biodegradable) organic compounds to suspended solids, nutrients and pollutants like OMPs, PFAS, etc. Ideally, these compounds need to be removed from the water cycle for >80%.  

The pilot is composed of  a biological reactor, where most of the common pollutants are removed (e.g. COD, nutrients, etc.) through biodegradation with sludge. The sludge is separated from the water matrix through a clarifier. Most of the suspended particles are collected at the bottom of the clarifier and then recirculated back to the biological reactor, to keep control of the bio-activity in those reactors. The effluent stream from the clarifier is connected to a nanofiltration (NF) membrane installation. The NF membranes retain substantial part of the OMP’s (amongst other compounds). The NF permeate stream is discharged into the surface water. The NF concentrate stream, which contains the OMP’s, is returned to the biological reactor.

Objective

The main objective of this MSc assignment is to optimize the operation of the nanofiltration pilot, such that the extent of OMP removal in the wastewater treatment pilot is maximized. Obviously, the operation of the biology reactor should not be affected, and a stable membrane operation should be guaranteed. The content of the MSc assignment will be determined in more detail together with the student, but most likely will involve process monitoring, laboratory analyses and experiments, along with process optimization.

Interested? Please contact Mostafa Elshourbagy (m.m.a.elshourbagy@utwente.nl). See also Micropollutant removal using nanofiltration and concentrate recirculation (utwente.nl/mpt).

Development and Characterization of Special RO Membranes for Brine Concentration

Highly saline (> 55 g/L) wastewater is produced by multiple industries [1]. The desalination industry alone produced more than 140 million m³ per day in 2019 [2]. Brine discharge is costly and has damaging effects on the environment [3]. Salts and water in the brine are valuable resources for recycling, and are wasted upon disposal. Therefore, it is desired to process brine to recover salt and water instead of discharging it. However, current thermal methods of brine separation are highly energy intensive [4]. Moreover, conventional membrane separation methods such as high pressure RO cannot be applied due to the excessively high pressures (>150 bars) required to overcome the osmotic pressure of the brine [5].

Osmotically assisted reverse osmosis (OARO) is an alternative technology that lowers the required pressures by providing salt solutions to both sides of the membrane [6] reducing the osmotic pressure difference over the membrane. This process will be used to split waste brine into concentrated and diluted streams. The dilute stream will then be processed into clean water, and the concentrated stream will be used as a source of salt. Thus, OARO will be explored as an alternative method for recovering water and salt from brine. The aim is to turn brine effluents into clean water and saturated salt solution (25 wt%), with an energy consumption lower than that of mechanical vapor recompression (<20 kWh/m³).

Master Thesis Assignment

Experimental studies have affirmed the applicability of OARO, but also showed that there is a significant loss in membrane flux under high salt concentrations [7,8]. A low flux negatively affects process economics. This MSc assignment focuses on evaluating commercial membranes under OARO conditions, and improving their characteristics through chemical treatments. The goal is to find those membranes and process conditions that minimize the energy consumption.

Emphasis is placed on the following aspects:

• Evaluating the water and salt fluxes of commercial membranes under OARO conditions, with varying salinity, pressure and crossflow velocity.
• Chemical treatment with alkylating agents, and characterization of the samples with zeta potential and FTIR spectroscopy measurements.
• Evaluating the water and salt fluxes of the treated membranes and comparison with the original membranes.
• Selection of the membrane and process conditions to model an OARO cascade.

Interested? Please contact Onur K. Aydın (o.k.aydin@utwente.nl).
See also Osmotically-assisted reverse osmosis (utwente.nl/mpt)

References

1. Panagopoulos A., Env. Sci. and Pol. Res., 29: 23736 (2022).
2. Jones E. et al., Sci. of the Tot. Env., 657: 1343, (2019).
3. Panagopoulos A. et al., Sci. of the Tot. Env., 693: 133545, (2019).
4. Vane L. M., Journal of Chem. Tech. & Biotech., 92: 2506 (2017).
5. Anvari A. et al., Desalination, 580: 117565, (2024).
6. Bargeman G., Sep. Purif. Technol., 293: 121113, ( 2022)
7. Togo, N. et al., Ind. & Eng. Chem. Res., 58: 6721,  (2019).
8. Turetta, M et al., Chem. Eng. Technol., 47: e202300553, (2024).

Characterization and development of low salt rejection RO membranes
for brine concentration

Due to increasing consumption of water and climate change, it is essential to recycle water so that less wastewater is discharged and more freshwater is recovered. Especially the industry produces a significant amount of brine with high salt concentrations, and the discharge of concentrated salt water shows a disturbance of the aquatic ecosystem. Therefore, it is essential to treat the brine properly [1]. Membrane-based technologies are very promising for brine treatment since they are more energy-efficient than thermal concentration processes. However, conventional reverse osmosis (RO) cannot replace thermal processes entirely due to the limited operating pressure for conventional reverse osmosis membranes. A technology to overcome this pressure limitation is the use of low salt rejection RO membranes, which are also known as loose RO membranes [2] [3]. These loose membranes have a salt retention between RO and NF membranes, which leads to a reduced osmotic pressure difference between concentrate and permeate [2]. As a result, the required transmembrane pressure is lower than that for RO membranes for a given concentration factor. Hence, LSRRO technology allows the production of concentrates with higher salt concentrations than achievable with conventional RO. To evaluate and improve LSRRO processes, membrane characterisation and development is essential.

Master Thesis Assignment

In this assignment, the focus is on characterising loose RO membranes under different salinities and pressures up to 120 bar. Commercially available RO membranes are treated with NaOCl or NaOH to make them looser. Additionally, the effect of various impurities and their corresponding levels on the membrane's performance will be investigated. To evaluate the performance of the membrane mainly the flux and the retention will be measured. Finally, these data are used in a process simulation to provide an initial indication of scale-up.

Emphasis is placed on the following aspects:

• Evaluating the retention and water and salt fluxes of loose RO membranes with varying salinity and pressure.
• Evaluating the effect of different impurities and impurity levels on the performance of the membrane.
• Process simulation by using experimental data for first indication of scale-up.

Interested? Please contact Lena S. Riechers (l.s.riechers@utwente.nl).
See also Low salt-rejection reverse osmosis (utwente.nl/mpt)

References

1. G. Bargeman, “Maximum allowable retention for low-salt-rejection reverse osmosis membranes and its effect on concentrating undersaturated NaCl solutions to saturation,” Sep Purif Technol, vol. 317, 2023, doi: 10.1016/j.seppur.2023.123854.
2. Z. Wang, A. Deshmukh, Y. Du, and M. Elimelech, “Minimal and zero liquid discharge with reverse osmosis using low-salt-rejection membranes,” Water Res, vol. 170, 2020, doi: 10.1016/j.watres.2019.115317.
3. Y. Du, Z. Wang, N. J. Cooper, J. Gilron, and M. Elimelech, “Module-scale analysis of low-salt-rejection reverse osmosis: Design guidelines and system performance,” Water Res, vol. 209, 2022, doi: 10.1016/j.watres.2021.117936.