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Development of functionalized nanostructured polymeric membranes and related manufacturing processes for water purification

Final Report Summary - NANOPUR (Development of functionalized nanostructured polymeric membranes and related manufacturing processes for water purification)

Executive Summary:
The NANOPUR-project aimed at the development of intensified water treatment concepts based on nano-structured and nano-functionalized membranes for micropollutants and virus removal.
Today, membrane processes are already used for removing micropollutants and viruses from water streams. However, high pressure is required to push the water through the membrane and frequent cleaning procedures are needed. For example, the energy consumption of reverse osmosis processes is about 500 times higher than the energy needed to operate the membranes that are being developed in the framework of this project. Therefore, the newly developed membranes should show improved retention of viruses and micropollutants while high fluxes can be maintained by reducing the fouling propensity. The key concept was to overcome the frustration at the seemingly unbreakable linkage that exists between lower flow rates and high retention for the production of safe and pure drinking water. The ultimate “challenge” of the project existed in the creation of artificial membranes able to perform separations with the selectivity of biological membranes while having a mechanical strength and productivity of state-of-the-art artificial membranes.
In a first technology path, which targeted the preparation of ultrafiltration (UF) membranes with higher permeability while maintaining their pore size, non-solvent induced phase separation (NIPS) processes were used to prepare membranes from PVDF and polysulfone polymers. Optimized process conditions in combination with the use of newly developed copolymer additives have resulted in UF membranes with improved structure and antifouling properties, giving rise to higher fluxes without increasing the pore size of the membrane, and representing a significant progress beyond the state-of-the-art. In the final phase of the project, production of the newly developed membranes was scaled-up to pilot level.
In parallel to the work on membrane preparation, atmospheric plasma technology was evaluated for hydrophilization and functionalization of membranes. This approach was successful with evident hydrophilization across the section of the inert membranes. A decrease of the water contact angle of microfiltration membranes from more than 100 ° to less than 20 ° could be obtained. A very challenging and important aspect of this process was the water resistance of the plasma treatment which was also successfully demonstrated during long-term pilot-tests.
The newly developed and more efficient UF membranes and the plasma functionalization of membranes both comply with the cost and scalability requirements for industrial application as determined by the industrial partners and end-users at the start of the project and industrial implementation is considered to be feasible in a short term.
The second technology path focused on the selection and synthesis of affinity ligands for capture of the selected viruses and micropollutants. Antibodies are the most common recognition element utilized in affinity capture and they can be raised against most micropollutants with very high binding affinity and specificity. Antibodies are however very expensive and show a lack of stability in the conditions in which the membranes developed within NANOPUR are to be used. As an alternative to antibodies, Molecular Imprinted Polymer (MIP) nanoparticles with very high binding affinity for selected micropollutants and viruses, good stability and possibilities for up-scaling and regeneration were synthesized. The MIPs nanoparticles could be immobilized onto microfiltration membranes and were used for the selective uptake of micropollutants from contaminated water at high water fluxes.
The combined use of the nano-structured low-fouling ultrafiltration membrane and the microfiltration membrane functionalized with affinity ligands should allow the production of safe drinking and process water, both in Point of Use (POU) or Point of Entry (POE) applications, with much lower energy consumption than state-of-the-art membrane processes.
In parallel with the experimental developments, nano-scale modelling of the membrane surface and systematic up-scaling to the module-level was carried out to allow simulation of membrane performance as a function of micro- and nano-scale material parameters. In addition, a decision support system was developed to identify the best possible compromises between cost and performance.
The Environmental, Health and Safety (EHS) aspects and the Life Cycle (LCA) of the newly developed materials and technological routes have been carefully assessed.

Project Context and Objectives:
The NANOPUR-project aimed at the development of intensified water treatment concepts based on nano-structured and nano-functionalized membranes for micropollutants and virus removal.
Today, membrane processes are already used for removing micropollutants and viruses from water streams. However, high pressure is required to push the water through the membrane and frequent cleaning procedures are needed. For example, the energy consumption of reverse osmosis processes is about 500 times higher than the energy needed to operate the membranes that are being developed in the framework of this project. Therefore, the newly developed membranes should show improved retention of viruses and micropollutants while high fluxes can be maintained by reducing the fouling propensity. The key concept was to overcome the frustration at the seemingly unbreakable linkage that exists between lower flow rates and high retention for the production of safe and pure drinking water.
The ultimate “challenge” of the project existed in the creation of artificial membranes able to perform separations with the selectivity of biological membranes while having a mechanical strength and productivity of state-of-the-art artificial membranes. In quantitative terms, the objective of this project was to develop nano-structured membranes characterized by a selectivity towards pathogens of up to 99.99999 % and towards micropollutants up to 99 %, while retaining a permeability higher than current ultrafiltration membranes in addition to functional stability equal to existing commercial membranes.
Research activities involved the development of technologies to prepare polymeric nanostructured membranes characterised by well-controlled architectures and functions for supramolecular recognition for removal of viruses, endocrine disrupting compounds (EDRs), endotoxins and antibiotics from water. The technological developments were carried out along two different technology paths each targeting at a different aspect of the water treatment process. The first technology path focused on the preparation of ultrafiltration membranes with superior pore structure and stability in order to reduce membrane fouling, thereby enhancing the flux. The main objective of the second technology path existed in the development of affinity ligands for functionalization of membranes to allow removal of micropollutants and disinfection, without the need for decreasing the pore sizes of the membrane and adversely affecting the water flux. The combined use of both membranes should allow the production of safe drinking or process water at reduced energy consumption in comparison with state-of-the –art membrane processes.
For both technology paths, up-scaling to and evaluation at the pilot level was foreseen to evaluate the prospects of the newly developed technologies and to allow the evaluation of the cost, the economic viability and the scalability of the proposed solutions.
In parallel with the experimental developments, nano-scale modelling of the membrane surface and systematic up-scaling to the module-level should allow simulation of membrane performance as a function of micro- and nano-scale material parameters. The development of a decision support system should facilitate the identification of the best possible compromises between cost and performance.
Finally, assessment of the Environmental, Health and Safety (EHS) aspects and the Life Cycle (LCA) of the newly developed materials and technological routes should be carried out in detail.

Project Results:
The technological developments in this project were carried out along two different technology paths each targeting at a different aspect of the water treatment process.
The first technology path focused on the preparation of ultrafiltration membranes with superior pore structure and stability in order to reduce membrane fouling, thereby enhancing the flux. The main objective of the second technology path existed in the development of affinity ligands for functionalization of membranes to allow removal of micropollutants and disinfection, without the need for decreasing the pore sizes of the membrane and adversely affecting the water flux. The combined use of both membranes should allow the production of safe drinking or process water at reduced energy consumption in comparison with state-of-the –art membrane processes.
With respect to the development of new synthesis routes for UF membranes, the most relevant scientific and technological progress beyond the state-of-the-art is related to the findings that structure and UF performance including antifouling properties of PVDF membranes can be significantly improved by the synergistic combination of the established and newly developed block-copolymer additives. In addition, also optimization of Vapour phase and Non-solvent induced Phase Separation (VIPS/NIPS) processes has resulted in improved water permeability and molecular weight cut-off of PVDF membranes. The hydrophilization and functionalization of MF and UF membranes by means of atmospheric plasma technology is in particular novel due the water stability of the treatment that could be obtained by applying a 2-step approach. This project result is protected by 2 patent applications in which also a novel electrode concept for treatment of porous materials is included. With respect to industrial up-take of the results is of particular importance that the VIPS and the NIPS technology as well as plasma-treatment of membranes could be scaled-up successfully to pilot scale level.
In the second technology path, which dealt with the development of affinity membranes, molecular imprinted polymer (MIP) nanoparticles with affinity for micropollutants and viruses were synthesised. Very high binding affinities of the synthesized MIPs for the target molecules/viruses were obtained, representing a significant progress beyond the state-of-the-art. The binding affinities obtained for the MIPs were in the same range as the binding affinities that can be obtained with antibodies. The higher stability and lower cost of the MIPs nanoparticles makes them however more suitable for integration in membrane processes. 3 patent applications have been filed on this subject. For the actual binding of the MIPs to the membranes, an atmospheric pressure plasma process was developed which generates carboxylic groups at the surface of membranes including the internal pore walls. Several methods to attach the MIPs to the functionalized membranes were investigated and a method based on covalent attachment was selected and developed further for the immobilization of bio-selective MIPs onto microfiltration membranes. Binding affinities and stability of the attached MIPs were then assessed and information on the capacity of the MIP-functionalised membranes and the regeneration needs could be obtained. The prototype membranes for lab based testing on a small scale proofed successful in retaining micropollutants such as diclofenac, metoprolol, vancomycin and endotoxins. Also regeneration of MIPs surfaces was successfully demonstrated. In addition to the MIP-functionalized membranes, also charged polyethersulfone (PES) membranes showing a high retention of viruses based on charge interactions were developed.
The technological developments within this project were supported by modelling activities which have resulted in an enhanced principle understanding of water purification processes using a multi-scale approach, from the nano- to the meso-scale, allowing also the virtual generation of membrane geometries. In addition, a flexible decision support system, which includes quality and measures, has been developed for finding the best possible compromises between cost and performance of membrane synthesis and membrane processing.
The Environmental, Health and Safety (EHS) aspects and the Life Cycle (LCA) of the newly developed materials and technological routes have been carefully assessed and published.

Potential Impact:
During the last few decades, the drinking water industry has become increasingly concerned about the occurrence of micropollutants in source waters for drinking water supply. Also the need to remove viruses from potable and agricultural water supply is long recognized. According to the World Health Organization more than 3 billion cases per year of diarrhea disease occurring worldwide can be attributed to unsafe water supplies, resulting in more than 1.8 million deaths per year, primarily infants and children in developing countries.
Today, membrane processes mainly rely on size exclusion and the pores of filtration membrane used for removal of micropollutants and viruses are very narrow which translates into very limited water fluxes. This means that filtration processes are not efficient as they could be, and with society’s growing needs for fresh water and increased water scarcity, these limitations can become a problem.
Therefore, the integration of research efforts carried out in this project was targeting enhanced membrane performance with respect to permeability and flux in combination with enhanced separation functionality of membranes for the removal of micropollutants and viruses from sources of drinking water. For this aim, nano-structured, low-fouling ultrafiltration (UF) membranes have been developed by bottom-up synthesis for a better control of porosity, pore size distribution, hierarchical orientation of the pores, surface roughness and surface energy. Simultaneously, ligands for supramolecular recognition, in particular ‘Molecularly Imprinted Polymers’ (MIPs) have been developed and immobilized onto newly developed microfiltration (MF) membranes for effective capture of viruses and micropollultants. The introduction of highly selective affinity sites at the membrane surface allowed a more efficient removal of micropollutants with the prospect of operating the newly developed adsorber membranes at pressures much lower than those applied in nanofiltration (NF) or Reverse Osmosis (RO) filtration. In order to reach the above mentioned project outcomes, innovative fluoropolymer and sulfone polymer materials for membrane manufacturing were developed with possible spillovers in other application areas. Furthermore, innovative, atmospheric plasma based post-treatments of membranes were developed in this project to add functionality to polymeric membranes.
The combined use of the nano-structured low-fouling UF membrane and the MF membrane functionalized with affinity ligands should allow the production of safe drinking and process water, both in Point of Use (POU) or Point of Entry (POE) applications, with much lower energy consumption than state-of-the-art membrane processes.
The RTD activities carried out in this project have resulted in a number of dissemination activities including 10 peer reviewed papers, 4 of which are still in preparation, 20 oral and 20 poster presentations at conferences. The NANOPUR project also took up a leading role in the NANO4WATER cluster (https://nano4water.vito.be/) which was initiated to facilitate dissemination and information exchange between the projects dealing with the application of nanotechnology for water treatment. VITO coordinated the cluster and established links with other clusters like CHEMWATER and the European Water Platform. Furthermore, the project has resulted in several exploitable results and 5, possibly 6 patent application filings.
One outcome of the project that will be further exploited is related to the newly developed method for the production of Molecularly Imprinted Polymer (MIP) nanoparticles. MIP nanoparticles with very high affinity for micropollutants and viruses, could be synthesized and immobilized onto membranes for removal of these compounds from water. Antibodies are the most common recognition element utilized in affinity capture and they can be raised against most micropollutants with very high binding affinity and specificity. Antibodies are however very expensive and show a lack of stability in the conditions in which the membranes developed within NANOPUR are to be used. Therefore, Molecular Imprinted Polymer (MIP) nanoparticles with very high binding affinity for selected micropollutants and viruses, good stability and possibilities for up-scaling and regeneration can represent a good alternative to antibodies. Moreover, the MIPs cannot only be used in membrane applications for removal of viruses and micropollutants, but also in chromatography and sensor and diagnostics applications.
With respect to the functionalization of membranes with MIPs for the highly selective capture of micropollutants and viruses at high flux, additional research is needed to confirm the potential of the functionalized membranes. The immobilization method should be further optimized and the MIPs production should be scaled-up. Follow-up projects will be defined to tackle these issues.
New copolymers were developed and used as additives in the production of PVDF ultrafiltration membranes. The resulting membranes showed improved structure, filtration performance and antifouling properties, representing a significant progress beyond the state-of-the-art. The application field of the newly developed copolymers reaches however beyond membrane technology and may also bring added value to other materials produced from PVDF like polymer films, non-wovens, fabrics, etc. Partners are being searched for further exploitation of this project result.
A new plasma process for the stable hydrophilization and functionalization of PVDF membranes without affecting the bulk properties of the membrane has been developed. The main innovative feature of this process is related to the water stability of the treatments, which was also successfully demonstrated during long-term pilot-tests. The process is ready for industrial application and is not only applicable to membranes but to fluorinated polymeric materials and polysulfones in general, including films, non-wovens, yarns, foams and even powders. Further optimization and implementation is ongoing via bilateral collaboration with project partners and partners outside the project consortium.
Another project results closely related to the new plasma process is the new electrode concept for existing atmospheric plasma equipment that was developed to ensure surface hydrophilization and functionalization across the whole cross section of a membrane and not just on its surface. The new hard-ware module is not only applicable for treatment of membranes but also for homogeneous in-depth plasma treatment of porous materials in general (non-wovens, fabrics, etc.).
The hydrophilized PVDF membranes that can be produced applying the above mentioned method and hardware have been produced at pilot-scale and are ready for commercialization on the short term by one of the project partners after the in-line implementation of the plasma equipment.
The modelling activities within the project have resulted in a model to predict membrane performance and to allow optimization of membrane morphology and flow parameters. In addition, a decision support system for the rational design of membranes and related processes has been developed to identify the best possible compromises between cost and performance. This knowledge will be transferred to interested parties via bilateral collaborations or consultancy services.

List of Websites:
https://nanopur.vito.be
https://nano4water.vito.be/
Contact person:
Sabine Paulussen
VITO
Boeretang 200, 2400 Mol, Belgium
Sabine.paulussen@vito.be
0032 492 58 61 25