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Development of intensified water treatment concepts by integrating nano- and membrane technologies

Periodic Report Summary - NAMETECH (Development of intensified water treatment concepts by integrating nano- and membrane technologies)

Project context and objectives:

At European level, a number of relevant research activities have been funded by the European Commission (EC) in the scope of the Seventh Framework Programme (FP7) concerning the application of nanotechnology for water treatment. In detail, the nano4water cluster (please see http://nano4water.eu/ online) comprises five collaborative projects cofounded by the Research DG of the EC following a joint call on nanotechnologies for water treatment (FP7-ENVNMP-2008-2), plus one project funded under the Sixth Framework Programme (FP6). The aim of this action is to support research and technological development (RTD) in the field of water treatment by applying developed or adapted engineered nanomaterials to promising separation, purification and detoxification technologies. The projects of the nano4water cluster focus on two approaches aiming to improve efficient water treatment:
- the development of nanomembranes, where engineered nanomaterials are incorporated into the membrane matrix or are deposited on membrane surface; and
- the use of nanomaterials in catalytic reactors in order to accelerate degradation reactions.
With regard to production of nanomembranes, the EC-funded NAMETECH project (Grant Agreement No. 226791) harnesses benefits of nanotechnology to bring about improvements in membrane filtration for advanced water treatment. The NAMETECH consortium, led by the Flemish Institute for Technological Research (VITO, please see http://www.vito.be online), comprises high level industrial partners, such as Norit Process Technology B.V. and Suez Environment - CIRSEE.

The general objective of the NAMETECH project is to strengthen the European membrane market by making nanotechnology available to large scale European membrane manufactures. The project brings together all required elements to enable the transfer of nanotechnology towards the field of water treatment, not just to laboratory scale testing but really reaching the commercialisation stage.

The specific objectives are to adapt and alter physical and chemical properties of nanomaterials (e.g. particle size, surface chemistry, etc.) so that the nanoparticles can successfully be deposited or incorporated in or on membranes, preparing nanoactivated membranes (NAMs).

The second objective is to evaluate the NAMs in the field of water treatment, i.e. separation, purification and / or detoxification. This will be pursued along different technology paths, each targeting different aspects of the water treatment process. In the first technology path, the main objective is to study and compare the various technologies to incorporate some nanomaterials into the membrane structure or on the membrane surface, reducing membrane fouling and thereby enhancing flux. In the second and third technology path, the focus is on the removal of micro-pollutants and detoxification on the basis of different membrane structure, which will be further elaborated later. The envisaged applications for the NAMs can be both ultrafiltration (UF) for treatment of highly and lowly loaded streams (membrane bioreactors, drinking water production, wastewater treatment applications), and nanofiltration (NF) membranes with improved disinfection or micropollutant removal capabilities.

The NAMETECH project is structured in eight work packages (WPs). The various WPs are combined in such way that they systematically harness the benefits of nano-structured materials to bring macroscale improvements in the application of membrane filtration for water treatment.

The project started 1 June 1 2009 and runs for 36 months. Currently, the first 18 months of the project are finished.

Project results:

The primary focus for the first 18 month period has been on WP1 - Selection of nanoparticles. This WP has set up a bridge between researchers who are actively involved in nanoparticle technology and surface modification techniques and those who are active in membrane development. Ad hoc criteria for identification of nanoparticles that can be used for the synthesis of NAMs for water treatment applications are developed. These criteria are:
(1) the functionality of the nanoparticles;
(2) the compatibility of the nanoparticles with UF / PES (polyethersulfone) membranes;
(3) the toxicity of the nanoparticles (task also integrated in WP6); and
(4) the impact of the building-in mechanism for the nanoparticles on mechanical and chemical formation / production of the membranes.
Based on these criteria, Ag, TiO2 and biomagnetite are selected as most promising nanoparticles and dispersions are made. Based on technical and economical discussion, low cost commercially available nanoparticles like ZrO2 are added to this selection.

In WP2 - Nanoparticles deposition, coating techniques for nanoparticles onto the membrane itself or onto the backbone of the membrane are developed and tested. The deposition technologies that are evaluated are layer-by-layer techniques (Ag, Ag+biomagnetite), electrostatic deposition (TiO2), Pd-biomagnetite coating and electrospinning (Ag). All produced membranes are characterised. From all tested technologies, the techniques that have shown the most potential are the deposition of silver nanoparticles through layer-by-layer techniques, the use of biomagnetite and the electrostatic deposition of titania. These techniques will be used during the coming year to synthesise membranes for further laboratory and pilot tests (WP4 and WP5).

WP3 - Mixed matrix membranes is focused on the development of innovative membrane casting methods, identifying compounds able to keep the nanoparticles stabilised in the membrane casting solution, as well as able to ensure compatibility with all membrane components. In this WP, techniques to incorporate nanoparticles inside the membrane matrix are developed. For the preparation of silver containing mixed-matrix membranes, different pathways are followed all starting from the dispersions made within WP1. Both silver nano-colloids and silver salts (silver behenate and silver benzotriazole) are used. Although the synthesis of silver containing mixed-matrix membranes was successful, the properties of the developed membranes are not ideal. The silver release was either too fast (silver nano-colloids) or too slow (silver salts). Therefore, new dispersions of more soluble silver salts in NEP have to be developed within the next months. Besides the silver containing mixed-matrix membranes, membranes including biomagnetite nanoparticles are developed successfully and experiments are performed on the development of polysulfone membranes comprising nano-ZrO2 particles.

In WP4 - Membrane performance testing, the modified membranes developed in WP2 and WP3 are tested at laboratory module scale in order to assess the filtration performance in terms of permeability and fouling propensity, and to understand the impact of the added functionality of the modified membranes on filtration performance. To characterise the antibacterial properties of the modified membranes, two methods are used:
- respiration activity monitoring system (RAMOS); and
- counting colony forming units on agar plates.
The best antibacterial results are achieved with the polyelectrolyte-modified membranes with Ag(0) in the layers. On these membranes, also sludge supernatant-short-term filtration tests are performed. These tests showed that permeate quality is improving by increasing the number of deposited layers, which means that tailored-made membranes can be made for particular applications. Biomagnetite and Pd-functionalised biomagnetite membranes are tested for the removal of azo-dye end Cr(VI) from solution. It is proved that even the low amount of biomagnetite present in the Zirfon-biomagnetite membranes have positive effects on contaminant removal. During the next six months, membranes with a higher amount of biomagnetite will be developed and tested.

In WP5 - Application concept design and testing, modifications needed to develop or improve the membrane module design are identified. In most cases, the incorporation of nanoparticles into membranes leads only to slight changes of concept. Only for the use of TiO2, more rigorous changes of the membrane concept are required. As a next step, the production of pilot scale modules was started. For antifouling applications, ultrafiltration membranes with Ag-behenate and microfiltration membranes with Ag-benzotriazole are produced and tested in a pilot installation. Further tests will be performed on membranes with better soluble silver salts and membranes developed in WP2. As a commercial pathway towards possible exploitation, the shower heads including membranes with silver will be produced and tested.

Technology and impact assessment are carried out in WP6. The toxicity of the nanoparticles is taken into account for the selection of nanoparticles. The next few months, a life cycle assessment (LCA) approach will be used to evaluate the potential environmental impacts of specific nano-based applications and to estimate possible nanoparticle release from modified membranes.

Finally, WP7 is dedicated to dissemination and exploitation activities that are targeted to broaden the possible application field and to economically assess the business opportunities for the newly developed membranes. Main activities performed during the first 18 months of the project are the production of the NAMETECH website and the joint dissemination event of all nano4water cluster projects.

Potential impact:

At the end of the project, the expectation is to have one or more nano-activated membranes and improved membrane concepts available which can be used for the production of drinking water and/or process water. The functionalisation of the membrane has to lead to decreased operational costs thanks to reduced fouling or reduced disinfection post treatment. The expected impact for the industrial partners involved in the project is to improve the market share of European membrane manufacturers and to enlarge the application field.

List of websites: http://www.nametech.eu