Final Report Summary - LBLBRANE (Regenerable active polyelectrolyte nanofiltration membranes for water reuse and metal/acid recovery)
Executive Summary:
The shortage of drinking water in many regions on the planet, including parts of Europe, constitutes a real problem of increasing importance in a world with a growing population. In fact, the use of seawater, brackish water and wastewater for human consumption is becoming a viable alternative to pursue for the future. For this scope the development of novel, competitive and efficient membrane-based reclamation technologies is thus of paramount importance and requires the design and development of novel materials with improved performance and adjustable to the respective reuse applications.
Membrane processes have become a key component in water reclamation schemes due to the possibility to provide high quality water from membrane bioreactors or desalted water from nanofiltration (NF) or reverse osmosis (RO). In spite of the success of membrane technology, membrane separation systems suffer from a serious problem: membrane fouling. Membrane fouling due to plugging by solid particles or by large solutes is a quasi irreversible process and standard cleaning methods cannot recover the initial hydraulic permeability, unless operated at higher pressure. The downside of such measures is inevitably an increase in operation and maintenance costs as well as an adverse effect on the lifespan of the membrane, which is the reason why the whole concept of membrane processes should be revisited.
The general objective of LbLBRANE, scientific as well as industrial exploitation, is ultimately to strengthen the European membrane market by making nanotechnology available to large scale European membrane manufacturers and to provide nanotechnology-based solutions to end users. LbLBRANE is above all an ambitious AND realistic concept; promoting an innovative and promising cheap and green technology for the development of a novel membrane technology. Our focus is on membranes with superior combination of quality, performance, lifespan and competitive price compared to commercially available ones; our ultimate goal would be the production of a regenerable membrane. In order to successfully achieve all these goals, LbLBRANE has been structured in such a way that it covers a wide range of activities from the technology of membrane modification, through to structural module design, life cycle assessment, life cycle costing, nanosafety issues, pilot plant testing by end-users which has the capability to test, exploit, market and distribute the end product. A unique feature of LbLBRANE is having an expert team of world leading academic researchers from universities and research institutes working in close collaborations with leading industrial partners, SMEs and industries, ensuring competent input right from the membrane concept down to lab-scale production and optimisation before scaling-up in pilot plants for end users.
Project Context and Objectives:
The LbLBRANE project aims at applying a simple and powerful method, namely the “so-called” Layer-by-Layer (LbL) technology, to develop a versatile and generic procedure for the fast fabrication of low-cost, stable, chemical-resistant polyelectrolyte membranes. The focus is towards the realization of membranes which could be regenerated in-situ under mild and environmentally friendly conditions and with extremely high permselectivity and mechanical robustness. The ultimate aim is towards implementation of LbL on large-scale, from module design and construction to end-users, especially for water reuse and metal/acid recovery.
The concept is to use the LbL technology to modify the surface of membranes to create a thin active layer for high permselectivity. The LbL technology consists of the sequential deposition of polyelectrolytes on a surface in a precise and controlled manner. The challenge being whether the layers stay on the membrane after deposition and more importantly, are not washed away during filtration or (physical or chemical) standard cleaning procedures. LbLBRANE covers both polymeric as well as ceramic membranes, both very different in the material types, geometries but also pore sizes, ranging from microfiltration to nanofiltration. The use of nanomaterials have also been considered to enhance deposition and/or as a reinforcement of the mechanical properties of the membranes. With the use of the LbL lego-type approach, different architectures of layers are foreseen whereby one can envision a new type of membrane where the top fouled layers could be eroded by chemical treatment and more layers generated in-situ.
In order to achieve such ambitious goals, the consortium of LbLBRANE (visit us at http://www.lblbrane.eu) is composed of 6 universities with world-leading reputation on the LbL technology, 5 SMEs and one company that is Europe’s No. 1 polymeric membrane producer. The description of work (DOW) of LbLBRANE to fit the timing of the work plan is organized in various work packages (WP), led by a WP leader expert in the task assigned to that WP. Briefly, the scientific investigations are undertaken in “LbL technology for membrane modification” (WP1), “Microscopic characterization of membranes” (WP2), “Modelling of PEM membranes” (WP3), and “Macroscopic characterization of membranes” (WP4). “Upscaling: from membrane to module” (WP5) and “Pilot Work” (WP6) take care of the industrial requirements while working closely with “Nanosafety and Life Cycle Assessment” (WP7) to assess the environmental impact of the developed technologies. “Dissemination and exploitation” (WP8) and “Management” (WP9) ensures proper running of the project with emphasis on visibility and exploitation of results towards the design of a commercial concept.
LbLBRANE – a 3-year EU-funded project under the 7th Framework Programme (Grant agreement no. 281047) started in February 2012. In an early stage of the project the piloting could be started. The plants were already equipped with full size modules and the results were very promising. Further developments and stability test were performed and thus XFLOW entered the market with a product for drinking water production. It is a membrane that is able to remove colour and other organic substances but keeps the salt balance rather constant which is desired in drinking water production from surface water. Furthermore the project focused on denser membranes with the ability to retain bi-valent ions to 95 % and micro pollutants to a high degree. The results we achieved suggest that membranes based on LbL technique are competitive towards classical nanofiltration membranes. Hereby the LbL membrane has two major advantages towards the classical nanofiltration membrane. 1. During the production no organic solvents such as hexane, as it is used for the production of classical nanofiltration membranes, are required since the LbL film is prepared from aqueous solutions. 2. The LbL-based membrane is ready for effective cleaning strategies involving hypochlorite and backwashing, both not applicable on classical nanofiltration membranes. With these important advantages we are looking forward to more LbL-based membrane products from XFLOW.
For the ceramic membranes the work was focused on regenerable nanofiltration membranes. The pores of the applied ceramic support were much bigger as compared to the polymeric membranes making a LbL coating rather difficult. However, we were able to cover the pore and to produce a ceramic membrane with a LbL coating on top that retained bi-valent ions to 70 %. Also the regenerabilty was developed. By adding cationic surfactants and/or high concentrated salt solutions the LbL film can be removed before a new LbL film can be assembled making these membranes regenerable. The procedure can be repeated as often as desired without any performance loss. The main drawback of using a ceramic membrane as solely a support material for the LbL technology is the higher costs for the ceramic material if compared to a polymer support. Therefore, without a significant advantage in terms of pressure normalized productivity per square meter membrane area it will be difficult for this type of LbL membranes to commercially compete with classical polymer based nanofiltration membranes. Nevertheless, this type of LbL membranes are very stable and could, by making use of LbL (top-) layer regeneration, be implemented in applications or niche markets were harsh operating conditions occur.
Project Results:
WP 1 LbL Technology for membrane modification (M1-M30)
WP1 was dedicated to the use of the Layer-by-Layer (LbL) technique for the preparation of competitive, efficient and regenerable LbL-modified membranes for water treatment. The work was focused on the deposition of an active (Tasks 1.1 and 1.2) and regenerable (Task 1.4) separation layer made of polyelectrolyte multilayers (PEMs) and an intermediate reinforcing layer (Task 1.3) on model, membrane-like and membrane surfaces. In fact, it was possible to develop a sole LbL-separation layer combining the following properties: high retention of MgSO4 coupled with good flow, stability against standard cleaning and regenerability.
Task 1.1 Film formation and growth on membrane support (M1-M24)
Task Leader: CNRS; Contributors: CIC, ULEI
Brief summary of achievements during M1-M18
The membrane-like surfaces were initiated and developed
Homogeneous LbL deposition on model and membrane-like surfaces was achieved
LbL-film composition and deposition conditions were optimized to achieve the desired membrane properties
Optimum criteria for generating polyelectrolyte multilayers atop membranes were delivered in a general protocol
Achievements during M19-M24
As film growth and homogeneity were similar on model and membrane-like surfaces at the same preparation conditions, the effect of deposition and rinsing time on PEM properties (flux and selectivity) was studied by CNRS and XFLOW on LbL-modified hollow fiber (HF) membranes (XFLOW). Surprisingly, a major acceleration of the deposition and rinsing time by a factor five did allow maintaining the excellent properties of the polyelectrolyte separation layer. While the retention towards MgSO4 was similar for a deposition time of 3 min and 15 min, the flux measured was slightly higher for 3 min.
It was found that a minimum thickness of 17 nm for the separation layer PEI(PSS/PDADMAC)4PSS improved the retention towards MgSO4 from 5.9 ± 2.3 % (uncoated membrane) to 84.6 ± 1.9 % keeping the flux reasonable. Addition of extra layers only decreases slightly the flux without improving the retention of MgSO4. Deposition of the separation layer on a porous intermediate layer and not directly on the porous polymeric membrane avoids blocking membrane pores and allows reaching simultaneously high flux and high retention (Task 1.3).
SURF coated 490 different LbL films (M18-M36: 270) on XFLOW membranes and varied most possible parameters. The results on retention of MgSO4 and on permeability were measured by XFLOW. Most important parameter was the polyelectrolyte type. PAH/PSS yielded the best performance but due to instability against NaOCl the parameter screening in the second reporting period was concentrated to more stable PDADMAC/PSS coating. For PDADMAC/PSS coatings the permeability decreases until the 6th layer. For further layers the permeability is almost constant independent of outermost layer charge. Retention strongly increases after the 5th layer (threshold). There is a clear Odd-Even effect; when the outermost layer is positive, the retention becomes smaller. Higher pressure during coating in cross flow until 3 bar results in a significant increase in retention but a decrease in the permeability. Further minor effects were observed for polyelectrolyte concentration, coating time, coating temperature, annealing after coating and ion strength of washing solution.
Task 1.2 Comparison of the LbL deposition methods (M7-M18)
Task Leader: CNRS
Brief summary of achievements during M7-M18
Characterization of homogeneous PEM build-up on model and membrane-like surfaces using different deposition methods (dipping, spray-assisted and spin-assisted assembly)
Build-up of CNT-based films by dipping on model surfaces
Achievements during M19-M36
Even if spray-assisted and spin-assisted assembly cannot be used for functionalizing the internal surface of hollow fibres, more experiments were carried out by spray-assisted assembly to study the effect of the deposition and rinsing time and the number of layer pairs on the PEM properties. In addition, homogeneous carbon nanotubes (CNT)-based films were successfully prepared by spin-assisted assembly on model surfaces to investigate the effect of in-plane orientation of CNTs on mechanical properties of the reinforcing layer as a function of the preparation methods.
Task 1.3 Evaluation and optimization of the intermediate reinforcing layer (M7-M24)
Task Leader: CIC; Contributors: CNRS, ULEI
Brief summary of achievements during M7-M18
Preparation of stable suspensions of single and multiwalled CNTs
Optimization of the LbL-assembly of CNT-based films on model surfaces
Achievements during M19-M24 (or M36)
Following the results obtained on model and membrane-like surfaces, an intermediate reinforcing layer made of CNTs was built by static coating in hollow fibres (XFLOW) by CNRS and by dipping and solvent evaporation on flat ceramic membranes (LIQ) by CIC to investigate its impact on membrane properties (flux, retention and mechanical resistance) as a function of thickness, composition and architecture. For HF membranes, the addition of an intermediate layer composed of one layer of CNTs between the separation layer and the membrane surface increases already the flux by 30% without changing the retention value (around 85 %) compared to the system without an intermediate layer. Addition of extra CNT layers will increase the porous mesh structure of the intermediate layer and should still improve the flux (measurements by XFLOW in progress). In addition, the CNT reinforcement of PEMs leads to highly interesting mechanical properties (improvement of the Young’s modulus by a factor of 4).
Task 1.4 Film deconstruction and reconstruction for regenerable membranes (M13–M30)
Task Leader: ULEI; Contributors: CIC, CNRS, SURF
Brief summary of achievements during M13-M18
Protocols using surfactant, salt and pH were developed to remove PEMs partially or totally on model surfaces
PEM could be removed partially or totally and rebuilt several times
Achievements during M19-M30 (or M36)
Several subsequent deconstruction/reconstruction cycles for PDADMAC/PSS and PEI/PSS films were achieved on membranes-like surfaces by CNRS and in modules containing polymeric (XFLOW) and ceramic (LIQ and RWB) membranes by CNRS and SURF.
Prior to study the regenerabilty of PEMs in hollow fibre modules, the deconstruction protocol of PDADMAC/PSS films using 3 or 5 M of NaCl was first validated by CNRS on membrane-like surfaces. Then, regenerability of the PDADMAC/PSS film on the internal surface of hollow fibers was confirmed by measuring the flux and retention towards MgSO4 during deconstruction/ reconstruction cycles.
It was found that a residual film thickness corresponding probably to PEI/PSS complexes remains on hollow fibres after deconstruction. Thus, the measured flux after reconstruction of the PEM was slightly lower while the retention of MgSO4 was slightly higher.
In the meantime, SURF’s microscopic investigations showed that PEI/PSS coatings can be removed from LIQ SiC discs by treatment with NaOH solution at pH 12 at room temperature as evidenced by tracking of fluorescently-labeled PEI via confocal laser scanning microscopy. Although removal of PEI/PSS coatings with the relatively mild treatment of high pH is a promising method, the use of PEI/PSS coatings was discontinued in further stages of this project due to their instability against NaOCl, a cleaning chemical that is routinely used in membrane technology.
SURF further performed successful deconstruction/reconstruction of PDADMAC/PSS coatings on LIQ and RWB tubular ceramic membranes as presented in WP5 while CIC performed fouling experiments together with deconstruction/reconstruction cycles (also in WP5).
WP 2 Microscopic characterisation of membranes (M1-M30)
Task 2.1 Structural characterisation of PEM and nanomaterial (M1-M18)
Task Leader: CIC; Contributors: CNRS, ULEI
Brief summary of achievements during M1-M18
The topology of the supporting nanofiltration membrane, the PEM, as well as deconstruction and regeneration of the PEM were characterized by AFM.
The 3-d pore structure of nanofiltration membranes was imaged by means of SEM.
Ion Beam Microscopy (IBM) was used to characterize the elemental concentrations and distributions of N, O, S, Na in flat sheet membranes and hollow fibres.
Fluorescence confocal microscopy showed that depending on the molecular weight polyelectrolytes may penetrate into pores.
Achievements during M19-M30
No further work for task 2.1 was conducted.
Task 2.2 Characterising the composition and the interaction between the membrane components and between membrane components and ions (M4-M18)
Task Leader: ULEI; Contributor: CIC
Brief summary of achievements during M4-M18
FTR-IR investigations showed that the average hydrogen bond strength within polyethersulfone flat sheet membrane membranes is less than in free water. This was attributed to the interference of water binding to sulfonate and sulfone groups with cluster formation in bulk water. This finding may explain for the high water permeability through the narrow pores be reduced friction.
Ether, sulfone and sulfonate groups of PES membranes were identified as binding sites for divalent cations. Upon binding, water molecules are released from these sites and the order of the water network inside pores is further destabilized. The presence of the PEM enhances the binding of divalent cations to the active groups at the pore walls, thereby facilitating retention of divalent cations. Monovalent ions bind much less to characteristic groups of the pore walls.
Achievements during M19-M30
The sulfonate groups of the PEM represent binding sites for divalent cations, thereby significantly contributing to the retention of these ionic species.
IBM was used to quantify the retention of sodium and Ca within membranes. While sodium release takes only seconds the release of calcium ions lasts several minutes. These results confirm the large difference in binding behaviour between monovalent and divalent ions.
From our findings follows that it is not only the interaction of ions with the membrane sites in the pores which causes a significant decrease of diffusional transport of ions compared with water, but also at the same time the interference of these sites with the water structure causing an overall decreased hydrogen bond strength near the pore walls. The latter effect facilitates diffusional or maybe even convectional transport of water in nanopores due to increased slipping and reduced cluster size.
Task 2.3 Diffusion studies in PEM using fluorescence confocal techniques (M7-M24)
Task Leader: CIC; Contributors: ULEI, SURF
Brief summary of achievements during M7-M18
A novel approach for measuring the diffusion of dithionite WITHIN PEM´s of a thickness of only few nanometers based on fluorescence quenching of NBD – labelled PAH by dithionite was established. The diffusion of dithionite as a divalent anion with potential binding capacity to primary amines within PEM´s can be regarded as a model system for diffusion of ions within PEM´s with strong ion – PEM interaction.
The quenching rate depends on quencher concentration, layer composition, nature of the top layer and on background electrolyte concentration, BUT in all cases quenching occurs in the timescale of 102 - 103 s. This is a rather slow reaction-diffusion process for a nanoscale system. The intrinsic reaction rate of dithionite with NBD is high; consequently diffusion is the time limiting step. The kinetics of quenching was inconsistent with a classical diffusion process. The slow ion diffusion due to the binding to charged groups in the PEM layer represents a significant add-on for the separation performance of PEM modified membranes over bare nanofiltration membranes.
Achievements during M19-M24 (or M36)
Diffusion of dithionite was measured in PEM`s containing PDA selected by the consortium as a function of pH and a wide range of dithionite concentrations. The dependence of diffusion on pH observes a trend towards increased diffusion at higher pH.
For data analysis theoretical models of anomalous diffusion with various degrees of approximation were developed and applied to data analysis. One of the simplest models which still allowed a complete analytical treatment was that of a time dependent diffusion coefficient corresponding to stretched exponential behaviour.
A large degree of anomaly and the extremely small diffusion coefficient, as well as the pronounced odd-even effect caused by the influence of the top layer on the internal layer structure and layer ion concentration.
A comparison of RWB ceramic, LIQ SiC and XFLOW HFS polymer membranes with confocal laser scanning microscopy using fluorescent reporter molecules showed that smaller pore size of XFLOW membranes restricts the diffusion of polyelectrolytes into the pores, making these membranes ideal for LbL coating. Pores of RWB and LIQ membranes are coated inside to some extent, making pores smaller and significantly decreasing the permeability. RWB pores can be covered on top with PEM after 4 double layers of PDA/PSS but LIQ pores are too large to be covered on top via PEM.
Task 2.4 Assessment of mechanical properties and stability of PEM at the nanoscale (M10-M30)
Task Leader: ULEI; Contributor: CIC
Brief summary of achievements during M10-M18
Measurements of single polyelectrolyte molecule desorption forces from HFS and HFC membranes revealed that the adhesion energy per monomer is of the order of kT. Given the cooperativity of adhesion such energy gain is sufficient to ensure stable PEM layer formation on membrane supports.
Achievements during M19-M30
Young moduli of free-standing PE films depending on composition and carbon NT reinforcement were of the order of a few GPa. Reinforced CNT-based films were stronger but more brittle than polymer-based films. The CNT reinforcement of PEMs leads to highly interesting mechanical properties (improvement of the Young’s modulus by a factor of 4). We also found that these mechanical properties are not affected by the presence of salt during the PEM build-up.
Under normal operating conditions LbL-Films deposited on membranes should be stable toward rupture and spontaneous desorption. Chemical stability during cleaning is a much more critical issue and effectively limits the choice of polyelectrolyte species applicable for industrial nanofiltration devices.
WP 3 Modelling of PEM membranes (M4-M30)
Task 3.1 - Development of random-walk model for the prediction of microscopic mobilities of water and ions with PEM (M4-M18)
Task Leader: ULEI
Brief summary of achievements during M1-M18
Random walk simulations of diffusion in PEM´s were performed in the framework of the Continuous Time Random Walk (CTRW) model with waiting time distributions, the first moment of which has an infinite value corresponding to anomalous diffusion. This reflects the expected strong binding of the diffusing species to specific sites of PEM´s. The fluorescence decay involves also the reaction rate of the quencher with the reporter, which is described as diffusion limited process.
The experimentally observed subdiffusion behaviour in multilayers was alternatively simulated applying a Monte Carlo approach by a superposition of normal diffusion processes with distributed diffusion coefficients.
Achievements during M19-M36
Starting from CTRW simulations with appropriate underlying waiting time distributions it was possible to obtain in a second step relatively complex but analytical solutions, which were the basis for subsequent comparison of the simulated behaviour against experimental results.
Normal diffusion cannot explain the fast initial decay followed by a continuous slowing down of the diffusion process. Dithionite diffusion can very well described with an anomalous behaviour. The physical basis for this slow diffusion is the strong binding of the diffusing ion to two groups of the PEM matrix. It was further observed that ion binding itself modifies the properties of the matrix. The developed models were the basis for the analysis of diffusion data presented in WP2.
Task 3.2 Predicting membrane performance and behavior based on permeability for single ions (UPC)
Brief summary of achievements during M1-M18
Solution-Diffusion-Electro-Migration-Film model was used to obtain general solutions for trans-membrane transfer of electrolyte mixtures containing ions of 2, 3 and 4 different charges.
These solutions were used for detailed parametric analysis of Nanofiltration, Pressure-Retarded Osmosis and Forward Osmosis in multi-ionic solutions.
Achievements during M19-M36
Parametric solution for nanofiltration of 3 ions of different charges and its uses for the exploration of trends in the metal/acid separations
By using the previously obtained transcendental relationship between the total concentration of ions and the total ionic strength in the permeate we derived this parametric analytical solution for the case of 3 ions of different charges
C_p≡C(u_p )=[(G(u_p )-a(u_p )+u_0)/(G(u_p )-a(u_p )+u_p )]^((G(u_p )-a(u_p ))/2G(u_p ) )∙[(G(u_p )+a(u_p )-u_0)/(G(u_p )+a(u_p )-u_p )]^((G(u_p )+a(u_p ))/2G(u_p ) ) (1)
J_v (u_p )=(1/C(u_p ) -1)∙(Z_1-Z_2 )(Z_2-Z_3 )(Z_1-Z_3 )/(Π∙B_(-1)+B_0∙u_p ) (2)
where
a(u_p )≡(Π∙(B_1-Σ∙B_0 )+(B_2-Σ∙B_1 )∙u_p)/2(Π∙B_(-1)+B_0∙u_p ) (3)
G(u_p )≡√(〖a(u_p )〗^2-Π∙(Π∙B_0+B_1∙u_p)/(Π∙B_(-1)+B_0∙u_p )) (4)
B_i≡(Z_1^i∙(Z_2-Z_3 ))/P_1 +(Z_2^i∙(Z_3-Z_1 ))/P_2 +(Z_3^i∙(Z_1-Z_2 ))/P_3 (5)
Π≡Z_1 Z_2 Z_3 (6)
Σ≡Z_1+Z_2 〖+Z〗_3 (7)
P_k is the membrane permeance to the k-th ion, Z_k is the charge of k-th ion, J_v is the trans-membrane volume flow.
Eqs(1,2) provide a parametric relationship between the trans-membrane volume flow and the total ion concentration in the permeate, C_p using the relative double total ionic strength in the permeate, u_p, as the parameter. This relationship has been used to explore trends in the metal/acid separation by PEML membranes. We calculated reciprocal ion passages across PEML membrane with the ion permeances mimicking those of tubular PEML membrane determined by the trace ion method and summarized in the Deliverable 4.4. In these calculations, we have also taken into account concentration polarization and the effect of osmotic counter-pressure on the trans-membrane volume flow. The latter is relevant because in practical metal/acid recovery processes the feed concentrations are usually moderate to high, and the osmotic phenomena are quite important. The calculations showed that PEML can be very efficient in the process with metal/acid selectivities far exceeding 100. They also demonstrated that the situation of prevailing acid is generally beneficial because high metal rejections are reached already at fractions of osmotic pressure.
Task 3.3 CFD modelling of kinetics of membrane cleaning/regeneration in modules (Task Leader: UPC; contributor: RWTH)
No activities during M1-M18
Achievements during M19-M36
In view of the evolution of R&D needs, it has been decided to concentrate on the following modelling issues, which were found to be more important for the optimization of preparation of PEML and their practical application:
- kinetics of deposition of first polyelectrolyte layers on porous supports in view of “over-bridging” of larger pore entrances;
- CFD modelling of external mass transfer in tubular membranes with “decorated” internal surface in developed turbulent flows.
Modelling of kinetics of deposition of first polyelectrolyte layers on porous supports
We simulated numerically the kinetics of deposition of polyelectrolyte macromolecules within the entrance regions of pores of a nano-porous support. Due to the electrostatic repulsion, at each coating stage, the deposition is limited by the formation of one monolayer. Multilayer deposition is possible by subsequent deposition of layers with alternating charges. Deposition process in thin pores is complicated because the diffusivity of particles changes due to hydrodynamic interactions with the pore walls and becomes anisotropic. This effect was accounted for in the modelling. The principal conclusions from this modelling effort are:
Retardation of diffusion due to the macromolecule-wall interaction results in an essentially slower deposition and a thinner deposited layers formation for the same deposition time.
The optimal time of deposition depends on the polyelectrolyte concentration and macromolecule size.
By an increase of time an essentially thicker layer can be formed by 2-layer deposition with larger macromolecules compared to 3-layer deposition with smaller macromolecules.
In quasi-steady regimes the polyelectrolyte deposition takes place at the channel entrance only.
WP 4 Macroscopic characterisation of membranes (M1-M30)
Task 4.1 Characterisation of in-situ LbL assembly (M1-M12)
Task Leader: RWTH; Contributors: CONV, XFLOW, SURF
Brief summary of achievements during M1-M18
Design and build-up of OSMO Inspector designated for LbL coatings (CONV). With this setup first coatings with in-situ measurement of the TMP could be realized (RWTH).
Further measurements with several combinations of different polyelectrolytes, varied layer number, ionic strength, and pH were performed (RWTH, XFLOW, LUT, SURF)
Observation of the “Odd-Even” Effect and explanation by pore/surface dominant regime
Proof of layer presence by elemental analysis (EDX) and optical visualization by SEM (XFLOW, ULEI, RWTH) and degree of penetration into pores by CLSM for all membrane types (SURF)
Achievements during M19-M36
RWTH further focused on in-situ measurement of TMP evolution during coating on both, ceramic and polymeric hollow-fibre membranes. Coatings at different flux and different coating time but with the same amount of polyelectrolyte mass retained at the membrane surface were investigated. While the TMP-rise is a function of coating flux and time, the resistance values coincide on a master curve for both polyelectrolytes. The apparent resistance during filtration scales with the mass of polyelectrolyte that is transported into the lumen of the hollow fibre but is independent of the coating flux or coating time. Also the feed pressure level can be neglected as a potential parameter for the layer build-up since the pressure evolution differs for the coatings at the different flux levels. Possible compressing effects during layer build-up due to the pressure gradient between feed and permeate can thus be excluded.
Task 4.2 Stability of PEM (M1-M18)
Task Leader: RWTH; Contributor: XFLOW, SURF
Brief summary of achievements during M1-M18
Layer stability towards backflushing and crossflow was proven(XFLOW, RWTH, LUT)
First stability test for acid, base and high salt concentration were conducted (XFLOW)
In situ stability test with OSMO Inspector were carried out (RWTH)
Crosslinking of polyelectrolyte improved the salt stability but decreased the overall retention (RWTH, SURF)
Achievements during M19-M36
In order to evaluate the chemical resistance the LbL modified membranes were exposed to acid, base, NaOCl, high salt concentrations and surfactants. The PDADMAC/PSS system is stable to acid (pH 2, XFLOW) and base (pH 11 tested on the polymeric membrane (XFLOW), pH 12.5 tested on the ceramic support (RWTH)). Also NaOCl, a cleaning agent very commonly used in membrane filtration, does not harm the LbL modified membranes. 100 000 ppmh of NaOCl treatment resulted in no degradation (XFLOW, RWTH). However only two of 10 tested polycations were resistant against NaOCl, namely PDADMAC and PVBTMA (SURF). Cationic surfactants, such as CeTAB, DoTAB, and TTAB, were found to be possible candidates to remove the layers (SURF, LUT). In addition the stability towards salt was evaluated (RWTH, LUT). A NaCl solution was filtered through the membrane at a constant flux while the TMP was logged and thus in-situ changes in the layer can be recognized by the layer resistance. At a NaCl concentration of 1 mol/l we observed first changes in resistance which indicate layer destruction. At higher salt concentrations above 3 mol/l, the degradation was much more pronounced. However, the instability towards cationic surfactants and high salt concentration can be used to regenerate the layer. A total regeneration of ceramic and SiC membranes in situ could be achieved by application of oxidizing piranha solutions without degradation of the inorganic membranes (SURF). This is further discussed in WP5. Since PDADMAC/PSS system has a limiting retention of about 90% P2B/PSS was investigated as an alternative polyelectrolyte system (LUT). Unfortunately the P2B/PSS system did not show a sufficient stability to NaOCl and thus was not further investigated.
The stability of the polyelectrolyte film against water filtration as a function of the pressure was performed on ceramic and polymeric membranes by means of CLSM (SURF). No change of the polymer amount and distribution could be found until a pressure difference of 3 bar.
Task 4.3 Evaluation of the membrane performance (M7-M24)
Task Leader: LUT; Contributors: RWTH, CONV, SURF
Brief summary of achievements during M7-M18
LbL modified membranes were evaluated by measuring the retention for MgSO4 and permeability. Properties of nanofiltration membranes with retention for bivalent ions and permeabilities of about 10 LMH/bar were observed (XFLOW, RWTH, LUT, SURF)
XFLOW applied a full scale module with LbL modified membranes for surface water and removed TOC and color for about 60 to 80 % and above 90 % respectively.
Achievements during M19-M36
Several different coating with different layer numbers, different coating fluxes or pressures, varied coating time, and varied salt concentration during coating were applied. All coated membranes were evaluated by measuring the pure water permeability and the retention for MgSO4 (bivalent ions). Some chosen candidates were characterized more in detail by determining the MWCO, and retention for different salts (monovalent, bivalent and mixtures, details can be found in Task 4.4). LUT conducted experiments by using three different polyelectrolyte system: a) PDADMAC/PSS, b) P2B/PSS, and c) PDAMAC/PAA. They found the best retention values for the PDADMAC/PSS system using MgSO4 and PEG. SURF and XFLOW further focussed on the PAH/PSS system with astonishing high retention of about 97 % for MgSO4 and above 90 % for NaCl. However, PAH is unfortunately not stable towards NaOCl. Nevertheless it is at present, by far, the highest retention of an LbL-modified membrane that we observed. This polyelectrolyte pair showed also the best retention for drugs and hormones (XFLOW, SURF). But further investigation on other polyelectrolyte system that yield high retention values with a good stability is necessary. RWTH further investigated the PDADMAC/PSS system. As already observed for the resistance during coating (Task 4.1) the properties of the resulting membranes depend only on the mass of polyelectrolyte retained in front of the membrane surface. That means that we can aim for target properties and obtain them through different fabrication conditions. Hence it proves, for the first time, how precisely the method allows to engineer desired pure water permeabilities and retention properties.
XFLOW conducted some work on protein adsorption and fouling. They measured the adsorption of BSA on PDADMAC and on zwitterionic polyelectrolytes such as PSBMA and PSBMA-AA. Both, the adsorption measured with ellipsometry on silicon wafers and the permeability decrease during BSA filtration, was less when using PSBMA or PSBMA-AA instead of PDADMAC as the terminating layer.
Task 4.4 Characterisation of ion rejection (M10-M27)
Task Leader: UPC; Contributors: CONV, SURF
Subtask 4.4.1 Adjusting experimental set-ups (UPC, CONV)
Brief summary of achievements during M1-M18
The set-up for the electrochemical concentration-step technique was modified to implement liquid delivery by a computer-steered syringe pump; the software was upgraded to make possible fully automatic data acquisition.
CFD simulations demonstrated that the originally planned configuration of a batch cell with a disk-like stirrer put on a hollow axis does not provide equally-accessible membrane surface.
CFD simulations revealed that in an alternative configuration of a rotating disk-like membrane the membrane surface is equally-accessible apart from a narrow membrane periphery that can be excluded from the filtration.
Based on this, a prototype of rotating-membrane test cell was designed, built and preliminary tested
Achievements during M19-M36
UPC developed one more test-cell design with equally accessible membrane surface, namely, developed turbulent cross-flow with discarded permeate from the entrance zone as described in D4.4.
In the concentration-step setup, a special mask was developed to limit the propagation of drop of non-equilibrium solution after the concentration step. This has considerably improved the signal reproducibility. Extensive measurements of transient membrane potential after concentration step performed for a lab-made polymeric support (provided by Pentair-X-Flow) coated with a variable number of bi-layers of PSS/PAH revealed an interesting feature of non-monotone dependence of signal on the number of bi-layers. Besides, they exhibited a relatively good reproducibility that improved with increasing number of bi-layers. We suppose this to be caused by the improving homogeneity of membrane surface properties with the progress in coating.
Subtask 4.4.2 Measurement of ion rejection (UPC)
Brief summary of achievements during M1-M18
First measurements of transient membrane potential after concentration step revealed clear correlations between the signal and the state of the surface (PEML coating).
Achievements during M19-M36
The turbulent cross-flow setup was employed to obtain experimental data by means of trace-ion method. These data were used for the calculation of ionic permeances reported in the database of D4.4. The rotating-disk setup suffered from leaks for some time but finally could be improved to provide reproducible data with commercial NF membranes (no leaks). In the case of PEML membranes, there still appear to occur some leaks supposedly related to a PEML damage by the membrane-sealing O-ring. Indeed, the rejection of Mg2+ was practically independent of trans-membrane volume flux and exceeds 97%. This made us believe that the Mg2+ rejection by the intact PEML was actually still much higher and the pressure-independent relative passage of ca.2.7% of Mg2+ was due to a leak caused by the PEML damage. Our measurements also revealed a considerable dependence of MgCl2 rejection on the type of support when using the same polyelectrolytes (and deposition procedure). With the tubular support the MgCl2 rejections did not surpass 80% whereas with the flat-sheet support it exceeded 97% and was probably still much higher (see above). The membrane hydraulic permeability was ca.2 times lower with the flat-sheet support. This may point to a denser PEML, which could also cause a higher rejection although the difference in the rejections is much more pronounced than in the permeabilitites.
WP 5 Upscaling: from membrane to module (M10-M30)
Task Leader: LUT; Contributors: RWTH, CIC, RWB, CONV, XFLOW, ULEI, SURF, LIQ
This WP aims to solve possible problems arising from scaling up from single membranes to full or semi-full scale modules:
designing of modules for in-situ LbL deposition
optimising protocol for best LbL deposition conditions inside modules
assessing performance of regenerable modules
This WP has been divided into three Tasks (Adapting module design and construction, Coating and regeneration process inside modules and Proof of concept – performance assessment) of which in Task 5.2 the most up-scaling work was planned to do (Sub-tasks Lab-scale module and Operational-scale module).
Task 5.1 Adapting module design and construction (M10-M18)
This Task is devoted to make changes needed and redesign existing modules and housings to enable LbL depositions inside modules. Different designs may be needed for lab-scale testing than for upscaled modules as well as the possibility to remove and reconstruct polyelectrolyte layers was to be taken into account.
Brief summary of achievements during M10-M18
Scaling work was actually started in WP4 by coating single fibres or very small (short) ceramic modules. Basic knowledge of coating on single fibre module (experience gained in WP4) was successfully transferred to modules containing several fibres and coating of several modules at the same time. Upscaling of polymeric modules was successfully done and full-scale commercial elements were LbL coated by XFLOW. Same work with ceramic modules turned out to be somewhat slower but coating protocol was created for them in semi-full scale modules. Coating itself could be performed in all sizes but LbL coated ceramic membrane performance was not satisfactory (even in small scale) due to their inherent macroscopic pores.
Achievements during M19-M36
Al2O3 ceramics (RWB)
Due to the too low in-field evaluated permeability (i.e. L/(m2*h*bar)), final design is a R&D scale- NF membrane module (0.04 m2, ceramic based) with an open feed structure. Two module types were designed, resulting in a broad application range tuned to the desired- operating and (chemical-) resistance conditions.
Type II was successfully used for lab-scale (in-situ-) regeneration experiments (see Task 5.2). Module design implemented allows for direct upscaling to a (small-) commercial scale: 0.4 m2.
SiC ceramic membranes (LUT, CIC, LIQ, SURF):
The module geometry and its active area were changed for the last coating experiments utilising CNT reinforcement layer prior to LbL layers. LIQ sent 40 nm pore diameter, 1 channel, L 250 mm, ID 6.0 mm membrane modules to CIC who coated them with a CNT layer using facilities of SURF. Then these CNT coated SiC monotubes were shipped to LUT who coated them with LbL layers and performed the usual tests using LIQ housing build for these monotubes. The SiC module was shifted to smaller monotubes due to limited amount of CNT solution. This way more modules could be tested with CNT reinforcing layer.
Task 5.2 Coating and regeneration process inside modules (M13-M24)
This task investigates different parameters to construct optimized LbL coating inside modules first in small scale and then in larger operational scale. Also regeneration of the coating after partial or full removal is studied. Adapted modules from previous task are utilized here. Utilization of CNT layers and other reinforcing substances prior to LbL layers to tighten and smooth out the rather open ceramic membranes was also looked at in this task.
Brief summary of achievements during M13-M18
A set of experiments have been done to look at the possibilities of regeneration. It was found that complete removal of LbL layers from polymeric membrane surface is not possible without destroying the substrate as well. Therefore the strategy with polymeric membranes was shifted and regeneration was not objective anymore (it was also independently found unnecessary too with polymeric membranes, see D5.1). Complete removal of LbL layers from pores of ceramic membranes was found hard as well. However, regeneration on top of incompletely removed LbL system resulted in even better performance than constructing LbL layers on clean pristine ceramic surface, see D5.2. It was found also that after the first regeneration, further LbL layers could be constructed rather reproducible manner.
Achievements during M19-M36)
Lab-scale (SURF, LUT, RWTH)
LIQ and RWB tubular membranes were tested for construction/deconstruction/ reconstruction inside modules (see D5.2)
LIQ tubular membranes were coated with 10 double layers of PDA/PSS. Complete deconstruction of these LbL coated layers is possible by subsequent treatment of membranes with DoTAB and NaCl. The order of application is crucial.
RWB tubular membranes were coated with 6 double layers of PDA/PSS. In contrast to LIQ membranes, DoTAB + NaCl treatment did not result in a complete layer removal
PDA/PSS layers on RWB membranes could be completely removed by a diluted pirahnha solution in module
Recoating of both RWB and LIQ membranes with PDA/PSS layers is possible
PDA/PSS coatings are stable against NaOCl and NaOH solutions
High Salt concentration can be used to destroy the film but the layer will never be removed completely.
LbL coated ceramic membranes with CNT reinforcing layer (LUT, CIC, LIQ, SURF, RWB, RWTH):
Due to relatively poor salt retention performance of only LbL coated ceramic membranes, it was tried to reinforce the substrate prior the LbL coating by carbon nanotube layer (CNT). CNT coating of SiC membranes was done by CIC on LIQ monotube membranes. LbL coating was done normally with a (PDADMAC/PSS)3 system by LUT and tested with dilute MgSO4 solution at neutral pH. Some of the results were very promising since Mg2+ retention increased from about 60% (without CNT layer) up to about 90% (with CNT middle layer) while permeability remained at the same level. However, the stability of the combined CNT+LbL layers was still rather weak since only one trial out of four was successful. RWTH applied CNTs prior to LbL coating on the RWB ceramic membrane. The flux decreased as with LbL coatings only (as a function of bilayers) but remained more than twice higher when a CNT layer was used even after 8 bilayers. This was due to bridging effect of CNT network produced over pore openings preventing PEs to enter deeply inside the pores during the LbL deposition process.
Operational-scale (RWB):
Type II membrane module outlined in Task 5.1 was implemented in the semi-bench scale pilot for continuous testing of the membrane module under high pressure backwash (BW, P = 5 bar) and air flush (i.e. AF, P = 2 bar) conditions.
No active NF top layer deterioration and/or removal were observed. In addition, no sealing-, integrity- or module problems were encountered. (In-situ-) regeneration was not yet executed on an operational scale.
Task 5.3 Proof of concept - performance assessment (M16-M30)
This task is for final testing and evaluation of best performant membranes in labtests and on-site as well and for longer periods of time if possible.
Brief summary of achievements during M16-M18
Due to some small delays in development of LbL membranes on ceramics, the tests with them were not actually started during M16-M18. However, the work with polymeric membranes carried out clearly faster and on-site tests with them were started before M16. The results are reported in WP 6.
Achievements during M19-M30 (or M36)
Within a short labscale pilot study the LbL membranes using different supports were benchmarked and compared with an commercial available nanofiltration spiral wound module (Tests and coating of all applied membranes was done by RWTH). As feed the effluent from a waste water treatment plant equipped with an ultrafiltration unit as the last step was employed. Detailed results are shown in D5.3.
Fouling was more pronounced on the LbL membranes than on the commercial DOW NF270 spiral wound module. This is not really surprising since the spiral wound module is an out-engineered product that has spacers to introduce turbulences that reduce fouling. However, after longer filtration time this membrane would also show a performance loss. And then the tubular LbL membranes would have the advantage of simple cleaning methods like backwashing and NaOCl treatment which are both not applicable on the DOW NF270 spiral wound module.
TOC removal was for all tested membranes comparable. The low TOC reduction of roughly 60 % showed that there are a lot of small organic compounds in the water that can pass all tested membranes.
The rejection for bi-valent anions was the best for the DOW NF270 but also the LbL membranes retained SO42- between 75 – 90 %.
The rejection for bi-valent cations was better for the LbL membranes than for the DOW NF270. The retention on the LbL membranes was even partly higher than the rejection for bi-valent anions which is really surprising and cannot be explained so far.
The small scale pilot study with real waste water showed that the LbL membrane has serious potential to be competitive to real NF products already on the market. Only the rejection of bi-valent anions was significantly higher on the DOW NF270 than on the LbL membranes.
We tested 4 differently coated XFLOW polymeric HFs membranes. One of these membranes had a coating that was done on low flux and only two bi-layers. As expected this membrane had a quite high permeability of roughly 30 LMH and a lower retention for the analysed compounds. It is not always desired to retain everything and therefore the LbL mechanism is optimally suited to prepare membranes that fit the needs of the intended separation process perfectly.
For the long term pilot tests where only the total organic contents of the feed needs to be reduced and electrolytes need to pass the membrane, the coatings presented that are less dense should be suitable. Therefore, for the direct filtration of surface water membranes with 2 and 3 bilayers will be tested in WP 6.
For the pilot test where a denser membrane is needed (e.g. for the removal of low molecular weight organics), the results presented here (by XFLOW) indicate that 2 bilayers will not be sufficient (however, recent results from RWTH show that, with the right coating conditions, quite dense layer could be obtained for even 1 bilayer). For these pilot studies we will therefore opt for denser coating on HFs membrane.
WP 6 Pilot Work (M25-M36)
Task Leader: XFLOW; Contributors: RWTH, RWB, LUT, LIQ
Municipal waste water treatment
Direct sludge filtration (tubular LbL NF) vs. effluent polishing with LbL systems for municipal applications – comparison of conventional UF vs. direct NF. (X-Flow)
Two different experimental set ups are performed for this task.
Direct sludge filtration with a tubular UF and a tubular LbL Membrane.
Effluent polishing of an aerobic membrane bioreactor (a-MBR) equipped with an Ultrafiltration (UF) membrane. UF permeate is treated again with an UF membrane and with three different LbL membranes.
Major Results
Tight LbL membranes remove 50% more organics than comparable UF membranes.
Effluent polishing with LbL coated membranes can remove up to 90% extra color and organics from the effluent.
A T2 membrane is an excellent candidate to remove organics without changing the salt balance dramatically.
LbL coating membranes is a perfect toolbox to produce tailor made membranes for the wishes and demands of the customer.
Comparison of a MF/NF270Dow vs. MF/NF LbL (MBR effluent polishing, focus on micropollutant tests) RWTH
This benchmark study was conducted by filtering effluent from a waste water treatment plant (Kaarst) with different membrane modules for one week. The waste water treatment plant is equipped with ultrafiltration membranes as the last step before the water is pumped to a river.
Major Results
Commercially available NF (DOW NF270) membrane performs better in terms of micro pollutant retention. In this research we focused on a polyelectrolyte system (PDADMAC/PSS) that is chlorine resistant (WP2, 4 and 5), a unique feature that the current NF membranes on the market does not have. Therefore the LbL membranes can be easily cleaned to ensure long term stability, knowing that the achieved membranes are not as dense as other LbL systems.
Achievements during M19-M36
Direct sludge filtration with LbL-coated membranes is possible and color retention is superior.
Effluent polishing with LbL-coated membranes can achieve directly dischargeable water.
The retention of the LbL system PDADMAC/PSS on micropollutants is inferior compared to commercial nanofiltration membranes.
Drinking water production
Drinking water production (non-chemicals, direct discharge, no pre-treatment). [RWB]
In total, two pilot test trails were executed with canal water (i.e. surface water). Both test trails were completed within the stated time frame (M25 – M36) without delays.
Application : drinking water production;
Feed water : canal water, Twentekanaal, Bornebroek, The Netherlands (NL);
Module : ceramic based LbL membrane module, active NF top layer (0,04 m2);
Concept : main concept features can be summarised as:
(1) direct intake without addition of chemicals to the feed water, (2) open feed module structure for suspended solid (SS) as well as partial ion removal (3) total treatment step reduction;
Outcome : obtained in-field permeability is limiting, resulting in too high system costs.
Major results
Although the concept looks promising in terms of treatment step reduction-, chemical reduction- and obtained water properties (i.e. permeate-), the final outcome of the concept proposed is judged negative. This negative outcome is primarily determined by the obtained membrane performance (i.e. evaluated in-field permeability), resulting in too high costs for the total treatment system.
Drinking water production (X-Flow)
Pilot Test (8”module) Yorkshire Water (UK) – direct THM precursor removal
An 8” inch (full scale) module coated was coated with 2 bilayers of PDADMAC/PSS and tested in a full scale pilot installation.The pilot plant operates semi-automatically, with a system to control the feed flow and pressure.
Major Results
In the initial stages of the experiments, the LbL membrane outperformed the current rapid gravity filters (RGF) on the removal of THM precursors (THM-Formation Potential). However, after roughly two months of operation, a change is observed. The significant increase in THM-FP levels in the membrane permeate, were also accompanied by an increase in the DOC levels in the membrane permeate. It is expected that a loss of membrane integrity is the cause of this drop in performance.
The initial results show that the DOC level in the NF permeate is below the DOC level in the RGF permeate, after which it is consistently above. Yorkshire Water was very encouraged with the results achieved to date. Possible reasons for the loss of membrane integrity are fiber breakage or bad CIP protocol (e.g. the use of harmful surfactants).
Pilot Test (8”module) Norvatten (SE) – direct drinking water production
To investigate the possible application of the LbL coated HFS membranes at the water treatment work Görvälnverket of Norvatten an comprehensive pilot trial is performed. The performance tests are done with a fully automated containerized 8” UF-NF pilot (pilot 80), equipped with one 8” full-scale HFS module coated with 2 bilayers of PDADMAC/PSS (40 m2 membrane surface).The goal of the plant is to reduce the DOC and color from surface water for the production of drinking water. For this, it was stated that the UV254 adsorption of the permeate needs to be reduced by >80% compared to that the feed for a full scale process.
Major Results
After a period with increased filtration fluxes up to 20 lm-2h-1, the membrane resistance is stable and fluctuates only in a small range possibly due to measuring inaccuracies. Even if the recovery is increased from 50 to 90%, the membrane resistance is constant in time. The membrane retentions for UV254¬ varies between 87.6 – 91.6%, for Pt-Co between 87.5 – 97.5% and for TOC between 82 – 89% during the pilot trial. The results at the Norvatten plant show that the LbL coated HFS membrane perform very well in a large scale process. The demands by the customer (>80% UV254-abs retention) can be obtained with the membranes.
Achievements during M19-M36
Pilot tests of RWB coated LbL membranes for direct water treatment. Concept looks promising, but still the costs are too high due to relative low performance (i.e. in-field permeability) compared to standard RWB membranes and/or alternative treatment methods.
Full scale pilot test at Yorkshire for X-Flow coated LbL membranes. Yorkshire Water was very encouraged with the results achieved to date. This observed sudden change in the selectivity of the membrane seems to be related with the integrity of the module in that period.
Full scale pilot test at Norvatten for X-Flow coated LbL membranes. the LbL coated HFS membrane perform very well in a large scale process. The demands by the customer (>80% UV254-absorption retention) can be obtained with the membranes.
Industrial waste water treatment and reuse
Side stream digestate treatment for (enhanced) bio-energy production, nutrient recovery and water reuse. (RWB)
Multiple pilot test trails were executed using digestate as pilot feed water. All trails executed were completed within the stated time frame (M25 – M36) without delays or major setbacks.
Application : side stream digestate treatment;
Feed water : digestate, Borgercompagnie, Groningen, The Netherlands (NL);
Module 1 : ceramic based LbL membrane module, active NF top layer (0,04 m2);
Module 2 : ceramic MF with enhanced surface area roughness by LbL/CNT (0,04 m2)
Concept 1 : (enhanced-) bio- energy production, nutrient recovery, water reuse
Concept 2 : productivity increase per m2 membrane area, drop in MF system costs.
Conditions : temperature (18 – 22 °C), backwash (P = 5 bar), air flush (2 bar)
Outcome 1 : limiting- in-field permeability and (non-nutrient) compound retention;
Outcome 2 : no significant increase in the in-field permeability by the applied roughness.
Major Results
The obtained point of trade-off between productivity (i.e. in-field permeability) and non-nutrient compound retention was far from desired, resulting likely in too high system costs if compared to the combination of ceramic MF and spiral wound NF/RO. Roughening of the ceramic MF membrane surface area by LbL/CNT did not results in a significant higher in-field permeability and hence in a significant drop in the total ceramic MF system costs. The outcome of the concept is therefore judged negatively.
Thickening of COD amount for energy recovery – combination of LbL and digester. (RWB)
This was not executed. The pilot tests trails on digestate (6.3.1) were extended instead.
Anaerobic waste water treatment at a brewery with LbL membranes. (X-Flow)
In this research, supported tubular membranes with 5,2 mm inner diameter have been coated by LbL technology and tested in a AnMBR pilot plant, which operates at a brewery. The test was set out to compare the retention of LbL coated membranes under similar process conditions as the UF membrane operates. The filtration fluxes achieved in this AnMBR are in the range of 15 to 18 l/m2h.
Major Results
The results show striking differences between sludge, UF permeate and NF permeate. The turbidity of the sludge is caused by high concentration of bacterial cells, whilst yellow coloration of the UF permeate is most likely caused by humus substances. NF permeate does not display any coloration when examined by eye. The retention on colour (Pt-Co) is 99% and on UV254nm absorption is 69% for a negatively charged LbL tubular membrane.
The results show, that it is possible to filtrate directly AnMBR sludge from a brewery with LbL coated tubular nanofiltration membranes. The produced water is in one single step ready to be reused in the industrial process (e.g. cooling water, cleaning water, etc.).
Tests on metal recovery on artificial effluent (H2SO4, cupper, iron, etc.) Separation of acid from metal. (LUT)
LUT performed filtrations with a copper(II) sulfate/sulfuric acid feed solution based on typical mining effluents produced by customers of Outotec. LUT also performed CuSO4/H2SO4 filtrations trials with a (PDADMAC/PSS)3 coated tubular SiC membrane.
Major Results
Results show some separation between metal and acid (metal is somewhat rejected as well as acid but slightly lower extent than metal). PDADMAC-terminated PEM membrane seems to perform slightly better at least in terms of flux. Although these results do not show superior now, the test conditions are very critical for metal/acid separation and here it was done only at one point (one flux value).
Despite the high pure water permeability and high Mg2+ rejection of the (PDADMAC/PSS)3 coated CNT+SiC membrane, Cu2+ rejections remained relatively low in the CuSO4/H2SO4 filtration experiments.
Heavy metal and metalloids removal from industrial wastewater generated by wood and metal industry. (LIQ)
Laboratory pilot tests – waste water metal and wood industry
The objective of this experimental study was to investigate the performance of various LbL-coated tubular SiC membranes from LIQ during filtration of two different industrial wastewaters. The first water originated from a metal production process, in which ore and electronic waste are smelt and subsequently quenched with seawater. The second wastewater contains the same kind of hazardous compounds, but it is surface water from an industrial site in Denmark, where wooden boards are pressure impregnated.
Major Results
Feed and permeate samples were withdrawn from the pilot unit during the filtration of the two wastewaters with each of the five membranes included in this work. From the analytical results it could subsequently be determined how much of the individual hazardous components were removed by the various membranes. The retention of the individual heavy metals was in the range of 60-100% for all LbL coated membranes and thereby markedly higher than retention of the non-coated membrane. The test showed furthermore that the coating layers were chemically and physically not affected by the wastewater allowing filtration at constant capacity and contaminant removal during several hours.
Field tests
On-site filtration tests were carried out at two different locations in order to investigate the performance of LbL coated SiC membranes during several days of continuous filtration. The first site was a ground water well in the outer peripheries of Copenhagen, the second site was a metal production facility.
The removal rate for the metal ions is still under investigation and can be found in detail in D6.1.
Achievements during M19-M36
A RWB LbL coated membrane was tested for direct digestate filtration to retain all non-nutrients in a single stage treatment, making recovery of valuable nutrients in a subsequent (recovery-) stage more easier. Due to the low in-field permeability combined with the water properties obtained, the cost impact was not beneficial.
A tubular LbL coated XFLOW membrane was developed to treat digestate directly. The water had a superior quality and can be reused in the process.
A LIQ LbL membrane was created to remove metals and metalloids from industrial waste water. The retention for the metals was remarkably higher than for the standard LIQ membrane.
WP 7 Nanosafety and Life Cycle Assessment (M7-M36)
Task Leader: CIC; Contributors: RWB, EKO
WP 7 aims at identifying the most critical processes in the LbL techniques applied in the project in order to advise on risk minimisation routes. The assessment of the environmental impact of the developed technologies throughout their life cycle whereas taking into account nanosafety issues has been carried out.
Task 7.1 Nanosafety assessment (M7-M24)
Task Leader: CIC; Contributor: EKO
The nanosafety assessment implemented within LbLBRANE was planned with the objective of evaluating the possible toxicological impact of the nanomaterials to be integrated in the membrane: multiwalled CNTs (MWCNTs). MWCNTs have been employed to fabricate a reinforcement layer between the support and the polyelectrolyte membrane. This reinforcement layer was fabricated on the basis of self assembly of CNTs modified with polyelectrolytes and surfactants.
Sub-Task 7.1.1 Release of nanomaterials (CIC)
The stability of the CNTs assembly was also studied as the liberation of CNTs must be avoided.
CNTs multilayers were fabricated in the quartz microbalance and exposed to acid and basic solutions for different times, up to 12 hours. No variance in the mass of the assembly could be observed, hinting that the assembly is stable.
Sub-Task 7.1.2 Ecotoxicity tests (CIC)
Cell proliferation and genotoxicity of modified CNTs have been measured using the MTT and comet assay respectively. Nor oxidized MWCNTs neither amine functionalized CNTs produced measurable DNA fragmentation measured as percentage and longitude of comet tail after electrophoresis of single cells. Poly sulfo propyl methacrylate (PSPM)-functionalized CNT provoked DNA fragmentation.
The MTT assay showed that oxidized CNTs have a moderate reduction in cell proliferation over 4 days using the Hep2G cell line while PSPM coated CNTs induce a decrease in proliferation up to a 5 % for the 3rd day. It was concluded that toxicity was related to the surface functionalization of the CNTs.
The toxicity of the assemblies of CNTs, formed by layers of CNTs coated with PAH and CNTs coated with PAH/PSS was measured with the MTT assay using the cell line A549. Cells were spread on the CNTs multilayer for these experiments. After 72 hs cell proliferation remained over 80 % indicating the assembly can be considered “non toxic”.
An analysis of the release scenarios throughout the life cycle of nanotechnology enabled water treatment membranes –be it incorporating CNTs or with a nanostructured surface of polyelectrolyte multilayer- has been developed together with an analysis of the different tests that can be applied for their ecotoxicological evaluation in drinking water applications.
It was concluded that: 1) Complete and operational modules are needed to be tested in “real life” conditions for nano-release assessment: operation, maintenance. The only standard that could be applicable given the status of implementation of LbLBRANE is that of the UK – In particular the BS 6920. This test protocol describes a simple approach to generate leachates and assess their cytotoxic response. No mutagenicity is assessed, for instance. 2) The assembled CNT multilayers as such do not show a measurable toxicity. 3) Finally, to date, neither PDACMAC nor CNTs are on the positive lists of chemicals in contact with drinking water. A formal request has been submitted by X-FLOW for the inclusion of PDACMAC.
Task 7.2 Life Cycle Assessment (M7-M36)
Task Leader: EKO; Contributor: CIC
The objective of this task was assessing positive and negative effects towards the environment during the different life cycle stages of nanotechnology based membranes compared to conventional solutions. A quantitative basis for the selection of the most environmentally friendly alternative is provided.
To this aim, three comparative studies have been performed according to the standardised methodology of Life Cycle Assessment (LCA) (ISO 14040:2006; ISO 14044:2006). SimaPro 7 Modeling Software and Ecoinvent Database have been used as primary tools.
This task has been carried out by EKO with the support of CIC. Industrial partners with relevant background on membranes manufacturing (XFLOW and LIQTECH) and/or water treatment plants design and operation (RWB) have actively contributed to present task by the definition of case studies, compilation of inventory data for LCA, iterative review of the results obtained in the modeling phase and interpretation and improvement of the results obtained (focusing on issues related to the scaling-up of developed technologies). Academic partner RWTH has provided some inputs for the inventory data on LIQTECH’s membrane, in relation to the quantity of polyelectrolytes used for membrane coating.
As a general consideration, the application of the LbL technology has considered the use of PSS and PDADMAC.
Case Study 1 – Drinking water production, polymeric membranes - XFLOW
The functional unit of this study was defined as the production of 1 m3 of potable water. A comparative approach of two water treatment processes for drinking water production has been carried out. The reference system includes two stages: UF pretreatment followed by NF and this is compared to a nanofiltration process integrating the technology developed within the LbLBRANE Project based LbL technology. It has been assumed that the outcomes for drinking water production of the LbL technology on the basis of UF polymeric membranes without a pretreatment step can be assimilated to those of the spiral wound thin film composite membranes (NF 270 – FILMTECTM) after the necessary UF pretreatment process. Inventory data have been obtained from X-FLOW, literature sources or recalculated from the primary data provided by RWB.
The most relevant outcomes of present case study are summarized next: 1) The use of water treatment membranes manufactured using the LbL deposition of polyelectrolytes on traditionally manufactured UF polymeric membranes offers significant advantages from the environmental perspective, reducing all impact indicators –except the Terrestrial ecotoxicity-. This reduction is attributed to the avoidance of the pre-treatment UF stage, which has been traditionally necessary to condition the water for the NF process. 2) The highest environmental impacts are the climate change and fossil depletion. These impacts are closely related to the energy consumption of both systems. The UF operation is responsible for the 31% of the impacts approximately, while the 67% of the impacts are related to NF operation process. In the case of the LbL system, the tendency observed is the same, being the operational stage the major contributor to most indicators (87% of the impacts on average). The impact of these operational stages is mainly related to the energy consumption required. In fact, the minimization of energy consumption in water treatment processes represents a major environmental challenge.
Case study 2 - Drinking water production, ceramic membranes – RWB
The functional unit of this study was defined as the production of 1 m3 of potable water at the quality stipulated. A comparative approach of two water treatment processes for drinking water production was carried out. The reference system includes two stages: coagulation followed by MF ceramic pretreatment (in detail, the microfiltration process is divided into 3 different sub-processes: MF, coagulation and buffer between MF and NF) and then spiral wound polymer NF and this compared to a nanofiltration process integrating the technology developed within LbLBRANE on MF ceramic membranes that avoids the need of a pretreatment process. It has thus been assumed that the outcomes for drinking water production of the LbL technology on the basis of MF ceramic membranes without a pretreatment step can be assimilated to those of the spiral wound thin film composite membranes (NF 270 – FILMTECTM) after the necessary pretreatment processes detailed earlier.
The most relevant outcomes of present case study are summarized next: 1) The use of water treatment membranes manufactured using the LbL deposition of polyelectrolytes on traditionally manufactured MF ceramic membranes does not offer a significant enhancement from the environmental perspective despite the fact that the pretreatment stage has been assumed as unnecessary for the LbL system. In fact, the value of most of the environmental indicators is higher compared to the values of the reference system. 2) The highest environmental impacts are the climate change and fossil depletion. These impacts are closely related to the energy consumption of both systems. 3) If the impacts are analyzed per process in the reference system both operation stages and coagulation process contribute mostly to the selected indicators, being the MF and NF membrane manufacturing and installation construction processes negligible in terms of environmental impact. It is worth highlighting that the MF operation is responsible for the 13% of the impact approximately, and the coagulation for the 24%, while the 54% of the impact is related to NF operation process. In the case of the LbL system, the tendency observed is the same, being the operational stage the major contributor to most indicators (94% of the impacts on average). The impact of these operational stages is mainly related to the energy consumption required. The negative outcome of present assessment is related to the limiting flux in the case of the LbLBRANE Membrane. Furthermore, it should be noticed that the treatment process for sludge generated due to coagulation was not included in the reference system and therefore the environmental impacts associated to this process have not been accounted for.
Case study 3 – Metal recovery, Silicon Carbide membranes - LIQTECH
The functional unit of this study was defined as the treatment of 1 m3 of industrial wastewater at the quality stipulated. A comparative approach of two ultrafiltration processes of industrial wastewater is conducted: the reference system includes the UF silicon carbide membrane manufacturing as well as the installation construction and operation, while the LbL system includes the silicon carbide membrane manufacturing, the LbL coating of the UF membrane, installation construction and operation.
The most relevant outcomes of present case study are summarized next: 1) Unlike the previous case studies, XFLOW and RWB, in the case of LIQTECH the differences between the reference system and the LbL system are negligible. The inventories of both systems are the same, except for polyelectrolytes consumed in the LbL coating. Consequently, the environmental performance of both systems is almost identical. 2) The LbL system is expected to generate a tighter membrane which increases the retention of dissolved substances in wastewater, increasing the quality of the treated water in comparison with LIQTECH’s actual membranes. 3) When analyzing the unit processes, as in the previous case studies, operation stage is the one that produces the highest environmental impacts, due to the energy consumption required.
Task 7.3 Life Cycle Costing (M22-M36)
Task Leader: RWB
A life cycle costing study (LCC) in close combination with a LCA study is an excellent first- tool to determine the feasibility of a possible (industrial-) end product. Especially for an end product business case of which the exact- outcome is very difficult to determine in an early stage of the product development trajectory, an LCC could have an additional value to determine the possible and/or necessary development- and exploitation routes.
Polymer based LbL membrane modules, developed by (lead-) beneficiary B.08 – XFLOW have already been launched, indicating the (commercial-) feasibility of this end product. For ceramic based LbL membrane modules (i.e. lead- beneficiaries B.04 – RWB and B.10 – LIQ), the end product feasibility is not yet that clear.
The major drawback for usage as a LbL support is the (higher-) investment costs (raw materials, membrane production) compared to a polymer support. It was therefore mutually agreed upon to execute a (comprehensive-) LCC study on ceramic based LbL modules.
The applied approach for the determination of the total system costs of the “LbL” system (i.e. LbL membrane modules, ceramic based) included the following costs: Equipment, piping, instrumentation, Control system, control panels, PLC’s, etc.; Project labour fees; Consumable costs; Chemical costs; Energy costs.
The total system costs over a system lifetime of 15 years are a factor 2,24 higher for the “LbL” system compared to the “conventional” system (i.e. pre-treatment: coagulation + ceramic MF, followed by spiral wound polymer NF. The results clearly indicate that the ceramic based LbL membrane module needs to be further developed and/or upgraded to a “second generation” module (i.e. product) in order to overcome the determined higher system total costs factor of 2,24 and hence to end-up with an commercial competitive product for the defined study case.
Module development should be focused on reducing the LbL layer resistance for water permeation and drainage/collection by target engineering of the NF (i.e. “LbL”) top layer, resulting in an enhanced in-field productivity per square meter membrane surface area at a similar or slightly increased trans membrane differential pressure operation.
Potential Impact:
Potential impact
The Layer-by-Layer (LbL) production technique, to prepare low pressure nanofiltration (NF) membranes from water soluble polyelectrolyte (PE) solutions, compared to the conventional thin film composite (TFC) technique is of major importance due to the REACH regulation. Using organic solvents such as hexane in the TFC production is a major problem due to the REACH regulation, therefore it is necessary to provide a method, which is environmentally friendly (water based) and has thus a high socio-economic effect on the society due to the LbLBRANE project.
Removing endocrine substances (EDC) from surface water with LbL membranes compared to conventional filtration systems is of further interest. The contributions of this project to the scientific, social and economic improvements of the EU are of major importance. Endocrine substances in our drinking water, which pollute our resources have to be removed to maintain a high quality drinking water stream. The membrane system, developed in the LbLBRANE project has major economical (no solvents, easy applicable, stable for harsh cleaning conditions, low cost, regenerable under mild and environmentally conditions, high performance and extended lifespan) and therefore social advantages compared to conventional treatment systems.
The main difference between the LbL system and the conventional NF or reverse osmosis (RO) system is the ability of the LbL system to use a membrane with comparable retentions than mentioned before, but to use a membrane, which impact on the environment, due to its production method and the tailor made purpose, is beneficiary to the conventional systems. These statements are also supported by the life cycle assessment (LCA) performed during the project. Furthermore, conventional system, even RO systems have big problems with the separation of the endocrine compounds because a lot of them are very hydrophilic, which means the endocrines get recognized by the membrane likely as water. Conventional systems separate on solution-diffusion mechanism and let water pass through the membrane because of its high affinity to water. When the endocrine materials are now recognized comparable to water, they can easily pass the membrane together with the water; therefore the removal rate of endocrine substances is limited. Introducing charge, with the LbL system, kept the retention constant, while improving the flux through the membrane. This reduces the amount of modules needed and is beneficiary for the industry by reducing operational and capital expenses.
The new water framework and the RIVM Report 703719064/2010 strongly define the awareness of emerging contaminants in European surface water and show the need for new techniques to remove micro-pollutants. The water framework shows that safe drinking water is the backbone of social and economic live in the world.
If this legislation would be defined European wide, the market potential for this kind of new developments would be large, because of the involvement of Municipal and private authorities. But, this legislation is not clear at the moment, and this is the biggest risk for a membrane producer at the present time. It is not known yet, if and when this legislation will be introduced. Up to then, no one will introduce this new and mainly more expensive technique to remove these contaminants from drinking water sources.
For the participation in an FP7 project like this it is important that large companies, as Pentair X-Flow, to deal with these uncertainties. First of all it is important to build up a strategy on broad product diversity. It is important to sell products not only in the same market (water-beverage), to have a broad spectrum of products (micro-, ultra- and nanofiltration) and to produce products from environmentally friendly sources (e.g. PE’s in water). The last point strongly fits into Pentair X-Flows strategy and therefore participating in LbLBRANE was a low risk for the company. Therefore risk analysis of these projects, in which fundamentally new products are developed, is of major importance.
Concluding, the LbLBRANE project delivered a substantial contribution to the problems of safe and healthy drinking water in the European Union, but also worldwide. This technology development strengthens the pioneering role of the EU in a healthy mankind, the most important fact in human life.
Dissemination activities
LbLbRANE was very active within the Nano4Water cluster which was one of the main dissemination activities for the project. During the three years of the project we participated on every cluster meeting with several oral and poster contributions. Furthermore on the last meeting in January 2015 LbLBRANE organized a demonstrator to present our achievements. Therefore we hired a 2 times 4 m booth; brought 2 distinguish setups and demonstrated the simplicity and effectiveness of LbL technology on membranes. In addition we created 5 posters showing the structure of the project and the major results we could achieve during the project time.
Furthermore the coordinator, John Erik Wong, visited several conferences in the field of membrane technology and LbL technology to present LbLBRANE to a wide audience with different backgrounds. In total, the complete consortium contributed with 30 oral presentations and 20 poster presentations at different scientific workshops and conferences. Furthermore 7 peer reviewed articles are already published and several more are in preparation and will be published soon.
All dissemination activities regarding the LbLBRANE project have been regularly updated on the project website (www.lblbrane.eu) during its lifespan and will be maintained until 2022.
Exploitation of results
XFLOW commercialized already one product and will enter the market with different products in the future. The consortium and explicit XFLOW decided that patenting at this stage is not a good strategy to pursue. A patent violation from other competitors cannot be identified easily since the LbL film itself is just a few nanometre thick. Thus a visual investigation is more or less impossible. The amount of parameters needed to be controlled for an effective coating is rather high and hence a patent would reveal too much important information that the project hardly identified. With this information a competitor can develop a product quite fast. By varying one of the parameters slightly this product would even not violate any possible patent. Thus it was decided that a trade secret is for this type of foreground the better alternative.
In case of the ceramic membranes further developing and especially upscaling is needed for a successful commercialization. Although the permeability of ceramic LbL membranes is as good as the one of polymeric LbL membranes or classical nanofiltration membranes, it is for this type of membrane too low for a successful implementation on the market. The ceramic support itself is simply too expansive and thus the developed membranes are for standard application such as drinking water productions not competitive. However, niche markets with extraordinary requirements in stability, are from great interest for the developed membranes. In additions unique selling points such as the possibility of fully regeneration or the option to implement a coagulant free filtration process with these membranes will draw the interest in the future.
List of Websites:
www.lblbrane.eu
Contact details: John Erik Wong: john.wong@avt.rwth-aachen.de Daniel Menne: +49 241 80 29948 daniel.menne@avt.rwth-aachen.de
The shortage of drinking water in many regions on the planet, including parts of Europe, constitutes a real problem of increasing importance in a world with a growing population. In fact, the use of seawater, brackish water and wastewater for human consumption is becoming a viable alternative to pursue for the future. For this scope the development of novel, competitive and efficient membrane-based reclamation technologies is thus of paramount importance and requires the design and development of novel materials with improved performance and adjustable to the respective reuse applications.
Membrane processes have become a key component in water reclamation schemes due to the possibility to provide high quality water from membrane bioreactors or desalted water from nanofiltration (NF) or reverse osmosis (RO). In spite of the success of membrane technology, membrane separation systems suffer from a serious problem: membrane fouling. Membrane fouling due to plugging by solid particles or by large solutes is a quasi irreversible process and standard cleaning methods cannot recover the initial hydraulic permeability, unless operated at higher pressure. The downside of such measures is inevitably an increase in operation and maintenance costs as well as an adverse effect on the lifespan of the membrane, which is the reason why the whole concept of membrane processes should be revisited.
The general objective of LbLBRANE, scientific as well as industrial exploitation, is ultimately to strengthen the European membrane market by making nanotechnology available to large scale European membrane manufacturers and to provide nanotechnology-based solutions to end users. LbLBRANE is above all an ambitious AND realistic concept; promoting an innovative and promising cheap and green technology for the development of a novel membrane technology. Our focus is on membranes with superior combination of quality, performance, lifespan and competitive price compared to commercially available ones; our ultimate goal would be the production of a regenerable membrane. In order to successfully achieve all these goals, LbLBRANE has been structured in such a way that it covers a wide range of activities from the technology of membrane modification, through to structural module design, life cycle assessment, life cycle costing, nanosafety issues, pilot plant testing by end-users which has the capability to test, exploit, market and distribute the end product. A unique feature of LbLBRANE is having an expert team of world leading academic researchers from universities and research institutes working in close collaborations with leading industrial partners, SMEs and industries, ensuring competent input right from the membrane concept down to lab-scale production and optimisation before scaling-up in pilot plants for end users.
Project Context and Objectives:
The LbLBRANE project aims at applying a simple and powerful method, namely the “so-called” Layer-by-Layer (LbL) technology, to develop a versatile and generic procedure for the fast fabrication of low-cost, stable, chemical-resistant polyelectrolyte membranes. The focus is towards the realization of membranes which could be regenerated in-situ under mild and environmentally friendly conditions and with extremely high permselectivity and mechanical robustness. The ultimate aim is towards implementation of LbL on large-scale, from module design and construction to end-users, especially for water reuse and metal/acid recovery.
The concept is to use the LbL technology to modify the surface of membranes to create a thin active layer for high permselectivity. The LbL technology consists of the sequential deposition of polyelectrolytes on a surface in a precise and controlled manner. The challenge being whether the layers stay on the membrane after deposition and more importantly, are not washed away during filtration or (physical or chemical) standard cleaning procedures. LbLBRANE covers both polymeric as well as ceramic membranes, both very different in the material types, geometries but also pore sizes, ranging from microfiltration to nanofiltration. The use of nanomaterials have also been considered to enhance deposition and/or as a reinforcement of the mechanical properties of the membranes. With the use of the LbL lego-type approach, different architectures of layers are foreseen whereby one can envision a new type of membrane where the top fouled layers could be eroded by chemical treatment and more layers generated in-situ.
In order to achieve such ambitious goals, the consortium of LbLBRANE (visit us at http://www.lblbrane.eu) is composed of 6 universities with world-leading reputation on the LbL technology, 5 SMEs and one company that is Europe’s No. 1 polymeric membrane producer. The description of work (DOW) of LbLBRANE to fit the timing of the work plan is organized in various work packages (WP), led by a WP leader expert in the task assigned to that WP. Briefly, the scientific investigations are undertaken in “LbL technology for membrane modification” (WP1), “Microscopic characterization of membranes” (WP2), “Modelling of PEM membranes” (WP3), and “Macroscopic characterization of membranes” (WP4). “Upscaling: from membrane to module” (WP5) and “Pilot Work” (WP6) take care of the industrial requirements while working closely with “Nanosafety and Life Cycle Assessment” (WP7) to assess the environmental impact of the developed technologies. “Dissemination and exploitation” (WP8) and “Management” (WP9) ensures proper running of the project with emphasis on visibility and exploitation of results towards the design of a commercial concept.
LbLBRANE – a 3-year EU-funded project under the 7th Framework Programme (Grant agreement no. 281047) started in February 2012. In an early stage of the project the piloting could be started. The plants were already equipped with full size modules and the results were very promising. Further developments and stability test were performed and thus XFLOW entered the market with a product for drinking water production. It is a membrane that is able to remove colour and other organic substances but keeps the salt balance rather constant which is desired in drinking water production from surface water. Furthermore the project focused on denser membranes with the ability to retain bi-valent ions to 95 % and micro pollutants to a high degree. The results we achieved suggest that membranes based on LbL technique are competitive towards classical nanofiltration membranes. Hereby the LbL membrane has two major advantages towards the classical nanofiltration membrane. 1. During the production no organic solvents such as hexane, as it is used for the production of classical nanofiltration membranes, are required since the LbL film is prepared from aqueous solutions. 2. The LbL-based membrane is ready for effective cleaning strategies involving hypochlorite and backwashing, both not applicable on classical nanofiltration membranes. With these important advantages we are looking forward to more LbL-based membrane products from XFLOW.
For the ceramic membranes the work was focused on regenerable nanofiltration membranes. The pores of the applied ceramic support were much bigger as compared to the polymeric membranes making a LbL coating rather difficult. However, we were able to cover the pore and to produce a ceramic membrane with a LbL coating on top that retained bi-valent ions to 70 %. Also the regenerabilty was developed. By adding cationic surfactants and/or high concentrated salt solutions the LbL film can be removed before a new LbL film can be assembled making these membranes regenerable. The procedure can be repeated as often as desired without any performance loss. The main drawback of using a ceramic membrane as solely a support material for the LbL technology is the higher costs for the ceramic material if compared to a polymer support. Therefore, without a significant advantage in terms of pressure normalized productivity per square meter membrane area it will be difficult for this type of LbL membranes to commercially compete with classical polymer based nanofiltration membranes. Nevertheless, this type of LbL membranes are very stable and could, by making use of LbL (top-) layer regeneration, be implemented in applications or niche markets were harsh operating conditions occur.
Project Results:
WP 1 LbL Technology for membrane modification (M1-M30)
WP1 was dedicated to the use of the Layer-by-Layer (LbL) technique for the preparation of competitive, efficient and regenerable LbL-modified membranes for water treatment. The work was focused on the deposition of an active (Tasks 1.1 and 1.2) and regenerable (Task 1.4) separation layer made of polyelectrolyte multilayers (PEMs) and an intermediate reinforcing layer (Task 1.3) on model, membrane-like and membrane surfaces. In fact, it was possible to develop a sole LbL-separation layer combining the following properties: high retention of MgSO4 coupled with good flow, stability against standard cleaning and regenerability.
Task 1.1 Film formation and growth on membrane support (M1-M24)
Task Leader: CNRS; Contributors: CIC, ULEI
Brief summary of achievements during M1-M18
The membrane-like surfaces were initiated and developed
Homogeneous LbL deposition on model and membrane-like surfaces was achieved
LbL-film composition and deposition conditions were optimized to achieve the desired membrane properties
Optimum criteria for generating polyelectrolyte multilayers atop membranes were delivered in a general protocol
Achievements during M19-M24
As film growth and homogeneity were similar on model and membrane-like surfaces at the same preparation conditions, the effect of deposition and rinsing time on PEM properties (flux and selectivity) was studied by CNRS and XFLOW on LbL-modified hollow fiber (HF) membranes (XFLOW). Surprisingly, a major acceleration of the deposition and rinsing time by a factor five did allow maintaining the excellent properties of the polyelectrolyte separation layer. While the retention towards MgSO4 was similar for a deposition time of 3 min and 15 min, the flux measured was slightly higher for 3 min.
It was found that a minimum thickness of 17 nm for the separation layer PEI(PSS/PDADMAC)4PSS improved the retention towards MgSO4 from 5.9 ± 2.3 % (uncoated membrane) to 84.6 ± 1.9 % keeping the flux reasonable. Addition of extra layers only decreases slightly the flux without improving the retention of MgSO4. Deposition of the separation layer on a porous intermediate layer and not directly on the porous polymeric membrane avoids blocking membrane pores and allows reaching simultaneously high flux and high retention (Task 1.3).
SURF coated 490 different LbL films (M18-M36: 270) on XFLOW membranes and varied most possible parameters. The results on retention of MgSO4 and on permeability were measured by XFLOW. Most important parameter was the polyelectrolyte type. PAH/PSS yielded the best performance but due to instability against NaOCl the parameter screening in the second reporting period was concentrated to more stable PDADMAC/PSS coating. For PDADMAC/PSS coatings the permeability decreases until the 6th layer. For further layers the permeability is almost constant independent of outermost layer charge. Retention strongly increases after the 5th layer (threshold). There is a clear Odd-Even effect; when the outermost layer is positive, the retention becomes smaller. Higher pressure during coating in cross flow until 3 bar results in a significant increase in retention but a decrease in the permeability. Further minor effects were observed for polyelectrolyte concentration, coating time, coating temperature, annealing after coating and ion strength of washing solution.
Task 1.2 Comparison of the LbL deposition methods (M7-M18)
Task Leader: CNRS
Brief summary of achievements during M7-M18
Characterization of homogeneous PEM build-up on model and membrane-like surfaces using different deposition methods (dipping, spray-assisted and spin-assisted assembly)
Build-up of CNT-based films by dipping on model surfaces
Achievements during M19-M36
Even if spray-assisted and spin-assisted assembly cannot be used for functionalizing the internal surface of hollow fibres, more experiments were carried out by spray-assisted assembly to study the effect of the deposition and rinsing time and the number of layer pairs on the PEM properties. In addition, homogeneous carbon nanotubes (CNT)-based films were successfully prepared by spin-assisted assembly on model surfaces to investigate the effect of in-plane orientation of CNTs on mechanical properties of the reinforcing layer as a function of the preparation methods.
Task 1.3 Evaluation and optimization of the intermediate reinforcing layer (M7-M24)
Task Leader: CIC; Contributors: CNRS, ULEI
Brief summary of achievements during M7-M18
Preparation of stable suspensions of single and multiwalled CNTs
Optimization of the LbL-assembly of CNT-based films on model surfaces
Achievements during M19-M24 (or M36)
Following the results obtained on model and membrane-like surfaces, an intermediate reinforcing layer made of CNTs was built by static coating in hollow fibres (XFLOW) by CNRS and by dipping and solvent evaporation on flat ceramic membranes (LIQ) by CIC to investigate its impact on membrane properties (flux, retention and mechanical resistance) as a function of thickness, composition and architecture. For HF membranes, the addition of an intermediate layer composed of one layer of CNTs between the separation layer and the membrane surface increases already the flux by 30% without changing the retention value (around 85 %) compared to the system without an intermediate layer. Addition of extra CNT layers will increase the porous mesh structure of the intermediate layer and should still improve the flux (measurements by XFLOW in progress). In addition, the CNT reinforcement of PEMs leads to highly interesting mechanical properties (improvement of the Young’s modulus by a factor of 4).
Task 1.4 Film deconstruction and reconstruction for regenerable membranes (M13–M30)
Task Leader: ULEI; Contributors: CIC, CNRS, SURF
Brief summary of achievements during M13-M18
Protocols using surfactant, salt and pH were developed to remove PEMs partially or totally on model surfaces
PEM could be removed partially or totally and rebuilt several times
Achievements during M19-M30 (or M36)
Several subsequent deconstruction/reconstruction cycles for PDADMAC/PSS and PEI/PSS films were achieved on membranes-like surfaces by CNRS and in modules containing polymeric (XFLOW) and ceramic (LIQ and RWB) membranes by CNRS and SURF.
Prior to study the regenerabilty of PEMs in hollow fibre modules, the deconstruction protocol of PDADMAC/PSS films using 3 or 5 M of NaCl was first validated by CNRS on membrane-like surfaces. Then, regenerability of the PDADMAC/PSS film on the internal surface of hollow fibers was confirmed by measuring the flux and retention towards MgSO4 during deconstruction/ reconstruction cycles.
It was found that a residual film thickness corresponding probably to PEI/PSS complexes remains on hollow fibres after deconstruction. Thus, the measured flux after reconstruction of the PEM was slightly lower while the retention of MgSO4 was slightly higher.
In the meantime, SURF’s microscopic investigations showed that PEI/PSS coatings can be removed from LIQ SiC discs by treatment with NaOH solution at pH 12 at room temperature as evidenced by tracking of fluorescently-labeled PEI via confocal laser scanning microscopy. Although removal of PEI/PSS coatings with the relatively mild treatment of high pH is a promising method, the use of PEI/PSS coatings was discontinued in further stages of this project due to their instability against NaOCl, a cleaning chemical that is routinely used in membrane technology.
SURF further performed successful deconstruction/reconstruction of PDADMAC/PSS coatings on LIQ and RWB tubular ceramic membranes as presented in WP5 while CIC performed fouling experiments together with deconstruction/reconstruction cycles (also in WP5).
WP 2 Microscopic characterisation of membranes (M1-M30)
Task 2.1 Structural characterisation of PEM and nanomaterial (M1-M18)
Task Leader: CIC; Contributors: CNRS, ULEI
Brief summary of achievements during M1-M18
The topology of the supporting nanofiltration membrane, the PEM, as well as deconstruction and regeneration of the PEM were characterized by AFM.
The 3-d pore structure of nanofiltration membranes was imaged by means of SEM.
Ion Beam Microscopy (IBM) was used to characterize the elemental concentrations and distributions of N, O, S, Na in flat sheet membranes and hollow fibres.
Fluorescence confocal microscopy showed that depending on the molecular weight polyelectrolytes may penetrate into pores.
Achievements during M19-M30
No further work for task 2.1 was conducted.
Task 2.2 Characterising the composition and the interaction between the membrane components and between membrane components and ions (M4-M18)
Task Leader: ULEI; Contributor: CIC
Brief summary of achievements during M4-M18
FTR-IR investigations showed that the average hydrogen bond strength within polyethersulfone flat sheet membrane membranes is less than in free water. This was attributed to the interference of water binding to sulfonate and sulfone groups with cluster formation in bulk water. This finding may explain for the high water permeability through the narrow pores be reduced friction.
Ether, sulfone and sulfonate groups of PES membranes were identified as binding sites for divalent cations. Upon binding, water molecules are released from these sites and the order of the water network inside pores is further destabilized. The presence of the PEM enhances the binding of divalent cations to the active groups at the pore walls, thereby facilitating retention of divalent cations. Monovalent ions bind much less to characteristic groups of the pore walls.
Achievements during M19-M30
The sulfonate groups of the PEM represent binding sites for divalent cations, thereby significantly contributing to the retention of these ionic species.
IBM was used to quantify the retention of sodium and Ca within membranes. While sodium release takes only seconds the release of calcium ions lasts several minutes. These results confirm the large difference in binding behaviour between monovalent and divalent ions.
From our findings follows that it is not only the interaction of ions with the membrane sites in the pores which causes a significant decrease of diffusional transport of ions compared with water, but also at the same time the interference of these sites with the water structure causing an overall decreased hydrogen bond strength near the pore walls. The latter effect facilitates diffusional or maybe even convectional transport of water in nanopores due to increased slipping and reduced cluster size.
Task 2.3 Diffusion studies in PEM using fluorescence confocal techniques (M7-M24)
Task Leader: CIC; Contributors: ULEI, SURF
Brief summary of achievements during M7-M18
A novel approach for measuring the diffusion of dithionite WITHIN PEM´s of a thickness of only few nanometers based on fluorescence quenching of NBD – labelled PAH by dithionite was established. The diffusion of dithionite as a divalent anion with potential binding capacity to primary amines within PEM´s can be regarded as a model system for diffusion of ions within PEM´s with strong ion – PEM interaction.
The quenching rate depends on quencher concentration, layer composition, nature of the top layer and on background electrolyte concentration, BUT in all cases quenching occurs in the timescale of 102 - 103 s. This is a rather slow reaction-diffusion process for a nanoscale system. The intrinsic reaction rate of dithionite with NBD is high; consequently diffusion is the time limiting step. The kinetics of quenching was inconsistent with a classical diffusion process. The slow ion diffusion due to the binding to charged groups in the PEM layer represents a significant add-on for the separation performance of PEM modified membranes over bare nanofiltration membranes.
Achievements during M19-M24 (or M36)
Diffusion of dithionite was measured in PEM`s containing PDA selected by the consortium as a function of pH and a wide range of dithionite concentrations. The dependence of diffusion on pH observes a trend towards increased diffusion at higher pH.
For data analysis theoretical models of anomalous diffusion with various degrees of approximation were developed and applied to data analysis. One of the simplest models which still allowed a complete analytical treatment was that of a time dependent diffusion coefficient corresponding to stretched exponential behaviour.
A large degree of anomaly and the extremely small diffusion coefficient, as well as the pronounced odd-even effect caused by the influence of the top layer on the internal layer structure and layer ion concentration.
A comparison of RWB ceramic, LIQ SiC and XFLOW HFS polymer membranes with confocal laser scanning microscopy using fluorescent reporter molecules showed that smaller pore size of XFLOW membranes restricts the diffusion of polyelectrolytes into the pores, making these membranes ideal for LbL coating. Pores of RWB and LIQ membranes are coated inside to some extent, making pores smaller and significantly decreasing the permeability. RWB pores can be covered on top with PEM after 4 double layers of PDA/PSS but LIQ pores are too large to be covered on top via PEM.
Task 2.4 Assessment of mechanical properties and stability of PEM at the nanoscale (M10-M30)
Task Leader: ULEI; Contributor: CIC
Brief summary of achievements during M10-M18
Measurements of single polyelectrolyte molecule desorption forces from HFS and HFC membranes revealed that the adhesion energy per monomer is of the order of kT. Given the cooperativity of adhesion such energy gain is sufficient to ensure stable PEM layer formation on membrane supports.
Achievements during M19-M30
Young moduli of free-standing PE films depending on composition and carbon NT reinforcement were of the order of a few GPa. Reinforced CNT-based films were stronger but more brittle than polymer-based films. The CNT reinforcement of PEMs leads to highly interesting mechanical properties (improvement of the Young’s modulus by a factor of 4). We also found that these mechanical properties are not affected by the presence of salt during the PEM build-up.
Under normal operating conditions LbL-Films deposited on membranes should be stable toward rupture and spontaneous desorption. Chemical stability during cleaning is a much more critical issue and effectively limits the choice of polyelectrolyte species applicable for industrial nanofiltration devices.
WP 3 Modelling of PEM membranes (M4-M30)
Task 3.1 - Development of random-walk model for the prediction of microscopic mobilities of water and ions with PEM (M4-M18)
Task Leader: ULEI
Brief summary of achievements during M1-M18
Random walk simulations of diffusion in PEM´s were performed in the framework of the Continuous Time Random Walk (CTRW) model with waiting time distributions, the first moment of which has an infinite value corresponding to anomalous diffusion. This reflects the expected strong binding of the diffusing species to specific sites of PEM´s. The fluorescence decay involves also the reaction rate of the quencher with the reporter, which is described as diffusion limited process.
The experimentally observed subdiffusion behaviour in multilayers was alternatively simulated applying a Monte Carlo approach by a superposition of normal diffusion processes with distributed diffusion coefficients.
Achievements during M19-M36
Starting from CTRW simulations with appropriate underlying waiting time distributions it was possible to obtain in a second step relatively complex but analytical solutions, which were the basis for subsequent comparison of the simulated behaviour against experimental results.
Normal diffusion cannot explain the fast initial decay followed by a continuous slowing down of the diffusion process. Dithionite diffusion can very well described with an anomalous behaviour. The physical basis for this slow diffusion is the strong binding of the diffusing ion to two groups of the PEM matrix. It was further observed that ion binding itself modifies the properties of the matrix. The developed models were the basis for the analysis of diffusion data presented in WP2.
Task 3.2 Predicting membrane performance and behavior based on permeability for single ions (UPC)
Brief summary of achievements during M1-M18
Solution-Diffusion-Electro-Migration-Film model was used to obtain general solutions for trans-membrane transfer of electrolyte mixtures containing ions of 2, 3 and 4 different charges.
These solutions were used for detailed parametric analysis of Nanofiltration, Pressure-Retarded Osmosis and Forward Osmosis in multi-ionic solutions.
Achievements during M19-M36
Parametric solution for nanofiltration of 3 ions of different charges and its uses for the exploration of trends in the metal/acid separations
By using the previously obtained transcendental relationship between the total concentration of ions and the total ionic strength in the permeate we derived this parametric analytical solution for the case of 3 ions of different charges
C_p≡C(u_p )=[(G(u_p )-a(u_p )+u_0)/(G(u_p )-a(u_p )+u_p )]^((G(u_p )-a(u_p ))/2G(u_p ) )∙[(G(u_p )+a(u_p )-u_0)/(G(u_p )+a(u_p )-u_p )]^((G(u_p )+a(u_p ))/2G(u_p ) ) (1)
J_v (u_p )=(1/C(u_p ) -1)∙(Z_1-Z_2 )(Z_2-Z_3 )(Z_1-Z_3 )/(Π∙B_(-1)+B_0∙u_p ) (2)
where
a(u_p )≡(Π∙(B_1-Σ∙B_0 )+(B_2-Σ∙B_1 )∙u_p)/2(Π∙B_(-1)+B_0∙u_p ) (3)
G(u_p )≡√(〖a(u_p )〗^2-Π∙(Π∙B_0+B_1∙u_p)/(Π∙B_(-1)+B_0∙u_p )) (4)
B_i≡(Z_1^i∙(Z_2-Z_3 ))/P_1 +(Z_2^i∙(Z_3-Z_1 ))/P_2 +(Z_3^i∙(Z_1-Z_2 ))/P_3 (5)
Π≡Z_1 Z_2 Z_3 (6)
Σ≡Z_1+Z_2 〖+Z〗_3 (7)
P_k is the membrane permeance to the k-th ion, Z_k is the charge of k-th ion, J_v is the trans-membrane volume flow.
Eqs(1,2) provide a parametric relationship between the trans-membrane volume flow and the total ion concentration in the permeate, C_p using the relative double total ionic strength in the permeate, u_p, as the parameter. This relationship has been used to explore trends in the metal/acid separation by PEML membranes. We calculated reciprocal ion passages across PEML membrane with the ion permeances mimicking those of tubular PEML membrane determined by the trace ion method and summarized in the Deliverable 4.4. In these calculations, we have also taken into account concentration polarization and the effect of osmotic counter-pressure on the trans-membrane volume flow. The latter is relevant because in practical metal/acid recovery processes the feed concentrations are usually moderate to high, and the osmotic phenomena are quite important. The calculations showed that PEML can be very efficient in the process with metal/acid selectivities far exceeding 100. They also demonstrated that the situation of prevailing acid is generally beneficial because high metal rejections are reached already at fractions of osmotic pressure.
Task 3.3 CFD modelling of kinetics of membrane cleaning/regeneration in modules (Task Leader: UPC; contributor: RWTH)
No activities during M1-M18
Achievements during M19-M36
In view of the evolution of R&D needs, it has been decided to concentrate on the following modelling issues, which were found to be more important for the optimization of preparation of PEML and their practical application:
- kinetics of deposition of first polyelectrolyte layers on porous supports in view of “over-bridging” of larger pore entrances;
- CFD modelling of external mass transfer in tubular membranes with “decorated” internal surface in developed turbulent flows.
Modelling of kinetics of deposition of first polyelectrolyte layers on porous supports
We simulated numerically the kinetics of deposition of polyelectrolyte macromolecules within the entrance regions of pores of a nano-porous support. Due to the electrostatic repulsion, at each coating stage, the deposition is limited by the formation of one monolayer. Multilayer deposition is possible by subsequent deposition of layers with alternating charges. Deposition process in thin pores is complicated because the diffusivity of particles changes due to hydrodynamic interactions with the pore walls and becomes anisotropic. This effect was accounted for in the modelling. The principal conclusions from this modelling effort are:
Retardation of diffusion due to the macromolecule-wall interaction results in an essentially slower deposition and a thinner deposited layers formation for the same deposition time.
The optimal time of deposition depends on the polyelectrolyte concentration and macromolecule size.
By an increase of time an essentially thicker layer can be formed by 2-layer deposition with larger macromolecules compared to 3-layer deposition with smaller macromolecules.
In quasi-steady regimes the polyelectrolyte deposition takes place at the channel entrance only.
WP 4 Macroscopic characterisation of membranes (M1-M30)
Task 4.1 Characterisation of in-situ LbL assembly (M1-M12)
Task Leader: RWTH; Contributors: CONV, XFLOW, SURF
Brief summary of achievements during M1-M18
Design and build-up of OSMO Inspector designated for LbL coatings (CONV). With this setup first coatings with in-situ measurement of the TMP could be realized (RWTH).
Further measurements with several combinations of different polyelectrolytes, varied layer number, ionic strength, and pH were performed (RWTH, XFLOW, LUT, SURF)
Observation of the “Odd-Even” Effect and explanation by pore/surface dominant regime
Proof of layer presence by elemental analysis (EDX) and optical visualization by SEM (XFLOW, ULEI, RWTH) and degree of penetration into pores by CLSM for all membrane types (SURF)
Achievements during M19-M36
RWTH further focused on in-situ measurement of TMP evolution during coating on both, ceramic and polymeric hollow-fibre membranes. Coatings at different flux and different coating time but with the same amount of polyelectrolyte mass retained at the membrane surface were investigated. While the TMP-rise is a function of coating flux and time, the resistance values coincide on a master curve for both polyelectrolytes. The apparent resistance during filtration scales with the mass of polyelectrolyte that is transported into the lumen of the hollow fibre but is independent of the coating flux or coating time. Also the feed pressure level can be neglected as a potential parameter for the layer build-up since the pressure evolution differs for the coatings at the different flux levels. Possible compressing effects during layer build-up due to the pressure gradient between feed and permeate can thus be excluded.
Task 4.2 Stability of PEM (M1-M18)
Task Leader: RWTH; Contributor: XFLOW, SURF
Brief summary of achievements during M1-M18
Layer stability towards backflushing and crossflow was proven(XFLOW, RWTH, LUT)
First stability test for acid, base and high salt concentration were conducted (XFLOW)
In situ stability test with OSMO Inspector were carried out (RWTH)
Crosslinking of polyelectrolyte improved the salt stability but decreased the overall retention (RWTH, SURF)
Achievements during M19-M36
In order to evaluate the chemical resistance the LbL modified membranes were exposed to acid, base, NaOCl, high salt concentrations and surfactants. The PDADMAC/PSS system is stable to acid (pH 2, XFLOW) and base (pH 11 tested on the polymeric membrane (XFLOW), pH 12.5 tested on the ceramic support (RWTH)). Also NaOCl, a cleaning agent very commonly used in membrane filtration, does not harm the LbL modified membranes. 100 000 ppmh of NaOCl treatment resulted in no degradation (XFLOW, RWTH). However only two of 10 tested polycations were resistant against NaOCl, namely PDADMAC and PVBTMA (SURF). Cationic surfactants, such as CeTAB, DoTAB, and TTAB, were found to be possible candidates to remove the layers (SURF, LUT). In addition the stability towards salt was evaluated (RWTH, LUT). A NaCl solution was filtered through the membrane at a constant flux while the TMP was logged and thus in-situ changes in the layer can be recognized by the layer resistance. At a NaCl concentration of 1 mol/l we observed first changes in resistance which indicate layer destruction. At higher salt concentrations above 3 mol/l, the degradation was much more pronounced. However, the instability towards cationic surfactants and high salt concentration can be used to regenerate the layer. A total regeneration of ceramic and SiC membranes in situ could be achieved by application of oxidizing piranha solutions without degradation of the inorganic membranes (SURF). This is further discussed in WP5. Since PDADMAC/PSS system has a limiting retention of about 90% P2B/PSS was investigated as an alternative polyelectrolyte system (LUT). Unfortunately the P2B/PSS system did not show a sufficient stability to NaOCl and thus was not further investigated.
The stability of the polyelectrolyte film against water filtration as a function of the pressure was performed on ceramic and polymeric membranes by means of CLSM (SURF). No change of the polymer amount and distribution could be found until a pressure difference of 3 bar.
Task 4.3 Evaluation of the membrane performance (M7-M24)
Task Leader: LUT; Contributors: RWTH, CONV, SURF
Brief summary of achievements during M7-M18
LbL modified membranes were evaluated by measuring the retention for MgSO4 and permeability. Properties of nanofiltration membranes with retention for bivalent ions and permeabilities of about 10 LMH/bar were observed (XFLOW, RWTH, LUT, SURF)
XFLOW applied a full scale module with LbL modified membranes for surface water and removed TOC and color for about 60 to 80 % and above 90 % respectively.
Achievements during M19-M36
Several different coating with different layer numbers, different coating fluxes or pressures, varied coating time, and varied salt concentration during coating were applied. All coated membranes were evaluated by measuring the pure water permeability and the retention for MgSO4 (bivalent ions). Some chosen candidates were characterized more in detail by determining the MWCO, and retention for different salts (monovalent, bivalent and mixtures, details can be found in Task 4.4). LUT conducted experiments by using three different polyelectrolyte system: a) PDADMAC/PSS, b) P2B/PSS, and c) PDAMAC/PAA. They found the best retention values for the PDADMAC/PSS system using MgSO4 and PEG. SURF and XFLOW further focussed on the PAH/PSS system with astonishing high retention of about 97 % for MgSO4 and above 90 % for NaCl. However, PAH is unfortunately not stable towards NaOCl. Nevertheless it is at present, by far, the highest retention of an LbL-modified membrane that we observed. This polyelectrolyte pair showed also the best retention for drugs and hormones (XFLOW, SURF). But further investigation on other polyelectrolyte system that yield high retention values with a good stability is necessary. RWTH further investigated the PDADMAC/PSS system. As already observed for the resistance during coating (Task 4.1) the properties of the resulting membranes depend only on the mass of polyelectrolyte retained in front of the membrane surface. That means that we can aim for target properties and obtain them through different fabrication conditions. Hence it proves, for the first time, how precisely the method allows to engineer desired pure water permeabilities and retention properties.
XFLOW conducted some work on protein adsorption and fouling. They measured the adsorption of BSA on PDADMAC and on zwitterionic polyelectrolytes such as PSBMA and PSBMA-AA. Both, the adsorption measured with ellipsometry on silicon wafers and the permeability decrease during BSA filtration, was less when using PSBMA or PSBMA-AA instead of PDADMAC as the terminating layer.
Task 4.4 Characterisation of ion rejection (M10-M27)
Task Leader: UPC; Contributors: CONV, SURF
Subtask 4.4.1 Adjusting experimental set-ups (UPC, CONV)
Brief summary of achievements during M1-M18
The set-up for the electrochemical concentration-step technique was modified to implement liquid delivery by a computer-steered syringe pump; the software was upgraded to make possible fully automatic data acquisition.
CFD simulations demonstrated that the originally planned configuration of a batch cell with a disk-like stirrer put on a hollow axis does not provide equally-accessible membrane surface.
CFD simulations revealed that in an alternative configuration of a rotating disk-like membrane the membrane surface is equally-accessible apart from a narrow membrane periphery that can be excluded from the filtration.
Based on this, a prototype of rotating-membrane test cell was designed, built and preliminary tested
Achievements during M19-M36
UPC developed one more test-cell design with equally accessible membrane surface, namely, developed turbulent cross-flow with discarded permeate from the entrance zone as described in D4.4.
In the concentration-step setup, a special mask was developed to limit the propagation of drop of non-equilibrium solution after the concentration step. This has considerably improved the signal reproducibility. Extensive measurements of transient membrane potential after concentration step performed for a lab-made polymeric support (provided by Pentair-X-Flow) coated with a variable number of bi-layers of PSS/PAH revealed an interesting feature of non-monotone dependence of signal on the number of bi-layers. Besides, they exhibited a relatively good reproducibility that improved with increasing number of bi-layers. We suppose this to be caused by the improving homogeneity of membrane surface properties with the progress in coating.
Subtask 4.4.2 Measurement of ion rejection (UPC)
Brief summary of achievements during M1-M18
First measurements of transient membrane potential after concentration step revealed clear correlations between the signal and the state of the surface (PEML coating).
Achievements during M19-M36
The turbulent cross-flow setup was employed to obtain experimental data by means of trace-ion method. These data were used for the calculation of ionic permeances reported in the database of D4.4. The rotating-disk setup suffered from leaks for some time but finally could be improved to provide reproducible data with commercial NF membranes (no leaks). In the case of PEML membranes, there still appear to occur some leaks supposedly related to a PEML damage by the membrane-sealing O-ring. Indeed, the rejection of Mg2+ was practically independent of trans-membrane volume flux and exceeds 97%. This made us believe that the Mg2+ rejection by the intact PEML was actually still much higher and the pressure-independent relative passage of ca.2.7% of Mg2+ was due to a leak caused by the PEML damage. Our measurements also revealed a considerable dependence of MgCl2 rejection on the type of support when using the same polyelectrolytes (and deposition procedure). With the tubular support the MgCl2 rejections did not surpass 80% whereas with the flat-sheet support it exceeded 97% and was probably still much higher (see above). The membrane hydraulic permeability was ca.2 times lower with the flat-sheet support. This may point to a denser PEML, which could also cause a higher rejection although the difference in the rejections is much more pronounced than in the permeabilitites.
WP 5 Upscaling: from membrane to module (M10-M30)
Task Leader: LUT; Contributors: RWTH, CIC, RWB, CONV, XFLOW, ULEI, SURF, LIQ
This WP aims to solve possible problems arising from scaling up from single membranes to full or semi-full scale modules:
designing of modules for in-situ LbL deposition
optimising protocol for best LbL deposition conditions inside modules
assessing performance of regenerable modules
This WP has been divided into three Tasks (Adapting module design and construction, Coating and regeneration process inside modules and Proof of concept – performance assessment) of which in Task 5.2 the most up-scaling work was planned to do (Sub-tasks Lab-scale module and Operational-scale module).
Task 5.1 Adapting module design and construction (M10-M18)
This Task is devoted to make changes needed and redesign existing modules and housings to enable LbL depositions inside modules. Different designs may be needed for lab-scale testing than for upscaled modules as well as the possibility to remove and reconstruct polyelectrolyte layers was to be taken into account.
Brief summary of achievements during M10-M18
Scaling work was actually started in WP4 by coating single fibres or very small (short) ceramic modules. Basic knowledge of coating on single fibre module (experience gained in WP4) was successfully transferred to modules containing several fibres and coating of several modules at the same time. Upscaling of polymeric modules was successfully done and full-scale commercial elements were LbL coated by XFLOW. Same work with ceramic modules turned out to be somewhat slower but coating protocol was created for them in semi-full scale modules. Coating itself could be performed in all sizes but LbL coated ceramic membrane performance was not satisfactory (even in small scale) due to their inherent macroscopic pores.
Achievements during M19-M36
Al2O3 ceramics (RWB)
Due to the too low in-field evaluated permeability (i.e. L/(m2*h*bar)), final design is a R&D scale- NF membrane module (0.04 m2, ceramic based) with an open feed structure. Two module types were designed, resulting in a broad application range tuned to the desired- operating and (chemical-) resistance conditions.
Type II was successfully used for lab-scale (in-situ-) regeneration experiments (see Task 5.2). Module design implemented allows for direct upscaling to a (small-) commercial scale: 0.4 m2.
SiC ceramic membranes (LUT, CIC, LIQ, SURF):
The module geometry and its active area were changed for the last coating experiments utilising CNT reinforcement layer prior to LbL layers. LIQ sent 40 nm pore diameter, 1 channel, L 250 mm, ID 6.0 mm membrane modules to CIC who coated them with a CNT layer using facilities of SURF. Then these CNT coated SiC monotubes were shipped to LUT who coated them with LbL layers and performed the usual tests using LIQ housing build for these monotubes. The SiC module was shifted to smaller monotubes due to limited amount of CNT solution. This way more modules could be tested with CNT reinforcing layer.
Task 5.2 Coating and regeneration process inside modules (M13-M24)
This task investigates different parameters to construct optimized LbL coating inside modules first in small scale and then in larger operational scale. Also regeneration of the coating after partial or full removal is studied. Adapted modules from previous task are utilized here. Utilization of CNT layers and other reinforcing substances prior to LbL layers to tighten and smooth out the rather open ceramic membranes was also looked at in this task.
Brief summary of achievements during M13-M18
A set of experiments have been done to look at the possibilities of regeneration. It was found that complete removal of LbL layers from polymeric membrane surface is not possible without destroying the substrate as well. Therefore the strategy with polymeric membranes was shifted and regeneration was not objective anymore (it was also independently found unnecessary too with polymeric membranes, see D5.1). Complete removal of LbL layers from pores of ceramic membranes was found hard as well. However, regeneration on top of incompletely removed LbL system resulted in even better performance than constructing LbL layers on clean pristine ceramic surface, see D5.2. It was found also that after the first regeneration, further LbL layers could be constructed rather reproducible manner.
Achievements during M19-M36)
Lab-scale (SURF, LUT, RWTH)
LIQ and RWB tubular membranes were tested for construction/deconstruction/ reconstruction inside modules (see D5.2)
LIQ tubular membranes were coated with 10 double layers of PDA/PSS. Complete deconstruction of these LbL coated layers is possible by subsequent treatment of membranes with DoTAB and NaCl. The order of application is crucial.
RWB tubular membranes were coated with 6 double layers of PDA/PSS. In contrast to LIQ membranes, DoTAB + NaCl treatment did not result in a complete layer removal
PDA/PSS layers on RWB membranes could be completely removed by a diluted pirahnha solution in module
Recoating of both RWB and LIQ membranes with PDA/PSS layers is possible
PDA/PSS coatings are stable against NaOCl and NaOH solutions
High Salt concentration can be used to destroy the film but the layer will never be removed completely.
LbL coated ceramic membranes with CNT reinforcing layer (LUT, CIC, LIQ, SURF, RWB, RWTH):
Due to relatively poor salt retention performance of only LbL coated ceramic membranes, it was tried to reinforce the substrate prior the LbL coating by carbon nanotube layer (CNT). CNT coating of SiC membranes was done by CIC on LIQ monotube membranes. LbL coating was done normally with a (PDADMAC/PSS)3 system by LUT and tested with dilute MgSO4 solution at neutral pH. Some of the results were very promising since Mg2+ retention increased from about 60% (without CNT layer) up to about 90% (with CNT middle layer) while permeability remained at the same level. However, the stability of the combined CNT+LbL layers was still rather weak since only one trial out of four was successful. RWTH applied CNTs prior to LbL coating on the RWB ceramic membrane. The flux decreased as with LbL coatings only (as a function of bilayers) but remained more than twice higher when a CNT layer was used even after 8 bilayers. This was due to bridging effect of CNT network produced over pore openings preventing PEs to enter deeply inside the pores during the LbL deposition process.
Operational-scale (RWB):
Type II membrane module outlined in Task 5.1 was implemented in the semi-bench scale pilot for continuous testing of the membrane module under high pressure backwash (BW, P = 5 bar) and air flush (i.e. AF, P = 2 bar) conditions.
No active NF top layer deterioration and/or removal were observed. In addition, no sealing-, integrity- or module problems were encountered. (In-situ-) regeneration was not yet executed on an operational scale.
Task 5.3 Proof of concept - performance assessment (M16-M30)
This task is for final testing and evaluation of best performant membranes in labtests and on-site as well and for longer periods of time if possible.
Brief summary of achievements during M16-M18
Due to some small delays in development of LbL membranes on ceramics, the tests with them were not actually started during M16-M18. However, the work with polymeric membranes carried out clearly faster and on-site tests with them were started before M16. The results are reported in WP 6.
Achievements during M19-M30 (or M36)
Within a short labscale pilot study the LbL membranes using different supports were benchmarked and compared with an commercial available nanofiltration spiral wound module (Tests and coating of all applied membranes was done by RWTH). As feed the effluent from a waste water treatment plant equipped with an ultrafiltration unit as the last step was employed. Detailed results are shown in D5.3.
Fouling was more pronounced on the LbL membranes than on the commercial DOW NF270 spiral wound module. This is not really surprising since the spiral wound module is an out-engineered product that has spacers to introduce turbulences that reduce fouling. However, after longer filtration time this membrane would also show a performance loss. And then the tubular LbL membranes would have the advantage of simple cleaning methods like backwashing and NaOCl treatment which are both not applicable on the DOW NF270 spiral wound module.
TOC removal was for all tested membranes comparable. The low TOC reduction of roughly 60 % showed that there are a lot of small organic compounds in the water that can pass all tested membranes.
The rejection for bi-valent anions was the best for the DOW NF270 but also the LbL membranes retained SO42- between 75 – 90 %.
The rejection for bi-valent cations was better for the LbL membranes than for the DOW NF270. The retention on the LbL membranes was even partly higher than the rejection for bi-valent anions which is really surprising and cannot be explained so far.
The small scale pilot study with real waste water showed that the LbL membrane has serious potential to be competitive to real NF products already on the market. Only the rejection of bi-valent anions was significantly higher on the DOW NF270 than on the LbL membranes.
We tested 4 differently coated XFLOW polymeric HFs membranes. One of these membranes had a coating that was done on low flux and only two bi-layers. As expected this membrane had a quite high permeability of roughly 30 LMH and a lower retention for the analysed compounds. It is not always desired to retain everything and therefore the LbL mechanism is optimally suited to prepare membranes that fit the needs of the intended separation process perfectly.
For the long term pilot tests where only the total organic contents of the feed needs to be reduced and electrolytes need to pass the membrane, the coatings presented that are less dense should be suitable. Therefore, for the direct filtration of surface water membranes with 2 and 3 bilayers will be tested in WP 6.
For the pilot test where a denser membrane is needed (e.g. for the removal of low molecular weight organics), the results presented here (by XFLOW) indicate that 2 bilayers will not be sufficient (however, recent results from RWTH show that, with the right coating conditions, quite dense layer could be obtained for even 1 bilayer). For these pilot studies we will therefore opt for denser coating on HFs membrane.
WP 6 Pilot Work (M25-M36)
Task Leader: XFLOW; Contributors: RWTH, RWB, LUT, LIQ
Municipal waste water treatment
Direct sludge filtration (tubular LbL NF) vs. effluent polishing with LbL systems for municipal applications – comparison of conventional UF vs. direct NF. (X-Flow)
Two different experimental set ups are performed for this task.
Direct sludge filtration with a tubular UF and a tubular LbL Membrane.
Effluent polishing of an aerobic membrane bioreactor (a-MBR) equipped with an Ultrafiltration (UF) membrane. UF permeate is treated again with an UF membrane and with three different LbL membranes.
Major Results
Tight LbL membranes remove 50% more organics than comparable UF membranes.
Effluent polishing with LbL coated membranes can remove up to 90% extra color and organics from the effluent.
A T2 membrane is an excellent candidate to remove organics without changing the salt balance dramatically.
LbL coating membranes is a perfect toolbox to produce tailor made membranes for the wishes and demands of the customer.
Comparison of a MF/NF270Dow vs. MF/NF LbL (MBR effluent polishing, focus on micropollutant tests) RWTH
This benchmark study was conducted by filtering effluent from a waste water treatment plant (Kaarst) with different membrane modules for one week. The waste water treatment plant is equipped with ultrafiltration membranes as the last step before the water is pumped to a river.
Major Results
Commercially available NF (DOW NF270) membrane performs better in terms of micro pollutant retention. In this research we focused on a polyelectrolyte system (PDADMAC/PSS) that is chlorine resistant (WP2, 4 and 5), a unique feature that the current NF membranes on the market does not have. Therefore the LbL membranes can be easily cleaned to ensure long term stability, knowing that the achieved membranes are not as dense as other LbL systems.
Achievements during M19-M36
Direct sludge filtration with LbL-coated membranes is possible and color retention is superior.
Effluent polishing with LbL-coated membranes can achieve directly dischargeable water.
The retention of the LbL system PDADMAC/PSS on micropollutants is inferior compared to commercial nanofiltration membranes.
Drinking water production
Drinking water production (non-chemicals, direct discharge, no pre-treatment). [RWB]
In total, two pilot test trails were executed with canal water (i.e. surface water). Both test trails were completed within the stated time frame (M25 – M36) without delays.
Application : drinking water production;
Feed water : canal water, Twentekanaal, Bornebroek, The Netherlands (NL);
Module : ceramic based LbL membrane module, active NF top layer (0,04 m2);
Concept : main concept features can be summarised as:
(1) direct intake without addition of chemicals to the feed water, (2) open feed module structure for suspended solid (SS) as well as partial ion removal (3) total treatment step reduction;
Outcome : obtained in-field permeability is limiting, resulting in too high system costs.
Major results
Although the concept looks promising in terms of treatment step reduction-, chemical reduction- and obtained water properties (i.e. permeate-), the final outcome of the concept proposed is judged negative. This negative outcome is primarily determined by the obtained membrane performance (i.e. evaluated in-field permeability), resulting in too high costs for the total treatment system.
Drinking water production (X-Flow)
Pilot Test (8”module) Yorkshire Water (UK) – direct THM precursor removal
An 8” inch (full scale) module coated was coated with 2 bilayers of PDADMAC/PSS and tested in a full scale pilot installation.The pilot plant operates semi-automatically, with a system to control the feed flow and pressure.
Major Results
In the initial stages of the experiments, the LbL membrane outperformed the current rapid gravity filters (RGF) on the removal of THM precursors (THM-Formation Potential). However, after roughly two months of operation, a change is observed. The significant increase in THM-FP levels in the membrane permeate, were also accompanied by an increase in the DOC levels in the membrane permeate. It is expected that a loss of membrane integrity is the cause of this drop in performance.
The initial results show that the DOC level in the NF permeate is below the DOC level in the RGF permeate, after which it is consistently above. Yorkshire Water was very encouraged with the results achieved to date. Possible reasons for the loss of membrane integrity are fiber breakage or bad CIP protocol (e.g. the use of harmful surfactants).
Pilot Test (8”module) Norvatten (SE) – direct drinking water production
To investigate the possible application of the LbL coated HFS membranes at the water treatment work Görvälnverket of Norvatten an comprehensive pilot trial is performed. The performance tests are done with a fully automated containerized 8” UF-NF pilot (pilot 80), equipped with one 8” full-scale HFS module coated with 2 bilayers of PDADMAC/PSS (40 m2 membrane surface).The goal of the plant is to reduce the DOC and color from surface water for the production of drinking water. For this, it was stated that the UV254 adsorption of the permeate needs to be reduced by >80% compared to that the feed for a full scale process.
Major Results
After a period with increased filtration fluxes up to 20 lm-2h-1, the membrane resistance is stable and fluctuates only in a small range possibly due to measuring inaccuracies. Even if the recovery is increased from 50 to 90%, the membrane resistance is constant in time. The membrane retentions for UV254¬ varies between 87.6 – 91.6%, for Pt-Co between 87.5 – 97.5% and for TOC between 82 – 89% during the pilot trial. The results at the Norvatten plant show that the LbL coated HFS membrane perform very well in a large scale process. The demands by the customer (>80% UV254-abs retention) can be obtained with the membranes.
Achievements during M19-M36
Pilot tests of RWB coated LbL membranes for direct water treatment. Concept looks promising, but still the costs are too high due to relative low performance (i.e. in-field permeability) compared to standard RWB membranes and/or alternative treatment methods.
Full scale pilot test at Yorkshire for X-Flow coated LbL membranes. Yorkshire Water was very encouraged with the results achieved to date. This observed sudden change in the selectivity of the membrane seems to be related with the integrity of the module in that period.
Full scale pilot test at Norvatten for X-Flow coated LbL membranes. the LbL coated HFS membrane perform very well in a large scale process. The demands by the customer (>80% UV254-absorption retention) can be obtained with the membranes.
Industrial waste water treatment and reuse
Side stream digestate treatment for (enhanced) bio-energy production, nutrient recovery and water reuse. (RWB)
Multiple pilot test trails were executed using digestate as pilot feed water. All trails executed were completed within the stated time frame (M25 – M36) without delays or major setbacks.
Application : side stream digestate treatment;
Feed water : digestate, Borgercompagnie, Groningen, The Netherlands (NL);
Module 1 : ceramic based LbL membrane module, active NF top layer (0,04 m2);
Module 2 : ceramic MF with enhanced surface area roughness by LbL/CNT (0,04 m2)
Concept 1 : (enhanced-) bio- energy production, nutrient recovery, water reuse
Concept 2 : productivity increase per m2 membrane area, drop in MF system costs.
Conditions : temperature (18 – 22 °C), backwash (P = 5 bar), air flush (2 bar)
Outcome 1 : limiting- in-field permeability and (non-nutrient) compound retention;
Outcome 2 : no significant increase in the in-field permeability by the applied roughness.
Major Results
The obtained point of trade-off between productivity (i.e. in-field permeability) and non-nutrient compound retention was far from desired, resulting likely in too high system costs if compared to the combination of ceramic MF and spiral wound NF/RO. Roughening of the ceramic MF membrane surface area by LbL/CNT did not results in a significant higher in-field permeability and hence in a significant drop in the total ceramic MF system costs. The outcome of the concept is therefore judged negatively.
Thickening of COD amount for energy recovery – combination of LbL and digester. (RWB)
This was not executed. The pilot tests trails on digestate (6.3.1) were extended instead.
Anaerobic waste water treatment at a brewery with LbL membranes. (X-Flow)
In this research, supported tubular membranes with 5,2 mm inner diameter have been coated by LbL technology and tested in a AnMBR pilot plant, which operates at a brewery. The test was set out to compare the retention of LbL coated membranes under similar process conditions as the UF membrane operates. The filtration fluxes achieved in this AnMBR are in the range of 15 to 18 l/m2h.
Major Results
The results show striking differences between sludge, UF permeate and NF permeate. The turbidity of the sludge is caused by high concentration of bacterial cells, whilst yellow coloration of the UF permeate is most likely caused by humus substances. NF permeate does not display any coloration when examined by eye. The retention on colour (Pt-Co) is 99% and on UV254nm absorption is 69% for a negatively charged LbL tubular membrane.
The results show, that it is possible to filtrate directly AnMBR sludge from a brewery with LbL coated tubular nanofiltration membranes. The produced water is in one single step ready to be reused in the industrial process (e.g. cooling water, cleaning water, etc.).
Tests on metal recovery on artificial effluent (H2SO4, cupper, iron, etc.) Separation of acid from metal. (LUT)
LUT performed filtrations with a copper(II) sulfate/sulfuric acid feed solution based on typical mining effluents produced by customers of Outotec. LUT also performed CuSO4/H2SO4 filtrations trials with a (PDADMAC/PSS)3 coated tubular SiC membrane.
Major Results
Results show some separation between metal and acid (metal is somewhat rejected as well as acid but slightly lower extent than metal). PDADMAC-terminated PEM membrane seems to perform slightly better at least in terms of flux. Although these results do not show superior now, the test conditions are very critical for metal/acid separation and here it was done only at one point (one flux value).
Despite the high pure water permeability and high Mg2+ rejection of the (PDADMAC/PSS)3 coated CNT+SiC membrane, Cu2+ rejections remained relatively low in the CuSO4/H2SO4 filtration experiments.
Heavy metal and metalloids removal from industrial wastewater generated by wood and metal industry. (LIQ)
Laboratory pilot tests – waste water metal and wood industry
The objective of this experimental study was to investigate the performance of various LbL-coated tubular SiC membranes from LIQ during filtration of two different industrial wastewaters. The first water originated from a metal production process, in which ore and electronic waste are smelt and subsequently quenched with seawater. The second wastewater contains the same kind of hazardous compounds, but it is surface water from an industrial site in Denmark, where wooden boards are pressure impregnated.
Major Results
Feed and permeate samples were withdrawn from the pilot unit during the filtration of the two wastewaters with each of the five membranes included in this work. From the analytical results it could subsequently be determined how much of the individual hazardous components were removed by the various membranes. The retention of the individual heavy metals was in the range of 60-100% for all LbL coated membranes and thereby markedly higher than retention of the non-coated membrane. The test showed furthermore that the coating layers were chemically and physically not affected by the wastewater allowing filtration at constant capacity and contaminant removal during several hours.
Field tests
On-site filtration tests were carried out at two different locations in order to investigate the performance of LbL coated SiC membranes during several days of continuous filtration. The first site was a ground water well in the outer peripheries of Copenhagen, the second site was a metal production facility.
The removal rate for the metal ions is still under investigation and can be found in detail in D6.1.
Achievements during M19-M36
A RWB LbL coated membrane was tested for direct digestate filtration to retain all non-nutrients in a single stage treatment, making recovery of valuable nutrients in a subsequent (recovery-) stage more easier. Due to the low in-field permeability combined with the water properties obtained, the cost impact was not beneficial.
A tubular LbL coated XFLOW membrane was developed to treat digestate directly. The water had a superior quality and can be reused in the process.
A LIQ LbL membrane was created to remove metals and metalloids from industrial waste water. The retention for the metals was remarkably higher than for the standard LIQ membrane.
WP 7 Nanosafety and Life Cycle Assessment (M7-M36)
Task Leader: CIC; Contributors: RWB, EKO
WP 7 aims at identifying the most critical processes in the LbL techniques applied in the project in order to advise on risk minimisation routes. The assessment of the environmental impact of the developed technologies throughout their life cycle whereas taking into account nanosafety issues has been carried out.
Task 7.1 Nanosafety assessment (M7-M24)
Task Leader: CIC; Contributor: EKO
The nanosafety assessment implemented within LbLBRANE was planned with the objective of evaluating the possible toxicological impact of the nanomaterials to be integrated in the membrane: multiwalled CNTs (MWCNTs). MWCNTs have been employed to fabricate a reinforcement layer between the support and the polyelectrolyte membrane. This reinforcement layer was fabricated on the basis of self assembly of CNTs modified with polyelectrolytes and surfactants.
Sub-Task 7.1.1 Release of nanomaterials (CIC)
The stability of the CNTs assembly was also studied as the liberation of CNTs must be avoided.
CNTs multilayers were fabricated in the quartz microbalance and exposed to acid and basic solutions for different times, up to 12 hours. No variance in the mass of the assembly could be observed, hinting that the assembly is stable.
Sub-Task 7.1.2 Ecotoxicity tests (CIC)
Cell proliferation and genotoxicity of modified CNTs have been measured using the MTT and comet assay respectively. Nor oxidized MWCNTs neither amine functionalized CNTs produced measurable DNA fragmentation measured as percentage and longitude of comet tail after electrophoresis of single cells. Poly sulfo propyl methacrylate (PSPM)-functionalized CNT provoked DNA fragmentation.
The MTT assay showed that oxidized CNTs have a moderate reduction in cell proliferation over 4 days using the Hep2G cell line while PSPM coated CNTs induce a decrease in proliferation up to a 5 % for the 3rd day. It was concluded that toxicity was related to the surface functionalization of the CNTs.
The toxicity of the assemblies of CNTs, formed by layers of CNTs coated with PAH and CNTs coated with PAH/PSS was measured with the MTT assay using the cell line A549. Cells were spread on the CNTs multilayer for these experiments. After 72 hs cell proliferation remained over 80 % indicating the assembly can be considered “non toxic”.
An analysis of the release scenarios throughout the life cycle of nanotechnology enabled water treatment membranes –be it incorporating CNTs or with a nanostructured surface of polyelectrolyte multilayer- has been developed together with an analysis of the different tests that can be applied for their ecotoxicological evaluation in drinking water applications.
It was concluded that: 1) Complete and operational modules are needed to be tested in “real life” conditions for nano-release assessment: operation, maintenance. The only standard that could be applicable given the status of implementation of LbLBRANE is that of the UK – In particular the BS 6920. This test protocol describes a simple approach to generate leachates and assess their cytotoxic response. No mutagenicity is assessed, for instance. 2) The assembled CNT multilayers as such do not show a measurable toxicity. 3) Finally, to date, neither PDACMAC nor CNTs are on the positive lists of chemicals in contact with drinking water. A formal request has been submitted by X-FLOW for the inclusion of PDACMAC.
Task 7.2 Life Cycle Assessment (M7-M36)
Task Leader: EKO; Contributor: CIC
The objective of this task was assessing positive and negative effects towards the environment during the different life cycle stages of nanotechnology based membranes compared to conventional solutions. A quantitative basis for the selection of the most environmentally friendly alternative is provided.
To this aim, three comparative studies have been performed according to the standardised methodology of Life Cycle Assessment (LCA) (ISO 14040:2006; ISO 14044:2006). SimaPro 7 Modeling Software and Ecoinvent Database have been used as primary tools.
This task has been carried out by EKO with the support of CIC. Industrial partners with relevant background on membranes manufacturing (XFLOW and LIQTECH) and/or water treatment plants design and operation (RWB) have actively contributed to present task by the definition of case studies, compilation of inventory data for LCA, iterative review of the results obtained in the modeling phase and interpretation and improvement of the results obtained (focusing on issues related to the scaling-up of developed technologies). Academic partner RWTH has provided some inputs for the inventory data on LIQTECH’s membrane, in relation to the quantity of polyelectrolytes used for membrane coating.
As a general consideration, the application of the LbL technology has considered the use of PSS and PDADMAC.
Case Study 1 – Drinking water production, polymeric membranes - XFLOW
The functional unit of this study was defined as the production of 1 m3 of potable water. A comparative approach of two water treatment processes for drinking water production has been carried out. The reference system includes two stages: UF pretreatment followed by NF and this is compared to a nanofiltration process integrating the technology developed within the LbLBRANE Project based LbL technology. It has been assumed that the outcomes for drinking water production of the LbL technology on the basis of UF polymeric membranes without a pretreatment step can be assimilated to those of the spiral wound thin film composite membranes (NF 270 – FILMTECTM) after the necessary UF pretreatment process. Inventory data have been obtained from X-FLOW, literature sources or recalculated from the primary data provided by RWB.
The most relevant outcomes of present case study are summarized next: 1) The use of water treatment membranes manufactured using the LbL deposition of polyelectrolytes on traditionally manufactured UF polymeric membranes offers significant advantages from the environmental perspective, reducing all impact indicators –except the Terrestrial ecotoxicity-. This reduction is attributed to the avoidance of the pre-treatment UF stage, which has been traditionally necessary to condition the water for the NF process. 2) The highest environmental impacts are the climate change and fossil depletion. These impacts are closely related to the energy consumption of both systems. The UF operation is responsible for the 31% of the impacts approximately, while the 67% of the impacts are related to NF operation process. In the case of the LbL system, the tendency observed is the same, being the operational stage the major contributor to most indicators (87% of the impacts on average). The impact of these operational stages is mainly related to the energy consumption required. In fact, the minimization of energy consumption in water treatment processes represents a major environmental challenge.
Case study 2 - Drinking water production, ceramic membranes – RWB
The functional unit of this study was defined as the production of 1 m3 of potable water at the quality stipulated. A comparative approach of two water treatment processes for drinking water production was carried out. The reference system includes two stages: coagulation followed by MF ceramic pretreatment (in detail, the microfiltration process is divided into 3 different sub-processes: MF, coagulation and buffer between MF and NF) and then spiral wound polymer NF and this compared to a nanofiltration process integrating the technology developed within LbLBRANE on MF ceramic membranes that avoids the need of a pretreatment process. It has thus been assumed that the outcomes for drinking water production of the LbL technology on the basis of MF ceramic membranes without a pretreatment step can be assimilated to those of the spiral wound thin film composite membranes (NF 270 – FILMTECTM) after the necessary pretreatment processes detailed earlier.
The most relevant outcomes of present case study are summarized next: 1) The use of water treatment membranes manufactured using the LbL deposition of polyelectrolytes on traditionally manufactured MF ceramic membranes does not offer a significant enhancement from the environmental perspective despite the fact that the pretreatment stage has been assumed as unnecessary for the LbL system. In fact, the value of most of the environmental indicators is higher compared to the values of the reference system. 2) The highest environmental impacts are the climate change and fossil depletion. These impacts are closely related to the energy consumption of both systems. 3) If the impacts are analyzed per process in the reference system both operation stages and coagulation process contribute mostly to the selected indicators, being the MF and NF membrane manufacturing and installation construction processes negligible in terms of environmental impact. It is worth highlighting that the MF operation is responsible for the 13% of the impact approximately, and the coagulation for the 24%, while the 54% of the impact is related to NF operation process. In the case of the LbL system, the tendency observed is the same, being the operational stage the major contributor to most indicators (94% of the impacts on average). The impact of these operational stages is mainly related to the energy consumption required. The negative outcome of present assessment is related to the limiting flux in the case of the LbLBRANE Membrane. Furthermore, it should be noticed that the treatment process for sludge generated due to coagulation was not included in the reference system and therefore the environmental impacts associated to this process have not been accounted for.
Case study 3 – Metal recovery, Silicon Carbide membranes - LIQTECH
The functional unit of this study was defined as the treatment of 1 m3 of industrial wastewater at the quality stipulated. A comparative approach of two ultrafiltration processes of industrial wastewater is conducted: the reference system includes the UF silicon carbide membrane manufacturing as well as the installation construction and operation, while the LbL system includes the silicon carbide membrane manufacturing, the LbL coating of the UF membrane, installation construction and operation.
The most relevant outcomes of present case study are summarized next: 1) Unlike the previous case studies, XFLOW and RWB, in the case of LIQTECH the differences between the reference system and the LbL system are negligible. The inventories of both systems are the same, except for polyelectrolytes consumed in the LbL coating. Consequently, the environmental performance of both systems is almost identical. 2) The LbL system is expected to generate a tighter membrane which increases the retention of dissolved substances in wastewater, increasing the quality of the treated water in comparison with LIQTECH’s actual membranes. 3) When analyzing the unit processes, as in the previous case studies, operation stage is the one that produces the highest environmental impacts, due to the energy consumption required.
Task 7.3 Life Cycle Costing (M22-M36)
Task Leader: RWB
A life cycle costing study (LCC) in close combination with a LCA study is an excellent first- tool to determine the feasibility of a possible (industrial-) end product. Especially for an end product business case of which the exact- outcome is very difficult to determine in an early stage of the product development trajectory, an LCC could have an additional value to determine the possible and/or necessary development- and exploitation routes.
Polymer based LbL membrane modules, developed by (lead-) beneficiary B.08 – XFLOW have already been launched, indicating the (commercial-) feasibility of this end product. For ceramic based LbL membrane modules (i.e. lead- beneficiaries B.04 – RWB and B.10 – LIQ), the end product feasibility is not yet that clear.
The major drawback for usage as a LbL support is the (higher-) investment costs (raw materials, membrane production) compared to a polymer support. It was therefore mutually agreed upon to execute a (comprehensive-) LCC study on ceramic based LbL modules.
The applied approach for the determination of the total system costs of the “LbL” system (i.e. LbL membrane modules, ceramic based) included the following costs: Equipment, piping, instrumentation, Control system, control panels, PLC’s, etc.; Project labour fees; Consumable costs; Chemical costs; Energy costs.
The total system costs over a system lifetime of 15 years are a factor 2,24 higher for the “LbL” system compared to the “conventional” system (i.e. pre-treatment: coagulation + ceramic MF, followed by spiral wound polymer NF. The results clearly indicate that the ceramic based LbL membrane module needs to be further developed and/or upgraded to a “second generation” module (i.e. product) in order to overcome the determined higher system total costs factor of 2,24 and hence to end-up with an commercial competitive product for the defined study case.
Module development should be focused on reducing the LbL layer resistance for water permeation and drainage/collection by target engineering of the NF (i.e. “LbL”) top layer, resulting in an enhanced in-field productivity per square meter membrane surface area at a similar or slightly increased trans membrane differential pressure operation.
Potential Impact:
Potential impact
The Layer-by-Layer (LbL) production technique, to prepare low pressure nanofiltration (NF) membranes from water soluble polyelectrolyte (PE) solutions, compared to the conventional thin film composite (TFC) technique is of major importance due to the REACH regulation. Using organic solvents such as hexane in the TFC production is a major problem due to the REACH regulation, therefore it is necessary to provide a method, which is environmentally friendly (water based) and has thus a high socio-economic effect on the society due to the LbLBRANE project.
Removing endocrine substances (EDC) from surface water with LbL membranes compared to conventional filtration systems is of further interest. The contributions of this project to the scientific, social and economic improvements of the EU are of major importance. Endocrine substances in our drinking water, which pollute our resources have to be removed to maintain a high quality drinking water stream. The membrane system, developed in the LbLBRANE project has major economical (no solvents, easy applicable, stable for harsh cleaning conditions, low cost, regenerable under mild and environmentally conditions, high performance and extended lifespan) and therefore social advantages compared to conventional treatment systems.
The main difference between the LbL system and the conventional NF or reverse osmosis (RO) system is the ability of the LbL system to use a membrane with comparable retentions than mentioned before, but to use a membrane, which impact on the environment, due to its production method and the tailor made purpose, is beneficiary to the conventional systems. These statements are also supported by the life cycle assessment (LCA) performed during the project. Furthermore, conventional system, even RO systems have big problems with the separation of the endocrine compounds because a lot of them are very hydrophilic, which means the endocrines get recognized by the membrane likely as water. Conventional systems separate on solution-diffusion mechanism and let water pass through the membrane because of its high affinity to water. When the endocrine materials are now recognized comparable to water, they can easily pass the membrane together with the water; therefore the removal rate of endocrine substances is limited. Introducing charge, with the LbL system, kept the retention constant, while improving the flux through the membrane. This reduces the amount of modules needed and is beneficiary for the industry by reducing operational and capital expenses.
The new water framework and the RIVM Report 703719064/2010 strongly define the awareness of emerging contaminants in European surface water and show the need for new techniques to remove micro-pollutants. The water framework shows that safe drinking water is the backbone of social and economic live in the world.
If this legislation would be defined European wide, the market potential for this kind of new developments would be large, because of the involvement of Municipal and private authorities. But, this legislation is not clear at the moment, and this is the biggest risk for a membrane producer at the present time. It is not known yet, if and when this legislation will be introduced. Up to then, no one will introduce this new and mainly more expensive technique to remove these contaminants from drinking water sources.
For the participation in an FP7 project like this it is important that large companies, as Pentair X-Flow, to deal with these uncertainties. First of all it is important to build up a strategy on broad product diversity. It is important to sell products not only in the same market (water-beverage), to have a broad spectrum of products (micro-, ultra- and nanofiltration) and to produce products from environmentally friendly sources (e.g. PE’s in water). The last point strongly fits into Pentair X-Flows strategy and therefore participating in LbLBRANE was a low risk for the company. Therefore risk analysis of these projects, in which fundamentally new products are developed, is of major importance.
Concluding, the LbLBRANE project delivered a substantial contribution to the problems of safe and healthy drinking water in the European Union, but also worldwide. This technology development strengthens the pioneering role of the EU in a healthy mankind, the most important fact in human life.
Dissemination activities
LbLbRANE was very active within the Nano4Water cluster which was one of the main dissemination activities for the project. During the three years of the project we participated on every cluster meeting with several oral and poster contributions. Furthermore on the last meeting in January 2015 LbLBRANE organized a demonstrator to present our achievements. Therefore we hired a 2 times 4 m booth; brought 2 distinguish setups and demonstrated the simplicity and effectiveness of LbL technology on membranes. In addition we created 5 posters showing the structure of the project and the major results we could achieve during the project time.
Furthermore the coordinator, John Erik Wong, visited several conferences in the field of membrane technology and LbL technology to present LbLBRANE to a wide audience with different backgrounds. In total, the complete consortium contributed with 30 oral presentations and 20 poster presentations at different scientific workshops and conferences. Furthermore 7 peer reviewed articles are already published and several more are in preparation and will be published soon.
All dissemination activities regarding the LbLBRANE project have been regularly updated on the project website (www.lblbrane.eu) during its lifespan and will be maintained until 2022.
Exploitation of results
XFLOW commercialized already one product and will enter the market with different products in the future. The consortium and explicit XFLOW decided that patenting at this stage is not a good strategy to pursue. A patent violation from other competitors cannot be identified easily since the LbL film itself is just a few nanometre thick. Thus a visual investigation is more or less impossible. The amount of parameters needed to be controlled for an effective coating is rather high and hence a patent would reveal too much important information that the project hardly identified. With this information a competitor can develop a product quite fast. By varying one of the parameters slightly this product would even not violate any possible patent. Thus it was decided that a trade secret is for this type of foreground the better alternative.
In case of the ceramic membranes further developing and especially upscaling is needed for a successful commercialization. Although the permeability of ceramic LbL membranes is as good as the one of polymeric LbL membranes or classical nanofiltration membranes, it is for this type of membrane too low for a successful implementation on the market. The ceramic support itself is simply too expansive and thus the developed membranes are for standard application such as drinking water productions not competitive. However, niche markets with extraordinary requirements in stability, are from great interest for the developed membranes. In additions unique selling points such as the possibility of fully regeneration or the option to implement a coagulant free filtration process with these membranes will draw the interest in the future.
List of Websites:
www.lblbrane.eu
Contact details: John Erik Wong: john.wong@avt.rwth-aachen.de Daniel Menne: +49 241 80 29948 daniel.menne@avt.rwth-aachen.de