Spiral Wound Membrane Modules Research Articles

Effect of ultrafiltration membranes properties and channel configuration on membrane fouling and performance

The work describes the existing views on colloidal, suspended and organic fouling in ultrafiltration (UF) membrane modules using for natural water treatment. The paper presents the results of the experimental research allowing for a quantitative determination of sorption and plugging rates, and for evaluation of their effect on membrane performance loss over time. Small colloidal particles pose a risk to UF unit due pore plugging; especially when membranes treat water with a very low content of suspended solids. This effect often cannot be detected during short-time pilot tests, but it can have a decisive influence on the operation of a membrane unit. Study of the filterability characteristic of water contaminants enables us to forecast the filtration type on UF membranes and to evaluate their performance losses. The paper also describes the effect of a feed channel structure – in particular, a presence of a feed spacer in spiral wound membrane modules – on channel hydraulic resistance growth. The technique of channel resistance estimation, depending on suspended particles concentration in the source water, is presented.

Construction and validation of a long-channel membrane test cell for representative monitoring of performance and characterization of fouling over the length of spiral-wound membrane modules

The authors thank the German Federal Ministry of Education and Research (BMBF) for the financial support of the project “Fouling minimized reclamation of secondary effluents with Reverse Osmosis” (ReSeRO) under grant no. 02WA1076. Further, several people have given time and efforts on discussion of the introduced topic and are thus thanked Mr. A. Lerch (Chair of Water Supply Engineering, TU Dresden, Germany) for stimulating suggestions during the construction of the LCMTC, Mrs. J. Bruckner, Mr. G. Orzechowski and Mr. D. Diersche (Chair of Water Supply Engineering, TU Dresden, Germany) for their help regarding analysis and support on the setup of the test rig, respectively, Mr. D. Kreutzmann and Mr. M. Meinel for discussions on material strength and tensions, Mr. J. Friedrich (Institute of Lightweight Engineering and Polymer Technology, TU Dresden) for the supply of the PMMA model calculation on material strength and Mr. S. Bucs (KAUST) for his help with the Rhodamine B experiment.

Characterization of feed channel spacer performance using geometries obtained by X-ray computed tomography

Spiral-wound membrane modules used in water treatment for water reuse and desalination make use of spacer meshes for keeping the membrane leaves apart and for enhancing the mass transfer. Computational fluid dynamics (CFD) has gained importance in the design of new spacers with optimized hydrodynamic characteristics, but this requires a precise description of the spacer geometry. This study developed a method to obtain accurate three-dimensional (3-D) geometry representations for any given spacer design from X-ray computed tomography (CT) scans. The method revealed that the filaments of industrial spacers have a highly variable cross-section size and shape, which impact the flow characteristics in the feed channel. The pressure drop and friction factors were calculated from numerical simulations on five commercially available feed spacers used in practice. Model solutions compared well to experimental data measured using a flow cell for average velocities up to 0.2m/s, as used in industrial reverse osmosis and nanofiltration membrane operations. A newly-proposed spacer geometry with alternating strand thickness was tested, which was found to yield a lower pressure drop while being highly efficient in converting the pumping power into membrane shear. Numerical model solutions using CFD with geometries from CT scans were closer to measurements than those obtained using the traditional circular cross-section strand simplification, indicating that CT scans are very well suitable to approximate real feed spacer geometries. By providing detailed insight on the spacer filament shape, CT scans allow better quantification of local distribution of velocity and shear, possibly leading to more accurate estimations of fouling and concentration polarization.

Spatial heterogeneity of biofouling under different cross-flow velocities in reverse osmosis membrane systems

The spatially heterogeneous distribution of biofouling in spiral wound membrane systems restricts (i) the water distribution over the membrane surface and therefore (ii) the membrane-based water treatment. The objective of the study was to assess the spatial heterogeneity of biofilm development over the membrane fouling simulator (MFS) length (inlet and outlet part) at three different cross-flow velocities (0.08, 0.12 and 0.16m/s). The MFS contained sheets of membrane and feed spacer and simulated the first 0.20m of spiral-wound membrane modules where biofouling accumulates the most in practice. In-situ non-destructive oxygen imaging using planar optodes was applied to determine the biofilm spatially resolved activity and heterogeneity.Comparison of the inlet and outlet position of the MFS showed a more (i) heterogeneous biofilm distribution and a (ii) higher biological activity at the inlet side (first 2.5cm) for all cross-flow velocities. The lowest cross-flow velocity had the highest biomass activity particularly at the inlet side. A better characterization of biofilm development, including the factors that influence the biofilm spatial heterogeneity in membrane systems with time, may help to develop effective strategies for biofouling control in membrane systems.

3D printing by selective laser sintering of polypropylene feed channel spacers for spiral wound membrane modules for the water industry

ABSTRACTFeed spacers are net-like structures present in spiral wound membrane modules (SWM) used for treatment of water and wastewater. Feed spacers require appropriate stiffness to support the membrane sheets without damaging and puncturing the membrane surfaces. They also need to be flexible enough to be rolled up around the central permeate tube forming the SWM. Polypropylene (PP) is the commercially used material for feed spacers due to its flexibility and excellent chemical resistance properties. In this paper, selective laser sintering (SLS) is used to investigate the printability of net-typed structures using PP materials to represent feed spacers. SLS processing parameters such as layer thickness, part bed temperature, energy density and scan pattern were studied and net-typed PP spacers were successfully fabricated. However, an analysis on tensile test and dimensional accuracy shows that Young’s modulus of the PP material tends to be correlated to the accuracy of the dimensions of the net-typed spacer prototypes.

Modeling, control, and dynamic performance analysis of a reverse osmosis desalination plant integrated within hybrid energy systems

An RO (reverse osmosis) desalination plant is proposed as an effective, FLR (flexible load resource) to be integrated into HES (hybrid energy systems) to support various types of ancillary services to the electric grid, under variable operating conditions. To study the dynamic analysis of such system, special attention is given here to the detailed dynamic modeling and control design of RO desalination process that employs a spiral-wound membrane module. In particular, the solution-diffusion model modified with the concentration polarization theory is applied to predict RO performance over a large range of operating conditions. Simulation results involving several case studies suggest that an RO desalination plant can provide operational flexibility to participate in energy management at the utility scale by dynamically optimizing the use of excess electrical energy. The incorporation of additional commodity (fresh water) produced from a FLR allows a broader range of HES operations for maximizing overall system performance and profitability.

Theoretical Considerations of Pressure Drop and Mass Transfer of Gas Flow in Spiral Wound Membrane Modules

In this work we give the preliminary results of the development of two reliable correlations for the calculation of the friction and mass transfer coefficients for the gas transfer through spiral wound membrane modules. The mass transfer coefficient which allows determining the polarization phenomenon was taken in consideration through the calculation of the Sherwood number near the surface of the membranes. Both correlations take in consideration the inclination angle of transversal and longitudinal filaments of grids in spacers. They allow a good prediction of the pressure drop, friction coefficient and the mass transfer in spiral modules for gas flow when compared with experimental results obtained in a previous work reported in the literature.

Theoretical Considerations of Pressure Drop and Mass Transfer of Gas Flow in Spiral Wound Membrane Modules

Theoretical Considerations of Pressure Drop and Mass Transfer of Gas Flow in Spiral Wound Membrane Modules

Pressure retarded osmosis: A membrane process for environmental sustainability

Salinity Gradient Power (SGP) based on the controlled mixing between two solutions at different salinities is a viable alternative to produce power from renewable sources. Pressure Retarded Osmosis (PRO) is one of the most promising technologies proposed so far for the exploitation of such energy source. Apart from the typical source of salinity gradients, namely river water and seawater, more and more interest has been raised recently towards the use of non-conventional saline solutions. In this work, water originating from a sewage treatment plant is used as the dilute solution (feed solution), while brine exiting from a desalination plant is used as the concentrate (draw solution), thus being efficiently diluted before the discharge into the sea. Aim of this work is to investigate the performance of PRO modules arranged in series via a purposely developed process model based on transport and balance equations. Detrimental effects due non-ideal phenomena as salt diffusion through the membrane, concentration polarization were taken into account. Pumping power was also accounted for. Geometrical data were derived from existing spiral wound membrane modules typically employed in Reverse Osmosis. The effect of solution velocity, number of PRO units and operative hydraulic pressure (applied on the draw solution channel) on the process performance was investigated. Results show that the dependence of the net power on velocity and applied pressure is not monotonic thereby exhibiting a maximum: under optimized conditions, a maximum net power of ~1.5kW corresponding to a net power density of ~6.6 W/m 2 can be obtained with six identical PRO modules. Along with this power production, a simultaneous brine dilution of more than 22% was found at the same conditions. However, despite the potential shown by the model, the main limitation for a real process might be the real performances of the osmotic membranes in terms of mechanical robustness and resistance against fouling phenomena. In this regard, valuable contributions may come from nanotechnologies ad-hoc developed.

High Total Dissolved Solids Water Treatment by Charged Nanofiltration Membranes Relating to Power Plant Applications.

Selective desalination through nanofiltration (NF) is of great interest for many industrial applications including reuse of power plant scrubber wastewater and treatment of water containing high concentrations of TDS (total dissolved solids). This work seeks to understand the effect ion interactions at the membrane interface have on rejection and flux performance of charged NF membranes. NF membranes were also effective for low energy desalination of scrubber wastewater from Georgia Power Plant Bowen, composed primarily of Ca2+, Mg2+, Cl-, and SO4 2-. As NF membranes have the capability for selective separations, 80% water recovery was achieved experimentally while maintaining an overall rejection of over 60% for Ca2+ and Cl-. The occurrence of CaSO4 precipitation at high water recovery was observed. The effect of precipitation on osmotic pressure and the effect of Cl- counterions on increasing gypsum solubility were explored for water recovery operation. This work expands on a previous work on the topics of desalination of multi-ionic solutions by incorporating the use of large scale membrane modules (0.59 m2) with several synthetic solutions as well as actual scrubber water containing precipitating elements, Ca2+ and SO4 2-. It was observed that the spiral wound membrane modules maintained a stable water permeability over the 144 day course of tests.

Multi-scale modelling of OSN batch concentration with spiral-wound membrane modules using OSN Designer

Three commercial spiral-wound membrane modules of different sizes, from 1.8″×12″ to 4.0″×40″, are used to concentrate a solution of sucrose octaacetate in ethyl acetate under different operating conditions. A mathematical model to describe the batch concentration process is developed, based on a combination of the classical solution diffusion membrane transport model and the film theory, to account for the mass transfer effects. The model was implemented using the “OSN Designer” software tool. The membrane transport model parameters as well as all parameters in the pressure drop and mass transfer correlations for the spiral-wound modules were obtained from regression on a limited number of experimental data at steady state conditions. Excellent agreement was found between the experimental and multi-scale modelling performance data under various operating conditions. The results illustrate that the performance of a large scale batch concentration process with spiral-wound membrane modules can be predicted based on laboratory crossflow flat sheet test data when the fluid dynamics and mass transfer characteristics in the module, and the necessary channel geometry are known. In addition, the effects of concentration polarisation, pressure drop through feed and permeate channels, and thermodynamic non-ideality of the solution at large scale batch concentration are also investigated.

A pilot-scale forward osmosis membrane system for concentrating low-strength municipal wastewater: performance and implications.

Recovery of nutrients and energy from municipal wastewater has attracted much attention in recent years; however, its efficiency is significantly limited by the low-strength properties of municipal wastewater. Herein, we report a pilot-scale forward osmosis (FO) system using a spiral-wound membrane module to concentrate real municipal wastewater. Under active layer facing feed solution mode, the critical concentration factor (CCF) of this FO system was determined to be 8 with 0.5 M NaCl as draw solution. During long-term operation at a concentration factor of 5, (99.8 ± 0.6)% of chemical oxygen demand and (99.7 ± 0.5)% of total phosphorus rejection rates could be achieved at a flux of 6 L/(m2 h) on average. In comparison, only (48.1 ± 10.5)% and (67.8 ± 7.3)% rejection of ammonium and total nitrogen were observed. Cake enhanced concentration polarization is a major contributor to the decrease of water fluxes. The fouling also led to the occurrence of a cake reduced concentration polarization effect, improving ammonium rejection rate with the increase of operation time in each cycle. This work demonstrates the applicability of using FO process for wastewater concentrating and also limitations in ammonium recovery that need further improvement in future.

Experimental and numerical characterization of the water flow in spacer-filled channels of spiral-wound membranes

Micro-scale flow distribution in spacer-filled flow channels of spiral-wound membrane modules was determined with a particle image velocimetry system (PIV), aiming to elucidate the flow behaviour in spacer-filled flow channels. Two-dimensional water velocity fields were measured in a flow cell (representing the feed spacer-filled flow channel of a spiral wound reverse osmosis membrane module without permeate production) at several planes throughout the channel height. At linear flow velocities (volumetric flow rate per cross-section of the flow channel considering the channel porosity, also described as crossflow velocities) used in practice (0.074 and 0.163 m·s−1) the recorded flow was laminar with only slight unsteadiness in the upper velocity limit. At higher linear flow velocity (0.3 m·s−1) the flow was observed to be unsteady and with recirculation zones. Measurements made at different locations in the flow cell exhibited very similar flow patterns within all feed spacer mesh elements, thus revealing the same hydrodynamic conditions along the length of the flow channel. Three-dimensional (3-D) computational fluid dynamics simulations were performed using the same geometries and flow parameters as the experiments, based on steady laminar flow assumption. The numerical results were in good agreement (0.85–0.95 Bray–Curtis similarity) with the measured flow fields at linear velocities of 0.074 and 0.163 m·s−1, thus supporting the use of model-based studies in the optimization of feed spacer geometries and operational conditions of spiral wound membrane systems.

Predictive pressure drop models for membrane channels with non-woven and woven spacers

Predictive pressure drop models have been identified for membrane channels with both woven and non-woven spacers as found in plate and frame or spiral wound membrane modules. The models allow for the first time the thorough quantitative description of the pressure drop for a wide range of design parameters specifying the thickness and orientation of the spacer filaments. A systematic work flow has been developed efficiently integrating detailed computational fluid dynamics (CFD) simulations on high-performance computing (HPC) systems with established optimization-based model identification methods. The work-flow efficiently handles the complexity arising from the large number of design parameters and allows for the model identification with minimal number of CFD simulations. The resulting models facilitate for the first time a thorough sensitivity analysis of the pressure drop with respect to all important design parameters elucidating strongly nonlinear patterns in the sensitivities. This indicates that the generalization of trends from a small number of CFD simulations, frequently used in previous work to simplify the spacer design problem, can yield inaccurate results.

Characterization of membrane fouling distribution in a spiral wound module using high-frequency ultrasound image analysis

The fouling phenomenon in spiral wound membrane modules was investigated using ultrasonic time domain reflectometry (UTDR) and computational fluid dynamic (CFD) simulations. This study utilized a high-frequency 50-MHz ultrasound system to measure the fouling distribution in the spiral wound ultrafiltration and reserve osmosis membrane modules. The results show that for a porous membrane, the voltage decreases as the fouling increases while the opposite is true for a dense membrane. The effects of gravity and module orientation on fouling were also investigated. It is clear from the results that gravity and membrane curvature play a role in the deposition of foulants on the membrane surface. This finding is supported by CFD simulations revealing that the inner membrane experiences higher axial velocities as the fluid flows through the spacers, thus generating a higher wall shear stress in the interior, which can aid in reducing membrane fouling. This study demonstrated that UTDR with a high-frequency transducer can be used to analyze the fouling phenomenon in spiral wound membrane modules.

Performance of spiral-wound membrane modules in organic solvent nanofiltration – Fluid dynamics and mass transfer characteristics

During the past few decades organic solvent nanofiltration has received a great deal of attention and a growing number of studies has been reported on development and optimisation of solvent resistant membranes and their transport mechanism. However, most of these studies have used flat sheet membranes. On the other hand, many researchers studied fluid dynamics and mass transfer in spiral-wound membrane modules, almost exclusively in aqueous solutions. This paper reports the performance of four spiral-wound membrane modules tested in 0–20wt% solutions of sucrose octaacetate in ethyl acetate under various pressures and retentate flowrates. These modules were made of two different types of membranes (a commercial membrane, PuraMem® S600, and a development product, Lab-1, from Evonik Membrane Extraction Technology Limited) and covered three module sizes (1.8″×12″, 2.5″×40″ and 4.0″×40″). All modules had the same feed and permeate spacers. The classical solution diffusion model was applied to describe the transport of solute and solvent through the membrane and regress the unknown model parameters from flat sheet data. Correlations for characterising the fluid dynamics and mass transfer in the spiral-wound membrane modules, as well as the parameters describing the feed and permeate channels, were determined by performing the regression of experimental data of a 1.8″×12″ PuraMem® S600 membrane module. The classical solution–diffusion model, combined with the film theory, was then successfully applied to predict the performance of other modules of larger size (such as the 2.5″×40″ and 4.0″×40″ module sizes) and/or made of a different membrane material (such as Lab-1). The procedure proposed in this paper predicts the performance of a specific module by obtaining a limited number of experimental data for flat sheets and a 1.8″×12″ spiral-wound membrane module only (necessary to obtain the fitting parameters characteristic of the membrane and the module). Furthermore, with this procedure, it is not necessary to know a priori the spacer geometry, because the necessary information about the spacer geometry will be also obtained by regression of few experimental data.

Preparation and characterization of ZSM-5/PDMS hybrid pervaporation membranes: Laboratory results and pilot-scale performance

ZSM-5 zeolites/Polydimethylsiloxane (PDMS) hybrid membranes were prepared and subsequently applied in ethanol recovery from an ethanol–water mixture by pervaporation (PV) using a pilot-plant with spiral-wound membrane module. The influences of calcination temperature on PV performances as well as zeolites properties were studied. Meanwhile, the optimum zeolites loading was turned out to be 30wt%, the SEM indicated that ZSM-5/PDMS was coated uniformly on the surface of porous PVDF substrate, and the separation layer was dense with the thickness of 8.9μm. The effects of feed temperature and feed flow velocity on the performance of the pilot-scale PV system were investigated. It was found that with increasing feed temperature, the permeation flux increased, whereas the separation factor firstly increased, then it decreased rapidly. As the feed flow velocity increased, both the permeation flux and separation factor increased. Under the optimum process conditions, the pilot-plant showed a total flux of 1170g/m2h with ethanol concentration of 60.00wt% at a feed temperature of 60°C, a feed flow velocity of 3.2cm/s and a permeation side pressure of about 2300Pa with a feed concentration of 10.0wt% ethanol. A long term run consisted of 1000h of continuous PV experiments exhibited satisfying performance stability, indicating that the pilot-plant was a promising approach to separate ethanol from ethanol–water mixture and had long-term stability required for industrial application.

Diffusion dialysis of sulfuric acid in spiral wound membrane modules: Effect of module number and connection mode

The main goal of this work is to explore the transfer of sulfuric acid in spiral wound membrane modules. The effect of various parameters such as connection modes, number of membrane modules, flow rate and initial feed concentration are fully investigated. The results show that the acid recovery ratio increases with the number of membrane modules and decreases with the flow rate but does not apparently changes with the initial feed concentration. Meanwhile, both the recovered acid concentration and the dialysate acid concentration are directly proportional to the feed concentration for different number of SWDD modules. For double SWDD membrane module system, the mode D-d (series connection in both acid side and water sides) seems to be the best one from the integrated viewpoints of acid recovery ratio and recovered acid concentration. For multi-modules system, the treating capacity is much higher than the sum contributed from each single module.

Experiment and modeling for performance of a spiral-wound pressure-retarded osmosis membrane module

Pressure-retarded osmosis (PRO) process utilizes the transport of water through a semipermeable membrane to generate electricity from salinity gradient resources. Recent PRO research has shown the feasibility of PRO technologies in laboratory-scale experiments, but there is currently a lack of experimental pilot-scale investigations to ensure the success of PRO technology. This study was conducted to predict the power density of a PRO module using PRO membrane transport properties such as water permeability, salt permeability, and membrane structure parameter. The performance of an 8040 spiral-wound PRO module was experimentally investigated, and the results were compared with the simulated prediction. The maximum power density of the investigated PRO module was 1.8 W m−2 at 10.4 bar using 35 g L−1 of NaCl as a draw solution. At the outlet of the module, the concentration changes of the draw and feed solutions were observed, suggesting a gradual decrease of membrane power density inside the PRO module. The simulation model, which considered concentration changes of draw and feed solutions, reverse salt flux, and mass transport coefficient inside the module, closely estimated the performance of the PRO module. However, the model overestimated the power density at high hydraulic pressure difference. It was concluded that severe increase of reverse salt flux at a high hydraulic pressure difference negatively contributed to the performance of the PRO module.

Early non-destructive biofouling detection in spiral wound RO membranes using a mobile earth׳s field NMR

We demonstrate the use of Earth׳s field (EF) Nuclear Magnetic Resonance (NMR) to provide early non-destructive detection of active biofouling of a commercial spiral wound reverse osmosis (RO) membrane module. The RO membrane module was actively biofouled to different extents, by the addition of biodegradable nutrients to the feed stream, as revealed by a subtle feed-channel pressure drop increase. Easily accessible EF NMR parameters (signal relaxation parameters T1, T2 and the total NMR signal modified to be sensitive to stagnant fluid only) were measured and analysed in terms of their ability to detect the onset of biofouling. The EF NMR showed that fouling near the membrane module entrance significantly distorted the flow field through the whole membrane module. The total NMR signal is shown to be suitable for non-destructive early biofouling detection of spiral wound membrane modules, it was readily deployed at high (operational) flow rates, was particularly sensitive to flow field changes due to biofouling and could be deployed at any position along the membrane module axis. In addition to providing early fouling detection, the mobile EF NMR apparatus could also be used to (i) evaluate the production process of spiral wound membrane modules, and (ii) provide an in-situ determination of module cleaning process efficiency.