Flat Sheet Membrane Module Research Articles

Desalination of Highly Saline Water Using Direct Contact Membrane Distillation (DCMD)

In this work, laboratory experiments were carried out to verify direct contact membrane distillation system’s performance in highly saline water desalination. The study included the investigation of various operating conditions, like feed flow rate, temperature and concentration of NaCl solution and their impact on the permeation flux were discussed. 16 cm2 of a flat sheet membrane module with commercial poly-tetra-fluoroethylene (PTFE) membrane, which has 0.22 μm pore size, 96 µm thickness and 78% average porosity, was used. A high salt rejection factor was obtained greater than 99.9%, and the permeation flux up to 17.27 kg/m2.h was achieved at 65°C for hot feed side and 20°C for cold side stream.

Characterization of a New Flat Sheet Membrane Module Type for Gas Permeation

AbstractModern high‐performance flat sheet gas separation membranes exhibit high permeances as well as high selectivities, e.g., for CO2 separation. Novel membrane modules are desirable to transfer the intrinsic membrane performance to the process. The introduced module implements countercurrent flow, which allows for the best utilization of the required driving force, provided concentration polarization and pressure drops can be kept at bay. As such, it is different from established flat sheet modules for gas separation. The design features allow for straightforward scaling and easy adjustment to other operating conditions. During module development equation‐oriented modeling, computer‐aided engineering design and application of computational fluid dynamics for flow optimization were integrated. The prototype was investigated in a pilot plant. The experimental results reflected the simulation predictions and proved the validity of the module concept.

Anaerobic Membrane Bioreactor (AnMBR) for the Treatment of Cheese Whey for the Potential Recovery of Water and Energy

A single-stage Anaerobic Membrane Bioreactor (AnMBR) for the treatment of cheese whey and its co-digestion with cattle slurry was investigated with the aim of potentially recovering water and energy from the wastewater. A 9 L reactor coupled to an ultrafiltration flat sheet membrane module in an external configuration was employed. This configuration enabled the proper separation of solids from permeate. Cheese whey was stored at room temperature and its chemical oxygen demand (COD) varied between 51 and 80 g/L. The reactor was operated at an average hydraulic retention time (HRT) of 15 days and at an organic loading rate (OLR) of 1.2–8.4 kg COD/(m3·day). During operation a COD removal average of 91% ± 7% was achieved. The biogas production ranged from 0.2 to 0.9 m3 biogas/kg COD removed and its methane content was 51–73%. From these results, a potential energy recovery of 2.4 kWh/kg COD removed was calculated. Microbial community analysis showed that bacteria belonging to the orders Bacteroidales and Clostridiales became the most prevalent. The bioreactor was dominated by acetotrophic methanogenesis. The co-digestion of cheese whey with cow manure (3:1) did not decrease NaOH consumption for pH control. Water reuse for cleaning purposes is possible if permeate pH is maintained at 6. Prior to the scaling-up of the system, a pilot scale test would be necessary to optimise membrane performance. The use of AnMBR technology at a real scale would be appropriate since it is a compact technology which permits both energy and potential water recovery after permeate post-treatment, thus constituting a further step towards the establishment of a broader a circular economy approach.

Experimentally-validated computational simulation of direct contact membrane distillation performance

A Direct Contact Membrane Distillation system using a flat-sheet membrane module was fabricated to experimentally study the effects of operating conditions (inlet temperatures and flow rates of feed and permeate streams and salt concentration) on its distilled water production. A two-dimensional Computational Fluid Dynamics (CFD) model considering transmembrane mass flux and heat conduction and associated phase change heat transfer (evaporation and condensation) was developed. It was found that the computational predictions of distilled water production agreed well with the experimental measurements. Furthermore, the CFD model analyzed the effects of filament spacing of a screen spacer in the flow channels and flow configuration (counterflow and parallel) on the water distillation performance. In this study, it is concluded that high water distillation is achieved by using low permeate temperature, high feed temperature, high feed and permeate flow rates, and less salt concentration in a counterflow configuration. The water distillation is more influenced by the feed temperature than the permeate temperature due to the water saturation pressure-temperature relation. The simulation results also showed that the convection thermal resistances in the feed and permeate channels are decreased by using screen spacers and therefore, the temperature and concentration polarization effects are decreased in the channels.

The application of the radiotracer method for the investigation of the cake layer formation on the membrane surface in the cross-flow flat-sheet membrane module

The application of the radiotracer method for the investigation of the cake layer formation on the membrane surface in the cross-flow flat-sheet membrane module

The use of ultrasound to reduce internal concentration polarization in forward osmosis

Unlike reverse osmosis (RO) that is dominated by the hydraulic pressure differential, forward osmosis (FO) uses the osmotic pressure gradient as the driving force between a dilute feed solution and a concentrated draw solution across a membrane. High pressure is not required in FO, which means that FO can be used as an alternative to RO as an energy-saving separation process in desalination technology. However, a major limiting factor of the FO process is the internal concentration polarization (ICP). Because of the stagnant environment inside the porous supporting layer of a FO membrane, it is difficult to mitigate the ICP by simply increasing the shear stress or promoting turbulence. In this study, the ICP is reduced by ultrasound. The effect of the ultrasound frequency and output power on the ICP coefficient is investigated in a flat-sheet FO membrane module with counter-current flow. The ultrasound frequency and output power are varied between 25, 45, and 72 kHz and over the range of 10–70 W, respectively. NaCl solution is used as both the feed and draw solution. The results illustrate that moderate ultrasonic irradiation is effective for reducing the ICP in a FO process. A modified solution–diffusion model based on film theory is used to assess the effect of ultrasound on the ICP in a FO process. The ICP coefficient is estimated using this model.

Development of CO 2 Selective Poly(Ethylene Oxide)-Based Membranes: From Laboratory to Pilot Plant Scale

Membrane gas separation is one of the most promising technologies for the separation of carbon dioxide (CO2) from various gas streams. One application of this technology is the treatment of flue gases from combustion processes for the purpose of carbon capture and storage. For this application, poly(ethylene oxide)-containing block copolymers such as Pebax® or PolyActive™ polymer are well suited. The thin-film composite membrane that is considered in this overview employs PolyActive™ polymer as a selective layer material. The membrane shows excellent CO2 permeances of up to 4 m3(STP)·(m2·h·bar)−1 (1 bar = 105 Pa) at a carbon dioxide/nitrogen (CO2/N2) selectivity exceeding 55 at ambient temperature. The membrane can be manufactured reproducibly on a pilot scale and mounted into flat-sheet membrane modules of different designs. The operating performance of these modules can be accurately predicted by specifically developed simulation tools, which employ single-gas permeation data as the only experimental input. The performance of membranes and modules was investigated in different pilot plant studies, in which flue gas and biogas were used as the feed gas streams. The investigated processes showed a stable separation performance, indicating the applicability of PolyActive™ polymer as a membrane material for industrial-scale gas processing.

Theoretical and experimental study of the ammonia/water absorption process using a flat sheet membrane module

A hydrophobic microporous membrane contactor was proposed and studied as an absorber for an ammonia/water absorption cycle. The heat and mass transfer process in the adiabatic flat sheet membrane module was investigated experimentally and analytically. For the experimental study, a membrane absorber test bench was designed and built. Moreover, a unidimensional model was developed and validated with the experimental results. The influence of the temperature, concentration, flow rate and membrane characteristics on the absorption process was evaluated. For the conditions considered in this study, the results indicate that the absorption flux is clearly governed by the mass transfer in the liquid phase. The maximum absorption flux was 4.7·10−3kg/m2s with a solution flow rate of 45kg/h. According to the model, the hydrophobic membrane should be as thin as possible and the pore diameter between 0.03μm and 0.10μm.

Use of a ceramic membrane bioreactor (CMBR) to treat wastewater at Guilin University of Technology

A ceramic membrane bio-reactor (CMBR) process was first used to treat wastewater collected from a campus of Guilin University of Technology (GUT). A CMBR with a submerged flat-sheet ceramic membrane module was designed for a Qmax of 300 m3/d. With a stable flux at about 33 L/m2 h, the transmembrane pressure was maintained at −10 kPa until the end of the experiment. The results showed that the CMBR process is a robust system capable of producing high-quality service water from campus wastewater. By using the CMBR process, the treated water met the Chinese national standards for landscaping irrigation.

Wear Characterization of High Temperature Oxidized Ni Based Superalloys

Objectives: This work presents a study of the effect of membrane surface with dimples on the heat transfer in vacuum membrane distillation (VMD). Methods/Statistical Analysis: Polyvinylidene fluoride (PVDF) membrane and distilled water as feed solutions are tested in a laboratory-scale cross-flow flat-sheet membrane module with membrane area of 72.4 cm2. A perforated aluminum support embedded in the permeate compartment is used to support the membrane during the VMD process. Findings: The results show that the dimples stamped on the membrane surface by the perforated support having the diameter and depth approximately 5 and 1 mm, respectively. The permeability of the membrane with dimples increases by 3 - 20% at the corresponding feed temperature of 75 - 95°C. The deviations between the heat transfer coefficients predicted by a Nusselt correlation with dimpled effect and the experimental values are less than 10%. Application/Improvements: These findings are significant to reveal the influence of membrane deformation effect on the heat transfer correlation which is used to predict the VMD flux.

Application of quorum quenching bacteria entrapping sheets to enhance biofouling control in a membrane bioreactor with a hollow fiber module

Quorum quenching (QQ) has been recognized as an innovative approach for biofouling control in membrane bioreactors (MBRs). Recently, QQ bacteria entrapping beads (QQ-beads) have been developed and verified to have excellent anti-biofouling potential in a pilot-scale MBR with flat-sheet membrane modules. In this study, considering the dense structure of hollow fiber (HF) bundles into which QQ-beads can hardly penetrate, QQ bacteria entrapping sheets (QQ-sheets) were developed as a new shape of QQ-media suitable for MBRs with HF modules. In a lab-scale MBR, QQ-sheets with a thickness of 0.5mm exhibited a greater physical washing effect than did QQ-beads with a diameter of 3.5mm because the former collided with membrane surfaces at the inner as well as the outer part of HF bundles, whereas the latter only made contact with the outer part. Moreover, QQ-sheets showed 2.5-fold greater biological QQ activity than did QQ-beads due to their greater total surface area at a fixed volume of QQ-media. These results suggest high potential for QQ-sheets to be used in MBRs with HF modules.

Effect of the Shape and Size of Quorum-Quenching Media on Biofouling Control in Membrane Bioreactors for Wastewater Treatment.

Recently, spherical beads entrapping quorum quenching (QQ) bacteria have been reported as effective moving QQ-media for biofouling control in MBRs for wastewater treatment owing to their combined effects of biological (i.e., quorum quenching) and physical washing. Taking into account both the mass transfer of signal molecules through the QQ-medium and collision efficiencies of the QQ-medium against the filtration membranes in a bioreactor, a cylindrical medium (QQ-cylinder) was developed as a new shape of moving QQ-medium. The QQ-cylinders were compared with previous QQ-beads in terms of the QQ activity and the physical washing effect under identical loading volumes of each medium in batch tests. It was found that the QQ activity of a QQ-medium was highly dependent on its specific surface area, regardless of the shape of the medium. In contrast, the physical washing effect of a QQ-medium was greatly affected by its geometric structure. The enhanced anti-biofouling property of the QQ-cylinders relative to QQ-beads was confirmed in a continuous laboratory-scale MBR with a flat-sheet membrane module.

Ultrafiltration of Cherry Concentrate Under Ultrasound with Carbonated Feed as a New Fouling Control Method

In this study, the effects of ultrasound (US) with carbonated feed were studied on ultrafiltration flux enhancement and membrane hydrodynamic resistances. A cross flow ultrafiltration of cherry concentrate was performed under US at 37 and 80 kHz with carbonated feed and noncarbonated feed, within the flat-sheet membrane module. Although, the US degassed the carbonated feed within the module, but no membrane cleaning effect was observed for the US with carbonated feed. Results showed that 37 kHz of US increases the permeation flux higher than 80 kHz, The lowest fouling resistance was obtained for gas bubbling by carbonated feed under 80 kHz, although there was no significant difference between 37 kHz and gas bubbling under 80 kHz. Practical Applications The most important limitation of ultrafiltration is flux decline during processing. Flux decline caused to higher operation cost and decrease the performance of separation. Using the ultrasound (US) treatment at low frequency (37 kHz) and carbonated feed with US at high frequency (80 kHz) can improve the flux permeation significantly. This technique can be applied to ultrafiltration to postpone the fouling and flux decline.

Simulation of the separation of a helium–methane mixture in a flat membrane module

The problem of the membrane separation of a helium–methane mixture containing 0.1 wt % He, which imitates the composition of a helium-rich natural gas field, has been numerically analyzed. The helium and methane flux distribution along the length of a flat-sheet membrane module have been calculated. The distribution of the average mass concentration of helium in the channels is presented. The gas pumping expenditures have been estimated. The optimal working parameters of the gas mixture have been determined. Heating the mixture above 400 K does not enhance the helium–methane separation efficiency.

Comparative study of in-line coagulation and/or ozonization pre-treatment for drinking-water production with spiral-wound ultrafiltration membranes

The application of pre-treatments is a common approach for improving ultrafiltration membrane limitations. However, most studies have been performed for lab-scale hollow-fibre or flat-sheet membrane modules. The present study was conducted to test the performance of fullscale spiral-wound ultrafiltration (UF) membranes for potabilization of influents rich in humic and fulvic acids under different scenarios: (i) direct UF, (ii) with in-line pre-coagulation, (iii) with pre-ozonation, and (iv) with both pre-treatments combined. The membranes were polyvinylidene fluoride with 0.03μm effective pore size. Permeate flow rate was fixed, 1.0m3/h, equivalent to 48 LMH flux. Membrane performance was compared for the aforementioned cases with the following results: feed water pretreatment was required since the effluent quality achieved with direct ultrafiltration was poor and fouling increased. Between pre-ozonation and pre-coagulation, the former was disregarded given the negligible improvement achieved with respect to single ultrafiltration. By contrast, coagulation-flocculation results were remarkably better for both organic matter removal and fouling control. The application of the two pretreatments in series resulted in effluent qualities comparable to those achieved with coagulation-flocculation but fouling rates were much lower and transmembrane pressure growth was minimal, this constituting a promising option for fouling control.

The Effect of Module Geometry on Heat and Mass Transfer in Membrane Distillation

Abstract Some features of Direct Contact Membrane Distillation (DCMD), as one of the interesting membrane processes, has been studied in this effort. 3D computational fluid dynamic simulations were carried out to investigate some geometric parameter effects on flat sheet membrane module performance. It is obvious that using of baffles could noticeably improve the performance of the system. Hence, in present work, some baffle configurations were simulated and some parameters like temperature polarization, vapor flux and pressure drop through module length were investigated. The Simulation was performed based on neglecting viscous flow in membrane pores and dusty gas model was applied to predict vapor flux through membrane. Simulation results predicted that by using the new configuration we could have 40–60% vapor flux improvement (depend on inflow velocity) compared to a module without baffle. It was found that the average temperature polarization (TP), as a proper criteria, was higher for baffled one in all situations.

Study of the rectangular cross-flow flat-sheet membrane module for desalination by vacuum membrane distillation

This work presents a study of the heat and mass transfer performance of desalination in a laboratory-scale rectangular cross-flow flat-sheet membrane module by vacuum membrane distillation (VMD) experiments. Results show that the traditional Nusselt and Sherwood correlations, which are frequently employed in the membrane distillation literature, are not suitably used to estimate the heat and mass transfer coefficients in the VMD system for Reynolds numbers ranging from 150 to 1400. In this study, it was observed that approximately 30% of the experimental data fit well with semi-empirical correlations whose empirical constants are a=2.76×10−3, b=0.97 and c=3.7909. The heat transfer process is limited by the resistances in the feed boundary layer and the membrane. The heat transfer resistance in the membrane increases when that in the feed boundary layer decreases and vice versa. More than 50% of the heat transfer resistances occur in the liquid feed phase at feed flow rates below 1200mL/min, whereas the remaining occur in the membrane itself. At feed flow rates that exceed 1200mL/min, the heat transfer resistance in the membrane becomes dominant. The Knudsen-viscous resistance controls the mass transfer through the membrane while the mass transfer resistance in the liquid feed phase is absent.

Performance Investigation of O-Ring Vacuum Membrane Distillation Module for Water Desalination

A new O-ring flat sheet membrane module design was used to investigate the performance of Vacuum Membrane Distillation (VMD) for water desalination using two commercial polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) flat sheet hydrophobic membranes. The design of the membrane module proved its applicability for achieving a high heat transfer coefficient of the order of 103 (W/m2 K) and a high Reynolds number (Re). VMD experiments were conducted to measure the heat and mass transfer coefficients within the membrane module. The effects of the process parameters, such as the feed temperature, feed flow rate, vacuum degree, and feed concentration, on the permeate flux have been investigated. The feed temperature, feed flow rate, and vacuum degree play an important role in enhancing the performance of the VMD process; therefore, optimizing all of these parameters is the best way to achieve a high permeate flux. The PTFE membrane showed better performance than the PVDF membrane in VMD desalination. The obtained water flux is relatively high compared to that reported in the literature, reaching 43.8 and 52.6 (kg/m2 h) for PVDF and PTFE, respectively. The salt rejection of NaCl was higher than 99% for both membranes.

高性能浸漬型平膜モジュールによるMBRの省エネルギー化

高性能浸漬型平膜モジュールによるMBRの省エネルギー化

Impact of module design on the performance of membrane bioreactors treating municipal wastewater

ABSTRACTMembranes are located in a membrane module that physically seals and isolates the feed stream from the permeate flux in membrane bioreactors (MBRs). Therefore, module type, structure, and geometrical configuration are critical design considerations affecting membrane performance in MBRs. In this study, impact of membrane module design on treatment and filtration performance of MBRs was investigated. For this purpose, two flat sheet membrane modules with different outlet structures and module geometries, including rectangular- and D-shaped, were tested. In addition to the differences in outlet structure and module geometry, size of circular structures which supported membranes in rectangular- and D-shaped modules differed from each other. Considering the results, permeate quality was not affected from the change in the module design. However, the most remarkable impact of the module design was observed on the transmembrane pressure (TMP) evolution and fouling potential. D-shaped membrane module including smaller circular structures resulted in a decrease in fouling potential and thus, this module could be operated longer time in comparison to rectangular-shaped membrane module without a severe TMP increase. The observed differences in TMP increase and fouling potential lead to the hypothesis that module design is a critical factor affecting filtration performance in MBRs.