Flat Sheet Membrane Module Research Articles

Fluoride in groundwater: low-cost separation and stabilization by response surface optimization

A nanomembrane-based hybrid treatment system for separation of fluoride from contaminated groundwater and its subsequent stabilization in a solid matrix through chemical coagulation–precipitation process using response surface optimization for safe disposal were designed and investigated. The continuous flat-sheet cross-flow nanofiltration membrane module with well-screened commercial polyamide composite membrane succeeded in removing 99 % fluoride from water while yielding a pure water flux as high as 158–160 L/m2h of a transmembrane hydraulic pressure of only 14 bars. Such an operating pressure is much lower than that required in reverse osmosis for the same separation. The designed system for the first time provides a total solution to a complex problem in a very simple, compact, flexible, and novel design that ensures continuous, steady, and hassle-free long-term operation without the necessity for frequent replacement of membranes. The approximate cost for production of 1000 L of safe drinking water from fluoride-contaminated groundwater computes to only $ 1.4, indicating affordability in adopting the low-cost, high-flux water purification system by the affected people in many parts of the world.

A new folded plate membrane module for hydrodynamic characteristics improvement and flux enhancement

Abstract To intensify the air scouring efficiency and reduce the membrane fouling, a new folded plate membrane module (FPMM) was designed by modifying the configuration of conventional flat sheet membrane module (FSMM). The hydrodynamic characteristics near the folded plate membrane surface, and its filtration performance in different operating conditions were studied. The particle image velocimetry (PIV) measurement results showed that, the higher flow velocity, the stronger turbulence, and more vortices existed near the folded plate membrane surface. The stable flux of the FPMMs had an increase of 17.8–57.7% over that of the FSMM, and the optimal vertical inclination angle was 15°. Moreover, in the filtration process, the flux enhancement of the FPMM was affected by the aeration intensity, yeast suspension concentration and trans-membrane pressure (TMP).

Vacuum enhanced direct contact membrane distillation for oil field produced water desalination: specific energy consumption and energy efficiency

This paper presents a study for energy requirements of lab-scale membrane distillation (MD) unit. This lab unit consists of flat-sheet membrane module with two circulation pumps, heater, and cooler to study the effect of different operating conditions on both specific energy consumption (SEC) and energy efficiency (ηE) via vacuum enhanced direct contact MD method. The flux and the two parameters of energy (SEC, ηE) were measured using different temperatures, different feed flow rates, and different feed salt concentrations. The two membranes used were neat polypropylene (PP) membrane and PP/multi-walled carbon nanotubes (MWCNTs) composite membrane. The membranes were synthesized via phase inversion process, using xylene as a solvent, methyl iso-butyl ketone as a coagulant and dispersion medium for MWCNTs. The results showed that the highest ηE was 39.5 with SEC 1,649.2 kW h/m3 at flux 52.5 kg/m2 h using 15 L/min feed flow rate of synthetic feed water with salt concentration 10,000 ppm at 55°C feed temperature. On the other hand, using our prepared membrane for the desalination of oil field water, the values of ηE and SEC were 12.1 and 4,189.5 kW h/m3, respectively.

Effect of single and blended amine carriers on CO2 separation from CO2/N2 mixtures using crosslinked thin-film poly(vinyl alcohol) composite membrane

This article reports effect of different single and blended amine carriers on binary gas (20% CO2 balance N2) separation using novel CO2-selective crosslinked thin-film poly(vinyl alcohol) composite membranes. The characterization of the thin-film active layer had been carried out by Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The transport properties of CO2 (CO2 and N2 fluxes, CO2 and N2 permeability, and CO2/N2 selectivity) across the membrane were examined using counter flow flat sheet membrane module. The effects of active layer thickness (41 to 84micron), feed absolute pressure (1.7 to 6.2atm), temperature (90 to 125°C), and sweep side water flow rate (0.02 to 0.075cm3/min) on transport properties of CO2 across the membrane were analyzed. The dense layer containing amine carrier displays both high selectivity and permeability. It has been seen that the composite membrane of 25wt% poly(allylamine) and 15wt% 2-amino-2-hydroxymethyl-1,3-propanediol with 44 micron active layer thickness is having maximum CO2/N2 selectivity of 434 and CO2 permeability of 1826 Barrer at 2.8atm feed side absolute pressure and 100°C temperature.

Mathematical modelling and numerical simulation of CO2/CH4 separation in a polymeric membrane

CO2 capture from natural gas was experimentally and theoretically studied using a dead-end polymeric permeation cell. A numerical model was proposed for the separation of CO2/CH4 using Polytetrafluoroethylene (PTFE) in a flat sheet membrane module and developed based upon the continuity, momentum and mass transfer equations. The slip velocity condition was considered to show the reflection of gas flow in contact with the membrane surface. The solution method was based on the well-known SIMPLE algorithm and implemented using MATLAB to determine the velocity and concentration profiles. Due to change in velocity direction in the membrane module, the hybrid differencing scheme was used to solve the diffusion–convection equation. The results of the model were compared with the experimental data obtained as part of this work and good agreement was observed. The distribution of CO2 concentration inside the feed and permeate chambers was shown and the velocity profile at the membrane surface was also determined using reflection factor for polymeric membrane. The modelling result revealed that increasing the amount of CO2 in gas feed resulted in an increase in the CO2 in the permeate stream while the gas feed pressure increased. By changing the permeability, the model developed by use of the solution–diffusion concept could be used for all polymeric membranes with flat sheet modules.

Thin film composite hollow fibre forward osmosis membrane module for the desalination of brackish groundwater for fertigation

The performance of recently developed polyamide thin film composite hollow fibre forward osmosis (HFFO) membrane module was assessed for the desalination of brackish groundwater for fertigation. Four different fertilisers were used as draw solution (DS) with real BGW from the Murray–Darling Basin in Australia. Membrane charge and its electrostatic interactions with ions played a significant role in the performance of the HFFO module using fertiliser as DS. Negatively charged polyamide layer promotes sorption of multivalent cations such as Ca2+ enhancing ion flux and membrane scaling. Inorganic scaling occurred both on active layer and inside the support layer depending on the types of fertiliser DS used resulting in severe flux decline and this study therefore underscores the importance of selecting suitable fertilisers for the fertiliser drawn forward osmosis (FDFO) process. Water flux under active layer DS membrane orientation was about twice as high as the other orientation indicating the need to further optimise the membrane support structure formation. Water flux slightly improved at higher crossflow rates due to enhanced mass transfer on the fibre lumen side. At 45% packing density, HFFO could have three times more membrane area and four times more volumetric flux output for an equivalent 8040 cellulose triacetate flat-sheet FO membrane module.

The application of saw-tooth promoter for flat sheet membrane filtration

A novel saw-tooth turbulence promoter was developed to improve the filtration performance of flat sheet membrane module (FSMM). The flux improvement mechanism was investigated through flow field test by particle image velocimetry (PIV). Results showed that the vortex produced by saw-tooth promoter intensified the mixing of fluid, which was favorable for the back transport of particles. Membrane shear rates in saw-tooth membrane modules (STMMs) were above 1.98 times higher than that in normal flat sheet membrane module. Particle deposition on membrane surface was effectively retarded. Flux improvement was verified by microfiltration of SiC suspension. Results showed that compared to the normal filtration method, saw-tooth promoter can improve the flux by 115.7%–258.0%, with a reduction of specific energy consumption above 33.8%. It was demonstrated that the saw-tooth promoter can improve filtration performance of flat sheet membrane module through flow field intensification.

Fluid dynamics of bubble swarms rising in Newtonian and non-Newtonian liquids in flat sheet membrane systems

The bubble swarm behavior in a system comparable to a flat sheet membrane module was investigated. The parameters channel depth, superficial gas velocity, superimposed liquid velocity and viscosity of the continuous phase were varied. Besides water as continuous phase, a non-Newtonian liquid was used with respect to the rheology of real waste water sludge. The gas hold-up was determined for 144 parameter combinations with high speed imaging and the shear stress – important for the fouling mitigation – was determined for 72 parameter combinations with the electrodiffusion method. To the authors׳ knowledge, this is the first application of the electrodiffusion method in a bubbly flow with a non-Newtonian liquid. For the two properties gas hold-up and the shear stress describing correlations were found taking all parameters into account. In both cases, the strongest influences were found for the gas velocity and the rheology of the continuous phase. Regarding the shear stresses, the median values were up to 3.2Pa while the maximum values were up to 9.1Pa. Depending on the parameter combination, a significant influence of the rheology was found disagreeing with the statement of the transferability of the results gained in water to real waste water systems mentioned in some papers.

Theoretical modeling of direct contact membrane distillation (DCMD): effects of operation parameters on flux

In this research, a mathematical model for calculating and predicting flux through direct contact membrane distillation in flat-sheet membrane modules was presented. The membrane properties’ and permeate and feed streams’ main specifications were considered as model input parameters. The effects of simultaneous heat and mass transfer were investigated. The developed mathematical model was written in Visual Basic language based on heat and mass balances. The influences of process parameters such as temperature, flow rate, feed concentration, and membrane properties (pore size) on flux and temperature polarization coefficient were evaluated by the model. The modeling results were compared with some experimental data and good agreement was observed.

Computational fluid dynamics modeling and experimental studies of oil-in-water emulsion microfiltration in a flat sheet membrane using Eulerian approach

In the present study, microfiltration of oil-in-water emulsion was experimentally and numerically studied in a flat sheet membrane module. Due to the significance of fluid flow hydrodynamics on the concentration polarization phenomenon and membrane performance, 2D computational fluid dynamics modeling was conducted to simulate oil concentration profile in the mass boundary layer and to predict permeate flux. Multi-phase flow equations, based on an Eulerian multiphase model, for continuous and dispersed phase were solved using Navier–Stokes equations coupled with Darcy׳s law for the porous media. This novel approach considered the interparticle interactions of oil droplets which led to much more accurate results in comparison with other previous works. Besides, the capabilities of this new model in predicting oil concentration profile and mass boundary layer behavior were checked in different operating conditions, in which the predicted data showed good accordance to the experimental results and CP theory.

Rising behaviour of single bubbles in narrow rectangular channels in Newtonian and non-Newtonian liquids

A phenomenological investigation of single bubbles ascending in a confined geometry with a rectangular cross section was done. Motivated by the goal to get a deeper understanding of the bubble behaviour in flat sheet membrane modules used in membrane bioreactors, the parameters channel depth (=spacing, 5–7mm), bubble size (3–9mm), superimposed liquid velocity (0–23.5cm/s) and rheology of the continuous phase (Newtonian, shear-thinning) were varied. The shear-thinning liquid was used to simulate the rheological behaviour of activated sludge apparent in membrane bioreactors. The analysed properties included the rising paths, bubble shape, absolute and relative terminal rise velocities, friction factors and oscillation frequencies and amplitudes of the bubble.As expected, a significant influence of the rheology of the continuous phase was found on the rising behaviour. In the shear-thinning liquid, the bubbles followed mostly a straight rising path with negligible oscillations. The variation of the channel depth mainly had an influence on the terminal rise velocity of the bubbles ascending in the shear-thinning liquid with higher values in the channel with the larger channel depth. Increasing the bubble size led to higher rising velocities and to enhanced oscillations.

Influence of surface hydrophilicity on polytetrafluoroethylene flat sheet membrane fouling in a submerged membrane bioreactor using two activated sludges with different characteristics

This study focused on how membrane surface hydrophilicity affects fouling in a membrane bioreactor. A lab-scale membrane bioreactor incorporating immersed polytetrafluoroethylene flat-sheet membrane modules with different contact angles (approximately 70° and 130°) was operated using the inocula activated sludge taken from a lab reactor and from a municipal wastewater treatment plant (WWTP). The reactor also contained a polyvinylidene difluoride flat-sheet membrane module as a reference. The hydrophobicity of the WWTP sludge was higher than that of the lab-reactor sludge. Results showed that when lab-reactor sludge was used, increases in transmembrane pressure (TMP) for the hydrophobic membrane with a high contact angle occurred more rapidly than for the hydrophilic membrane with a low contact angle. In contrast, when the WWTP sludge was used, TMP increases for the hydrophilic membrane occurred more rapidly than for the hydrophobic membrane. These results indicate that the effects of surface hydrophilicity on membrane fouling depend on the hydrophobicity of the activated sludge. When the WWTP sludge was used, the hydrophobic membrane exhibited much higher cake layer resistance than did the hydrophilic membrane. Formation of a dense cake layer on hydrophobic polytetrafluoroethylene membranes may deter adhesion of foulants on membrane surfaces.

Heat transfer in the rectangular cross-flow flat-sheet membrane module for vacuum membrane distillation

This paper presents a study of heat transfer coefficients of boundary layers in a laboratory-scale rectangular cross-flow flat-sheet membrane module by using distilled water vacuum membrane distillation (VMD) experiments. Results show that the traditional heat transfer correlations, which are mostly employed in the membrane distillation literature, are not suitably used to predict the heat transfer process in the VMD system for the Reynolds numbers ranging from 300 to 1090. This study formulates a new semi-empirical heat transfer correlation by suggesting Knudsen-viscous mechanism governs the water vapour across the membrane. Compared to the feed flow rate, the feed temperature is the limit to the heat transfer. The heat transfer coefficients are strongly dependent on the physical properties of the feed solution, but less relied on the design of the membrane module.

Studies on simulation and experiments of ethanol–water mixture separation by VMD using a PTFE flat membrane module

Model parameters modification and numerical simulation based on the Knudsen–viscous transition model to predict the vacuum membrane distillation (VMD) performance of ethanol–water mixture and experiments were studied in a polytetrafluoroethylene flat-sheet membrane module. A novel approach to determine the model parameters K and B (modified Knudsen diffusion and viscous flow membrane characteristics, respectively) consisted of membrane morphological parameters was especially developed by fitting the water VMD experimental results. Furthermore, linear relations between the modified model parameter K or B and feed temperature were first established, and then successfully employed to predict by simulation the separation performances of 5wt% ethanol–water mixture. The experiments of ethanol–water VMD demonstrated that the fluxes of ethanol and water both increased with temperature or vacuum degree, but the separation factor decreased. The simulation values agree quite well with experimental ones, finding the minimum and maximum discrepancies are 0.5% and 9.6% for flux and separation factor, respectively.

Fluid Dynamic Optimization of Flat Sheet Membrane Modules – Movement of Bubbles in Vertical Channels

Fouling is one of the key challenges in the operation of membrane bioreactors. Aeration is a simple but cost-intensive measure to clean the membranes. The aim of this project is to deepen the understanding of the behavior of the bubbles in such geometries to be able to optimize the cleaning of membrane systems and make them more cost-effective. Therefore, with respect to flat sheet membrane modules, the rise of a single bubble in a rectangular channel was investigated experimentally and numerically. The experimental part was performed with a high speed camera and the images were analyzed with the help of NI LabView, Vision Development Module and MS Excel. The software was used to determine the centre of mass of the bubble on each image which provides the rising path when combined. This rising path is determined for different parameter combinations varied bubble sizes and superimposed liquid velocities. The same parameter combinations were investigated numerically with the help of Ansys Fluent. Based on the rising paths, a comparison of the simulation and experiments is possible. Specifically the terminal rise velocity, the oscillation frequency and the amplitude are used for comparison.

Theoretical and Experimental Investigations of Flat Sheet Membrane Module Types for High Capacity Gas Separation Applications

AbstractGas permeation is increasingly considered for high capacity applications. This contribution discusses the commonly employed membrane module types for flat sheet membranes and suggests a new module concept. The applications considered are the separation of CO2 from flue gas and hydrocarbon dewpointing of natural gas. Rigorous models for predicting the operating performance of the module types are described. Pilot plant experiments were conducted to validate the model for envelope type modules. Simulation studies were carried out to predict the performances of the different module types for the two examples and assess their advantages and disadvantages.

Alleviation of flux decline in cross flow nanofiltration of two-component dye and salt mixture by low frequency ultrasonic irradiation

Gradual reduction of steady state permeate flux (throughput) over a period of time often mars the performance of nanofiltration process. In the present study, nanofiltration of two-component dye and NaCl mixture containing Reactive Black 5 and C.I Reactive yellow 160 was carried out in a flat sheet membrane module with hydrophilized polyamide membrane (molecular weight cut off 400) over a range of operating conditions. Results indicate that the flux decline with time could be significantly mitigated under low frequency (34±3kHz) ultrasonic irradiation when compared with the conventional unassisted nanofiltration. Various filtration resistances were determined using a simple resistance-in-series model, which revealed that concentration polarization resistance could be effectively decreased by ultrasonic irradiation. Effect of several parameters such as mode of irradiation (viz. continuous and intermittent), trans-membrane pressure and temperature were studied and discussed with respect to existing theories. The power consumption of the high pressure plunger pump at different feed pressures and the ultrasonic power transferred to the water bath at three different temperatures were estimated. More than 96% of color, and 65% TDS were removed from the treated water accompanied by a marked reduction of COD. The process allowed the production of permeate stream with great reutilization possibilities.

Comprehensive simulation of flat-sheet membrane element performance in steady state desalination

This study is a step towards the development of a comprehensive computational tool, simulating in detail the performance of Spiral Wound Membrane modules, presently unavailable. The development of a detailed two-dimensional model is reported herein, for flat-sheet membrane modules, by incorporating small length-scale CFD results at the retentate side and accounting for permeate compartment variables. By considering the interacting (through the semi-permeable membrane) flow fields at these two compartments, the model simulates the steady-state desalination under constant space-averaged permeate recovery. Aided by analysis of the mechanisms involved and by appropriate non-dimensionalization of the governing equations, efficient numerical techniques are adapted, leading to the development of a general purpose computational tool. The distribution of all key process parameters (at both flow compartments, throughout the membrane envelop) can be predicted, as a function of the membrane sheet and the spacers geometrical characteristics; thus the new simulator is most appropriate for module design optimization, parametric studies and other applications. The new algorithm is very efficient from the computational point of view. The features and capabilities of this advanced simulator are demonstrated by presenting several detailed results of operating parameters, focusing on the two-dimensional aspects of the problem.

Bubble induced shear stress in flat sheet membrane systems—Serial examination of single bubble experiments with the electrodiffusion method

With regard to the improvement of the cleaning process of flat sheet membrane modules by aeration, a statistical analysis of the shear stress generated by single bubbles is shown for 21 different parameter combinations of varied channel depths, bubble sizes and liquid velocities. A fully automated rig allowed the generation of a sufficient database of shear stress data gained with the electrodiffusion method (EDM). The maximum shear stresses and the global shear stress levels, where the latter represents the global shear stress fluctuations, were determined. To the authors' knowledge, for the first time in membrane research a transient correction of the EDM data was performed which is necessary in cases of highly transient processes. By showing different probability ranges gained from cumulative distribution functions in bar plots, a way of presenting the data was introduced that simplifies the comparison between the different geometrical and operating parameter combinations. Additionally, this type of diagram offers a very comprehensive overview of the measured data. Both the maximum shear stress and the global shear stress levels are larger when the bubble is larger than the channel depth and when an additional liquid velocity is superimposed. In all cases, the transient correction yielded higher values. Thus it is necessary to take this measure.In the investigated range, the highest maximum values were obtained for the case with superimposed liquid velocity, a channel depth of 5mm and a bubble size of 9mm with appr. 1.3Pa (steady analysis) or 4.7Pa (transient corrected analysis), respectively. The largest fluctuation ranges of the global shear stress levels were obtained for a channel depth of 5mm and a bubble size of 9mm with values from appr. 0.2 to 1.1Pa (steady analysis) or 0 to 2.6Pa (transient corrected analysis).

Biomass Leachate Treatment and Nutrient Recovery Using Reverse Osmosis: Experimental Study and Hybrid Artificial Neural Network Modeling

The application of reverse osmosis (RO) to recover nutrients from biomass leachate, with special reference to permeate flux behavior during the filtration of the leachate, is investigated in this paper through a comprehensive laboratory and modeling approach. Various sources of biomass, including soybean straw, switchgrass, and miscanthus, were industrially leached using distilled water with agitation during the extraction experiments. The leachates were filtered using a RO flat sheet membrane module to recover the nutrients and water. On the basis of inductively coupled plasma (ICP) analytical results, calcium, magnesium, phosphorus, and silica for all types of biomass leachate samples had rejection efficiencies of >80%. Permeate flux decreased sharply at the beginning of the filtration, followed by a slight decline during the filtration process. A hybrid intelligent model based on a feed-forward artificial neural network (ANN) was also developed to estimate the permeate flux during the filtration in terms of the filtration time and total solid concentration in the leachate. A Levenberg–Marquardt optimization algorithm was chosen to perform the training phase for the network. An ANN with four neurons in one hidden layer was selected as the optimum structure, such that a maximum percent absolute error of 14% was attained while predicting the permeate flux. A reasonable agreement was observed between the ANN predictions and experimental data, which exhibits the potential usefulness of the hybrid ANN model to predict permeate flux during RO filtration of biomass leachate.