Flat-sheet Module Research Articles

Efficacious elimination of salts from a convoluted ethylene glycol-water solution employing nanofiltration membranes

ABSTRACT In the current scientific studies, a flat-sheet module pilot plant with an HPP-200 nanofiltration membrane was employed to process an ethylene glycol-water mixture from Jayshree Chemicals, Ankleshwar, India, that contained a significant amount of sodium sulfate. The membrane clogged due to degradation fueled by the excessive salt concentration. Hence, the solution was treated because it was diminished, and the impact of dilution was investigated. Consequently, fouling occurs due to increased flux and reduced concentration polarization. 294, 490, and 784 Kpa pressures were applied to the solution. With the dilution factor, the flow rises while the rejection decreases. Rejection rates range from 97% for membrane plugging without dilution to 92% for five folds and 85% for ten folds dilution. The efficacy of chemical cleaning was investigated using 2% solutions of citric acid and ethylenediamine tetra acetic acid (EDTA). Fourier-transform infrared (FTIR) spectroscopy analysis revealed alterations in membrane structure resulting from interactions with the sodium sulfate feed solution. Scanning Electron microscope (SEM) analysis showed substantial fouling on the membrane surface, which was successfully eliminated through chemical cleaning process. The implementation of dilution and pressure control strategies demonstrated efficacy in the mitigation of fouling phenomena and the enhancement of membrane performance. The efficacy of EDTA in flux recovery (69.84%) was superior to that of citric acid (55.77%) during chemical cleaning processes. These findings have potential to facilitate the implementation of nanofiltration technology in industrial wastewater treatment processes on commercial scale.

Recovery of dissolved methane through a flat sheet module with PDMS, PP, and PVDF membranes

A degassing contactor using a flat sheet membrane module (FM) was operated in sweep gas mode to study the performance of several commercial polymer membranes, both dense (polydimethylsiloxane, PDMS) and microporous (polypropylene, PP, and polyvinylidenefluoride, PVDF), for the recovery of dissolved methane from water. Non-steady state experiments were conducted at different liquid (QL, 3.5–40.5 L h−1) and gas flow rates (QN2, 0.05–15.00 L h−1). In the case of PDMS, PP, and when PVDF was operated at moderate high QL (≥21 L h−1), similar methane removal efficiencies (RE) were obtained. In the case of PVDF operated at relatively low QL (3.5 L h−1), a lower RE was observed. A model for the mass transfer of methane has been selected that is adequate in predicting the experimental results. These results concluded that the mass transfer resistance was mainly located in the liquid phase. Microscopy and especially contact angle measurements were used to monitor the structural and surface stability on the membranes. The membranes were altered during the operation, especially for QL ≥ 21 L h−1, showing a decrease (PDMS and PP) or an increase (PVDF) in hydrophobicity and even cleavages (PDMS). The combination of the FM and contact angle technique has demonstrated to be very versatile and useful for monitoring the variation of the membrane properties during operation.

Showerhead feed distribution for optimized performance of large scale membrane distillation modules

The outstanding capabilities of membrane distillation (MD) process to handle highly saline solutions are still driving research efforts to take this process to the industrial level. MD scale-up remains a challenge as the objective of increasing performance faces several design issues imposed by intrinsic physical constraints. Among the major hurdles encountered with an increase in membrane active area stands temperature polarization, a phenomenon that drastically penalizes MD efficiency. It is shown that in a typical permeate flux distribution over the membrane of an MD module, the highest local permeate flux values contribute to less than 1% of the total module production, while average values add up to half the production, suggesting a dramatic underuse of the membrane active area. Therefore, this investigation explores design opportunities to enhance module performance by reducing polarization for large-scale modules. Using state of the art CFD calculations, it is shown that combined lateral flow and progressive feeding from perforated top wall of the feed channel, and eventually the permeate channel in case of direct contact membrane distillation (DCMD) variant, can considerably increase the productivity of the module. Results further confirm the critical importance of flow distribution at the vicinity of the membrane and its effect on permeate flux. Careful analysis reveals that there is an optimum flow rate ratio between the two feed paths and that the design of the holes of the perforated plate plays a critical role to ensure flow smoothness and reduce temperature polarization. Simulations show that the productivity of a 1 m2 flat sheet module can be enhanced by more than 50% under the same operating conditions, which opens up new opportunities for MD scale up.

CFD simulation of the aeration process and baffle influence in a full-scale commercial flat sheet module

The goal of the present paper is to investigate the aeration process and the enhanced effect of baffles in a full-scale commercial membrane bioreactor (MBR) system configured with a flat sheet (FS) membrane module. Through a computational fluid dynamics (CFD) simulation, two aerated FS membrane modules for full-scale applications with 26 membrane sheets were simulated. The numerical results indicate that the presence of baffles and the distances between the baffle and the outmost membrane sheet have a minor influence on the area-weighted shear stress for full-scale MBRs. In addition, bubble size and the bottom distance between the aerator and membrane bottom do not affect the average shear stress of full-scale FS membrane modules much. However, an increase in air flow rate has a significant effect on the area-weighted shear stress. A large FS membrane module is recommended, as it could achieve the same cleaning effect as the small one with a lower specific aeration demand for membranes.

CFD modeling and simulation of concentration polarization reduction by gas sparging cross-flow nanofiltration

In this study, computational fluid dynamics (CFD) modeling of gas–liquid cross-flow spacer-filled nanofiltration was developed to simulate the process in a vertical flat-sheet module. Experiments were carried out using MgSO4 solution as the feed to validate the developed model. As the novelty of this research, the Eulerian based multiphase method was implemented to assess the effect of air sparging on the concentration polarization and to compute the Sherwood number. It was shown that in most cases air sparging led to a higher permeate flux since it could reduce the concentration polarization layer on the membrane surface up to 73% with the lowest occurring at the air flowrate of 0.4 l min−1. It was also proved that the bubbly flow (0.2, 0.4, and 0.6 l min−1) had no effect on the permeate flux while moving the flow regime to slug flow (0.8 and 1 l min−1) increased the permeate flux. Finally, a good agreement between CFD simulation results and experimental data was seen.

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.

Modelling approach to an ultrafiltration process for the removal of dissolved and colloidal substances from treated wastewater for reuse in recycled paper manufacturing

In this work, ultrafiltration (UF) is used to remove dissolved and colloidal substances (DCS) from a secondary clarifier effluent from a wastewater treatment plant (WWTP) in a papermaking factory. The approach has been to examine and model the decline in permeate flux resulting from membrane fouling. Effluent from a WWTP at a papermaking factory, previously filtered, was used as feed. UF experiments were carried out in a laboratory-scale plant using a 10kDa polyethersulfone (PES) UF membrane in a flat sheet module with an active area of 154.8cm2. The transmembrane pressure (TMP) (1–3bar) and crossflow rate (1.5–4.5L/min) were varied during the experiments, at constant temperature (22±0.5°C). Experimental results from UF tests were expressed in terms of permeate flux (Jp) as a function of time to check modified Hermia’s models adapted to crossflow filtration. The parameters of these models were theoretically estimated. The predicted results were compared with experimental data with a high goodness of fit. The results showed that the phenomenon controlling fouling, under most of the conditions tested, was intermediate blocking (R2>0.96). Measurements of particle size distribution and zeta potential near the isoelectric point, showed a substantial reduction in colloidal compounds. Additionally, given that COD was removed down to 110mg/L, it could be said that UF is suitable for producing water that can be reused in different papermaking processes.

Slug and bubble flows in a flat sheet ultrafiltration module: Experiments and numerical simulation

In this paper, the effect of gas bubbling including slug and bubble flows on enhancing shear force in an ultrafiltration (UF) process in a flat sheet module is investigated experimentally by image processing and numerically using the OpenFOAM software. In order to study characteristics of bubbles in the slug and bubble flows, the flat sheet module is analyzed by a video system facilitated with a high speed camera. The experimental results show that the average diameter of the slug flow is much larger than that of the bubble flow. The permeate flux for the slug and bubble flows is increased by 78% and 30%, respectively, compared to the case with no gas bubbling. The numerical results are shown to be in good agreement with those of the measurements both qualitatively and quantitatively. The results of simulations also demonstrate that although both flow patterns increase the shear stress by increasing the velocity gradient and/or vorticity, the shear stress induced by the slug flow is considerably larger. Therefore, the slug flow with a higher induced shear stress is more effective on the enhancement of the permeate flux in a UF process.

Direct observation of flow and bubble behavior in flat sheet modules with a distributor

The air sparging method was widely used in membrane modules to enhance performance of separation. In this article, bubble behavior in tubular and flat sheet flow module with different air sparging devices was investigated.

Quantitative estimation of internal concentration polarization in a spiral wound forward osmosis membrane module compared to a flat sheet membrane module

Internal concentration polarization (ICP) within the forward osmosis (FO) membrane affects the reduction of driving force. The magnitude of ICP in the FO membrane was investigated experimentally by measuring water flux in both spiral wound (SW) and flat-sheet (FS) modules with different draw solutions (sodium chloride, sodium sulfate, and disodium phosphate). The FO SW module always shows inferior water flux performance to the FO FS module. The water flux in the FO SW module can be easily estimated by just changing structure parameter. The estimated structure parameter in the FO SW module is 9.1325×10−4 m, which is quite higher than 4.2×10−4 m in the FO FS module. The increase of the structure parameter is attributed to the bending of the FO membrane in the SW module. It can be concluded that a module design such like SW type is not suitable for the FO process.

Heavy metals removal by osmotic membrane bioreactor (OMBR) and their effect on sludge properties

Osmotic membrane bioreactor (OMBR) was operated to treat high strength wastewater. Cellulose triacetate (CTA) membrane, having effective membrane area of 0.12m2, in a flat-sheet module configuration was submerged in a bio-tank (working volume 4.5L). SRT of 20days and periodic removal of supernatant from settled sludge were maintained to control the salinity level in the bio-tank. Keeping operating conditions constant, the OMBR system was operated in treating 2, 5 and 10mg/L of Chromium (Cr) and Lead (Pb) metals, respectively of the high strength wastewater. Effect of these metals on membrane fouling, sludge characteristics and treatment performances in term of organic carbon, ammonium-nitrogen and phosphate-phosphorous were investigated. Biomass properties including specific oxygen uptake rate (SOUR), MLSS concentration and capillary suction time (CST) were determined. There was no significant effect of lower concentrations of Cr on sludge properties while 63% of biomass reduction and 42% of biomass activity (SOUR) inhibition were reported for 10mg/L of Cr. In case of Pb, even its lower concentrations of 2 and 5mg/L were producing toxic effects on sludge properties i.e., 14.7 and 40% of biomass (MLSS) and 72 and 83% of bioactivity (SOUR) inhibitions were observed for the Pb concentrations, respectively.

Study of NaCl permeability through a non-porous polypropylene film

The possibility of NaCl permeation through a polymeric matrix of polypropylene membranes was studied. A non-porous polypropylene film, which was assembled in a flat sheet module, separates a saturated solution of NaCl from pure water. The changes of water composition were determined by the application of ion chromatography and measurements of the electric conductivity. The studies were carried out for 4 years, and the permeation of salt through the polypropylene film from the feed to pure water was not observed over this period. In the first month the results of studies were affected by the impurities, which were introduced to pure water from the installation walls. Moreover, the electrical conductivity of water was also enhanced by adsorption of components from the ambient air. The used polypropylene film demonstrated a high resistance to polymer degradation. SEM observations revealed that the film was free from micropores and cracks after 4 years of studies. The DSC examinations demonstrated only slight changes in the polymer crystallinity. FTIR spectra recorded for a new film and film assembled in the module were similar. The XPS studies did not demonstrated the presence of NaCl in the surface layer of polymer on the side of brine flow. Moreover, a significant change of material hydrophobocity did not take place over the period studied. A dynamic wetting angle measured for a new film amounted to 103–106° and was decreased to 95° on the water side and to 84° on the brine side after 4 years of contact of the polymer with water and a saturated NaCl solution, respectively.

Addition of Particles for Fouling Minimization in Membrane Bioreactors – Permeability Performance, Fluid Dynamics, and Rheology

AbstractMembrane bioreactors (MBR) with submerged flat sheet modules follow the airlift loop flow principle. The addition of particles is a new development in MBR fouling control. Experiments with plastic beads clearly show a mechanical cleaning effect. Biologically active beads (quorum quenching) can further reduce membrane fouling. The effectiveness of the particles depends on the flow conditions, though. To select or design such additives properly, as well as to optimize air flow rates, the complex fluid dynamics of the multiphase airlift loop flow and the rheology of the biomass need to be understood.

Performance of nanofiltration and reverse osmosis membranes for arsenic removal from drinking water

The removal of arsenic was investigated by four types of thin-film polyamide nanofiltration (NF) (NF270, NF90) and reverse osmosis (RO) (XLE, BW30) membranes in a flat-sheet module. The influence of membrane types, pressure, pH, and pre-oxidation step on the removal of arsenic (As(III)) was investigated. Initial As(III) concentration was 100 μg/l for all of the experiments. Flux was determined over a pressure range of 3.5–10 bar for both NF and RO membranes. Experiments were conducted at pH 3.5, 5, 7.5, and 10 to evaluate the effect of pH on As(III) removal. The impact of pre-oxidation and oxidant concentrations on As(III) removal were also evaluated. It was found that the percentage of As(III) removal of RO membranes were in the range of 97–99 for all transmembrane pressure applied. In the range of operating conditions, As(III) and As(V) rejection were found almost equally good by RO membranes. RO permeate met the WHO and Turkish standard for arsenic. Pre-oxidation step improved the rejection performance of NF. Nevertheless, NF permeate did not meet the standards in the range of operating conditions.

Evaluation of cleaning efficiency of ultrafiltration membranes fouled by BSA using FTIR–ATR as a tool

The goal of this paper was to study the cleaning of two polyethersulfone (PES) membranes of different molecular weight and fouled with BSA solution. Ultrafiltration (UF) membranes were tested in a flat sheet module. Fouling experiments were carried out at a transmembrane pressure of 2bar and cross flow velocity of 2m/s during 2h. Cleaning experiments were performed at 1bar and 2.2m/s. To compare the efficiency of different cleaning solutions (NaOH and P3-Ultrasil 115), quantification of residual proteins on the membrane was carried out by FTIR–ATR. To have a better understanding of the cleaning process, characteristics of the feed solution and of the membranes were considered and contact angle of the membranes before and after the cleaning was measured. Membrane resistances were also calculated at the different stages. Results from resistances showed that reversible fouling prevail over irreversible fouling for both membranes. P3-Ultrasil 115 was a better cleaning agent than NaOH solution since cleaning efficiencies (CE) of 100% for both membranes were achieved for P3-Ultrasil 115 solution. Residual proteins on the membrane after the cleaning were measured both by FTIR–ATR and Pierce-BCA method. Results showed that 100% of permeability recovery did not imply the complete BSA removal from the membrane. However, these measurements corroborated that P3-Ultrasil 115 had removed a higher amount of proteins than NaOH solution.

Purifying fluoride-contaminated water by a novel forward osmosis design with enhanced flux under reduced concentration polarization

For purifying fluoride-contaminated water, a new forward osmosis scheme in horizontal flat-sheet cross flow module was designed and investigated. Effects of pressure, cross flow rate, draw solution and alignment of membrane module on separation and flux were studied. Concentration polarization and reverse salt diffusion got significantly reduced in the new hydrodynamic regime. This resulted in less membrane fouling, better solute separation and higher pure water flux than in a conventional module. The entire scheme was completed in two stages-an upstream forward osmosis for separating pure water from contaminated water and a downstream nanofiltration operation for continuous recovery and recycle of draw solute. Synchronization of these two stages of operation resulted in a continuous, steady-state process. From a set of commercial membranes, two polyamide composite membranes were screened out for the upstream and downstream filtrations. A 0.3-M NaCl solution was found to be the best one for forward osmosis draw solution. Potable water with less than 1% residual fluoride could be produced at a high flux of 60-62 L m(-2) h(-1) whereas more than 99% draw solute could be recovered and recycled in the downstream nanofiltration stage from where flux was 62-65 L m(-2) h(-1).

Modeling full-scale osmotic membrane bioreactor systems with high sludge retention and low salt concentration factor for wastewater reclamation

A full-scale model was developed to find optimal design parameters for osmotic membrane bioreactor (OMBR) and reverse osmosis (RO) hybrid system for wastewater reclamation. The model simulates salt accumulation, draw solution dilution and water flux in OMBR with sludge concentrator for high retention and low salt concentration factor. The full-scale OMBR simulation results reveal that flat-sheet module with spacers exhibits slightly higher flux than hollow-fiber; forward osmosis (FO) membrane with high water permeability, low salt permeability, and low resistance to salt diffusion shows high water flux; an optimal water recovery around 50% ensures high flux and no adverse effect on microbial activity; and FO membrane cost decreases and RO energy consumption and product water concentration increases at higher DS flow rates and concentrations. The simulated FO water flux and RO energy consumption ranges from 3.03 to 13.76LMH and 0.35 to 1.39kWh/m3, respectively.

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.

Separation of soybean oil from liquefied n‐butane and liquefied petroleum gas by membrane separation process

This work investigates the separation of soybean oil/compressed n‐butane and soybean oil/liquefied petroleum gas (LPG) mixtures, using ultra‐ and nanofiltration membranes. For this purpose, soybean oil/n‐butane and soybean oil/LPG in the mass ratio of 1:3 were continuously fed into a flat sheet module without the recycle. The effects of the feed pressure (10, 20, and 30 bar), the pressure difference (1, 5, and 10 bar) and the pre‐treatment with ethanol and n‐propanol on the oil permeate flux and oil retention were investigated. The membranes with best performance (higher oil retention combined with high solvent permeate flux) were Sepa GM (4 kDa) and Sepa HL (98 % MgSO4), previously conditioned in ethanol. The Sepa GM membrane showed oil retention between 95 to 99 %. The Sepa HL membrane showed oil retention between 83 to 97 %. The pre‐treatment with ethanol improved the permeate flux. In most of the experimental conditions severe membrane fouling was observed. A change in the permeate flux and oil retention behaviour was observed in the assays with LPG as solvent due to the different gas composition when compared with n‐butane.

Modeling of permeate flux and mass transfer resistances in the reclamation of molasses wastewater by a novel gas-sparged nanofiltration

A semi-empirical model has been applied to predict the permeate flux and mass transfer resistances during the cross flow nanofiltration of molasses wastewater in flat-sheet module. The model includes laminar flow regime as well as flow in presence of gas sparging at two different gas velocities. Membrane hydraulic resistance (Rm), osmotic pressure resistance (Rosm) and the concentration polarization resistance (Rcp) were considered in series. The concentration polarization resistance was correlated to the operating conditions, namely, the feed concentration, the trans-membrane pressure difference and the cross flow velocity for a selected range of experiments. There was an appreciable reduction of concentration polarization resistance Rcpspar in presence of gas sparging. Both the concentration polarization resistance Rcplam and osmotic pressure resistance Rosm decreased with cross-flow velocity, but increased with feed concentration and the operating pressure. Experimental and theoretical permeate flux values as a function of cross flow velocity for both the cases, in the presence and absence of gas sparging, were also compared.