Flat Sheet Membranes Research Articles

Effect of Antiscalant Usage and Air Diffuser Perforation Diameter on Filtration Performance of Submerged Flat Sheet MBR for Treatment of High Salinity and Scaling Propensity Wastewater

Membrane fouling and mineral scaling remain major drawbacks for MBR technology. Membrane fouling reduces the filtration ability in MBR systems by increasing transmembrane pressure (TMP) and thus increases the operational cost. This study focused on the application of commercially available antiscalant in a pilot MBR system and the effect of diffuser perforation diameter for the treatment of high mineral scaling propensity wastewater. Submerged flat sheet membranes (Kubota, nominal pore size: 0.4 µm) were used in the pilot-scale test unit operated in the wastewater treatment plant of ITOB Organized Industrial Zone, Izmir, Turkey. The commercially available antiscalants employed were coded AS-1 and AS-2 for antiscalant study. Long term effect of the two antiscalants employed was investigated under high mixed liquor suspended solid (MLSS) concentration (17–21 g/L) for two months of MBR operation. The effect of low MLSS concentration (10–13 g/L) was also studied without changing the concentration of antiscalant type and concentration. AS-1 was found to be more effective in terms of mineral scale control. The effect of diffuser perforation diameter (1, 3 and 5 mm) on mineral scaling minimization in MBR pilot system was also studied. The best performance with respect to membrane fouling control was found with an air diffuser having 3 mm of diffuser perforated diameter. Some quality analyses of the product water were also carried out to assess the effect of antiscalant addition on microbial activities in the MBR unit. The findings in this study reveal that the use of antiscalants has not affected biological treatment performance of MBR pilot system. The removal ranges obtained during all MBR studies were 98.47–99.9%, 84.62–99.4%, 89.5–98.5%, 86.90–99.9%, 67.01–99.2%, 75.03–93.9%, and 20.36–71.5% for total suspended solid (TSS), color, chemical oxygen demand (COD), NH4-N, PO4-P, NO2-N, and total nitrogen (TN) respectively.

Nanoparticle-Enhanced PVDF Flat-Sheet Membranes for Seawater Desalination in Direct Contact Membrane Distillation

In this study, hydrophobic functionalized carbon nanotubes (fCNTs) and silica nanoparticles (fSiO2NPs) were incorporated into polyvinylidene fluoride (PVDF) flat-sheet membranes to improve their performance in membrane distillation (MD). The performance of the as-synthesized membranes was evaluated against commercial reference polytetrafluoroethylene (PTFE) flat-sheet membranes. The water contact angle (WCA) and liquid entry pressure (LEP) of the PVDF membrane were compromised after incorporation of hydrophilic pore forming polyvinylpyrrolidone (PVP). These parameters were key in ensuring high salt rejections in MD processes. Upon incorporation of fCNTS and fSiO2NPs, WCA and LEP improved to 103.61° and 590 kPa, respectively. Moreover, the NP additives enhanced membrane surface roughness. Thus, an increase in membrane roughness improved WCA and resistance to membrane wetting. High salt rejection (>99%) and stable fluxes (39.77 kg m-2 h-1) were recorded throughout a 3 h process evaluation where 3.5 wt% NaCl solution was used as feed. These findings were recorded at feed temperature of 60 ℃. Evidently, this study substantiated the necessity of high feed temperatures towards high rates of water recovery.

Efficient Recovery of Organic Matter from Municipal Wastewater by a High-Rate Membrane Bioreactor Equipped with Flat-Sheet Ceramic Membranes

High-rate processes have been investigated for the recovery of organic matter from municipal wastewater. High-rate membrane bioreactors (HR-MBRs) may simultaneously achieve the increased recovery of carbon and high effluent quality, although control of membrane fouling is extremely difficult. To address the severe fouling in HR-MBRs, the combination of granular scouring and frequent chemically enhanced backwashing was examined. The use of robust flat-sheet ceramic membranes enabled the application of those cleaning strategies. Experiments were carried out at an existing wastewater treatment plant. To operate as a high-rate system, the bioreactor solid residence time and hydraulic residence time were set at 0.5 days and 1.6 h, respectively. Although a relatively high flux of 20 L m-2 h-1 was applied, the proposed HR-MBR exhibited a very low fouling rate of 1.3 kPa/day. The system could recover >70% of the carbon from raw wastewater, whereas the concentration of chemical oxygen demand in the effluent was lowered to <20 mg/L. The performance of the proposed HR-MBR observed in this study was clearly superior to those reported in previous related studies.

Efficient ammonia-nitrogen removal and recovery from wastewater via the continuous flat-sheet gas-permeable membranes reactor pretreatment

Ammonia‑nitrogen is a crucial component of landfill leachate and a major factor in the eutrophication of aquatic bodies. A novel approach was developed using the continuous flat-sheet gas-permeable membranes (GPMs) reactor pretreatment to efficiently remove and recover ammonia‑nitrogen. The total ammonia‑nitrogen removal efficiency reached 74.2 ± 4.5 % and 66.2 ± 4.9 %, respectively, when simulated nitrogenous wastewater and landfill leachate were treated under the following conditions: influent flow rate 25 L/d, pH 11.0, temperature 25 °C, sulfuric acid absorption concentration 2.5 %, and sulfuric acid absorption flow velocity 70 mL/min. In addition, (NH4)2SO4 (i.e., a crucial ammonia resource) was recovered efficiently, and the flat-sheet GPMs exhibited stable hydrophobic properties. Specifically, the combination of membrane pretreatment and biological treatment reduced the ammonia‑nitrogen concentration from ~230 mg/L (with direct biological treatment only) to ~40 mg/L, with the removal efficiency benefitting from the increase in the chemical oxygen demand/total ammonia nitrogen (COD/TAN) ratio of the leachate after membrane pretreatment. Furthermore, microorganisms that are capable of ammonia‑nitrogen removal (Planktosalinus and Rheinheimera) were selectively enriched. Overall, this study provides a practical method to enhance ammonia‑nitrogen removal and recovery for the treatment of wastewater containing high ammonia‑nitrogen concentrations.

Enhanced Antifouling in Flat-Sheet Polyphenylsulfone Membranes Incorporating Graphene Oxide-Tungsten Oxide for Ultrafiltration Applications.

In this study tungsten oxide and graphene oxide (GO-WO2.89) were successfully combined using the ultra-sonication method and embedded with polyphenylsulfone (PPSU) to prepare novel low-fouling membranes for ultrafiltration applications. The properties of the modified membranes and performance were investigated using Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), contact angle (CA), water permeation flux, and bovine serum albumin (BSA) rejection. It was found that the modified PPSU membrane fabricated from 0.1 wt.% of GO-WO2.89 possessed the best characteristics, with a 40.82° contact angle and 92.94% porosity. The permeation flux of the best membrane was the highest. The pure water permeation flux of the best membrane showcased 636.01 L·m-2·h-1 with 82.86% BSA rejection. Moreover, the membranes (MR-2 and MR-P2) manifested a higher flux recovery ratio (FRR %) of 92.66 and 87.06%, respectively, and were less prone to BSA solution fouling. The antibacterial performance of the GO-WO2.89 composite was very positive with three different concentrations, observed via the bacteria count method. These results significantly overtake those observed by neat PPSU membranes and offer a promising potential of GO-WO2.89 on activity membrane performance.

Development of CuCo2O4 integrated ceramic membrane for peroxymonosulfate activation: An efficient oxidation process for bisphenol A degradation

In this study, a new functionalized flat-sheet ceramic membrane (CuCo2O4-CM) was prepared by an impregnation-calcination strategy and used in the removal of Bisphenol A (BPA). Various characterization results indicated that a CuCo2O4 layer was uniformly anchored on the membrane surface and the internal porous channels. The CuCo2O4-CM possessed a smaller mean pore size (80 nm) and better hydrophilicity than the pristine α-Al2O3 substrate after modification. The catalytic degradation in CuCo2O4-CM /PMS system revealed that 92.1% of BPA and 70.0% of TOC could be removed under optimal conditions (pH = 7.0, CBPA = 30 mg/L and CPMS = 2 mM). Meanwhile, the membrane showed good reusability and improved antifouling properties. During the reaction, four reactive oxygen species (·OH, SO4·-, O2·- and 1O2) were generated and they all responded for the degradation of BPA. In addition, the mechanism of PMS activation and BPA degradation were proposed. This study presented an efficient oxidation process for BPA degradation and outlines the synergistic effect of separation and catalytic oxidation.

Thin-Film Composite Matrimid-Based Hollow Fiber Membranes for Oxygen/Nitrogen Separation by Gas Permeation.

In recent years, the need to reduce energy consumption worldwide to move towards sustainable development has led many of the conventional technologies used in the industry to evolve or to be replaced by new alternatives. Oxygen is a compound with diverse industrial and medical applications. For this reason, obtaining it from air is one of the most interesting separations, traditionally performed by cryogenic distillation and pressure swing adsorption, two techniques which are very energetically expensive. In this sense, the implementation of membranes in a hollow fiber configuration is presented as a much more efficient alternative to carry out this separation. The aim of this work is to develop cost-effective multilayer hollow fiber composite membranes made of Matrimid and polydimethylsiloxane (PDMS) for the separation of oxygen and nitrogen from air. PDMS is used as a cover layer but can also enhance the performance of the membrane. In order to compare these two materials, three different configurations are studied. First, integral asymmetric Matrimid hollow fiber membranes were produced using the spinning method. Secondly, by using dip-coating method, a PDMS dense selective layer was deposited on a self-made polyvinylidene fluoride (PVDF) hollow fiber support. Finally, the performance of a dual-layer hollow fiber membrane of Matrimid and PDMS was studied. Membrane morphology was characterized by SEM and separation performance of the membranes was evaluated by mixed-gas permeation experiments. The novelty presented in this work is the manufacture of hollow fiber membranes and the way Matrimid is treated. This makes it possible to develop much thinner dense layers than in the case of flat-sheet membranes, which leads to higher permeance values. This is a key factor when implementing this technology on an industrial scale. Membranes prepared in this work were compared to the current state of the art, reporting quite good performance for the dual-layer membrane, reaching O2 permeance of 30.8 GPU and O2/N2 selectivity of 4.7, with a thickness of about 5-10 μm (counting both selective layers). In addition, the effect of operating temperature on the membrane permeances has been studied experimentally; we analyze its influence on the selectivity of the separation process.

Preparation and characterization of PPO/ SiO2 mixed matrix membrane for CO2 separation using membrane contactor

This study presents CO2 separation using PPO/SiO2 mixed matrix membranes (MMMs) in a membrane contactor. The non-solvent induced phase separation (NIPS) method was used to prepare flat sheet membranes using a commercial grade of PPO (polyphenylene oxide) polymer and 2-Ethyl-1-hexanol as a non-solvent additive. Mixed matrix membranes were fabricated via two approaches; adding the hydrophobic silica into casting solution (approach 1) and into coagulation bath (approach 2). The results showed that the addition of 2-ethyl-1-hexanol (5wt%) to the casting solution improved the membrane porosity by 74.7% while reducing the contact angle from 106.3 to 95.2°. Water contact angle of prepared MMMs by approaches 1 and 2 were found to be around 117.8 and 142.9°, respectively indicating that silica could enhance the membrane hydrophobicity in both methods. The maximum CO2 absorption flux and removal efficiency were attained about 5.8 × 10−3 (mol.m−2.s−1) and 64.8 % for MMM with 2 wt.% silica in approach 1. Meanwhile, MMM obtained with silica content (2 g.L−1) from approach 2, indicated CO2 flux of 5 × 10−3 (mol.m−2.s−1) and removal efficiency around 55.8 %. The long-term performance of prepared MMMs was evaluated during 20 days of operation. The results confirmed the long term stability of prepared samples and good interaction between the silica particles and the PPO polymer in scenario of approach 2.

Detailed numerical analysis of air gap membrane distillation performance using different membrane materials and porosity

The motivation of this computational research is to comprehensively analyze the performance of the air gap membrane distillation (AGMD) process by varying the membrane porosity at different inlet feed temperatures (Tfeed) in counter-current and co-current flow regimes. This computational study also includes the comparative study of different membrane materials with different porosities. In this research work, a detailed theoretical model for porous medium with phase change is formulated and presented to evaluate the permeate mass flux, heat flux, and evaporation efficiency of the AGMD technique. Additionally, a CFD numerical model is successfully developed and validated with the previously published data.The results reveal that high evaporation efficiency is achieved at about 90 %, 92 %, and 94 % with 90 % membrane porosity at different inlet feed temperatures of 50 °C, 60 °C, and 75 °C, respectively, in both flow regimes. Also, transported mass flux was enhanced by 43 % at Tfeed, 50 °C with high porosity, while it increased by 65 % at Tfeed, 75 °C. The AGMD thermal performance using PVDF and PTFE flat sheet membranes is comparable with the same membrane thickness and at the same porosity; however, PTFE offers relatively high evaporation efficiency and mass flux, especially at low inlet feed temperature (50 °C).

Synergistic effects of silica derived granite dust and MoS2 on oil-water separation performances of mixed matrix PES membrane

Membrane separation technology has been widely examined for the treatment of oily wastewater owing to its numerous advantages, including high efficiency, energy saving, compact structure, and ease of operation. However, the overall performance of membrane separation highly depends on the membrane properties such as hydrophilicity and morphology structure. Nanoparticles (NPs) have been widely used to increase membrane hydrophilicity and fouling resistance. In this work, silica derived from granite dust (GD) via the sol–gel method was hydrothermally treated with molybdenum disulfide (MoS2) and used for the fabrication of MoS2-silica-PES mixed matrix membranes (MMMs). The synthesis of MoS2-silica composite was first confirmed via XRD analysis. Then, 1.0 wt% of MoS2-silica was blended into the PES casting solution, and the flat sheet membrane was cast by controlling the thickness of about 100 μm. The MoS2-silica-PES MMMs were then subjected to chemical, hydrophilicity and surface morphology studies. It was found that the addition of silica into MoS2 leads to a notable improvement in hydrophilicity and water flux as compared to bare PES and MoS2-PES membranes. The performance of MoS2-silica-PES membrane was then evaluated for oil–water separation using 1000 ppm oil concentrations at 1 bar and room temperature. The membrane was first compacted for 2 h at 2 bar before the oil–water separation test to maintain a stable flux. It was found that there was a substantial increase in the oil–water flux of the composite membranes (from 3.25 LMH to 41.68 LMH) when silica was added. This was due to the enhancement in membrane properties and morphology structure. Generally, the oil rejection of the MoS2-silica-PES MMMs fabricated in this work was maintained above 95 %. This study indicates that the fabricated MoS2-silica-PES MMMs have excellent potential for commercial applications. Using silica-derived granite dust offers an opportunity to lower the cost of the membrane.

Screening and Scale-up of Nanofiltration Membranes for Concentration of Lactose and Real Whey Permeate.

In dairy industry huge quantities of whey accumulate as a by-product. In particular the containing lactose was not produced profitably in the past. Thus, the trend goes towards modification and sustainable use of lactose for which a concentration step is required. Nanofiltration (NF) has shown to be a good choice since partial demineralization can be realized in parallel. Therefore, in this study, 10 commercial polymer NF membranes were studied in detail and systematically for their suitability to concentrate lactose, with the proviso of high flux and high to complete rejection. Preliminary trials were conducted with flat-sheet membranes and a lactose model solution and the influence of transmembrane pressure (TMP), temperature and lactose concentration was studied. Finally, results were evaluated by using spiral wound modules and real industrial whey permeate. The results offered that a membrane screening is essentially since no correlation between molecular weight cut-off (MWCO) and permeate flow could be found. The conclusions found for the lactose model solution were in good agreement with the whey permeate, but as the ions contribute to the osmotic pressure of the feed the deviations increase in the course of concentration since ions are also partly retained.

New insights into membrane fouling during direct membrane filtration of municipal wastewater and fouling control with mechanical strategies

Direct membrane filtration (DMF) technology achieves energy self-sufficiency through carbon recovery and utilization from municipal wastewater. To control its severe membrane fouling and improve DMF technology, targeted research on fouling behaviour and mechanisms is essential. In this study, a DMF reactor equipped with a flat-sheet ceramic membrane was conducted under three scenarios: without control, with intermittent aeration, and with periodic backwash. This system achieved efficient carbon concentration with chemical oxygen demand below 50 mg/L in permeate. Membrane fouling was dominated by intermediate blocking and cake filtration. And reversible external resistance accounted for over 85 % of total resistance. Predominant membrane foulants were free proteins, whose deposition underlies the attachment of cells and biopolymers. Backwash decreased the fouling rate and increased fouling layer porosity by indiscriminately detaching foulants from the membrane surface. While aeration enhanced the back transport of large particles and microbial activity, causing a relatively thin and dense fouling layer containing more microorganisms and β-d-glucopyranose polysaccharides, which implies a higher biofouling potential during long-term operation. In addition, aeration combined with backwash enhanced fouling control fivefold over either one alone. Therefore, simultaneous operation of backwash and other mechanical methods that can provide shear without stimulating aerobic microbial activity is a preferred strategy for minimizing membrane fouling during DMF of municipal wastewater.

Development of Fouling-Control Strategy for Ceramic Membrane Bioreactor Applied in Partial Nitrification Process

A lab-scale ceramic membrane bioreactor (MBR) with active membrane-fouling control system was developed for the partial nitrification (PN) process. The in situ membrane cleaning method was applied to remove the contaminants on the surface of the membrane with no interruption of the wastewater treatment. The results showed that the device increased critical flux and reduced gel layer resistance (Rg) and internal resistance (Ri) of the flat-sheet ceramic membrane by inhibiting the formation of the cake layer. In long-term experiments, nitrite oxidizing bacteria (NOB) was successfully suppressed, and nitrite accumulation rate (NAR) was achieved at a high level, up to 90.09%; the effluent NO2−-N/NH4+-N was maintained in balance dynamically with an average ratio of ~1.30, which would be beneficial to the proliferation of Anammox bacteria and the following autotrophic nitrogen removal (ANR) process. Moreover, with the assistance of in situ cleaning, energy input from aeration was significantly reduced, while over aeration was avoided for more stable PN performance.

Key Parameters Impacting the Crystal Formation in Antisolvent Membrane-Assisted Crystallization.

Antisolvent crystallization is commonly used in the formation of heat-sensitive compounds as it is the case for most active pharmaceutical ingredients. Membranes have the ability to control the antisolvent mass transfer to the reaction medium, providing excellent mixing that inhibits the formation of local supersaturations responsible for the undesired properties of the resulting crystals. Still, optimization of the operating conditions is required. This work investigates the impact of solution velocity, the effect of antisolvent composition, the temperature and gravity, using glycine-water-ethanol as a model crystallization system, and polypropylene flat sheet membranes. Results proved that in any condition, membranes were consistent in providing a narrow crystal size distribution (CSD) with coefficient of variation (CV) in the range of 0.5-0.6 as opposed to 0.7 obtained by batch and drop-by-drop crystallization. The prism-like shape of glycine crystals was maintained as well, but slightly altered when operating at a temperature of 35 °C with the appearance of smoother crystal edges. Finally, the mean crystal size was within 23 to 40 µm and did not necessarily follow a clear correlation with the solution velocities or antisolvent composition, but increased with the application of higher temperature or gravity resistance. Besides, the monoclinic form of α-glycine was perfectly maintained in all conditions. The results at each condition correlated directly with the antisolvent transmembrane flux that ranged between 0.0002 and 0.001 kg/m2. s. In conclusion, membrane antisolvent crystallization is a robust solution offering consistent crystal properties under optimal operating conditions.

Effect of solvents in the formation of PES-based asymmetric flat sheet membranes in phase inversion method: phase separation and rheological studies

Effect of solvents in the formation of PES-based asymmetric flat sheet membranes in phase inversion method: phase separation and rheological studies

Integration of Ultra- and Nanofiltration for Potato Processing Water (PPW) Treatment in a Circular Water Recovery System.

The article analyzes integrated ultrafiltration (UF) and nanofiltration (NF) processes for potato processing wastewater treatment for the purpose of which a laboratory filtration system for flat sheet membranes with the effective surface area of 1.4 × 10-2 m2 (UF: polysulfone, cut-off: 10,000 Da; NF: polypiperazine amide, cut-off: 150-300 Da) was used. As part of the study, the effect of the transmembrane pressure of UF (0.2 MPa and 0.4 MPa) and NF (1.0 MPa and 1.8 MPa) on the permeate flux and rejection coefficient was investigated and the impact of sewage preparation methods on the degree of pollution reduction was determined. Moreover, a method for a fouling layer removal from the UF membranes is also proposed. The results of the analyses conducted by the authors show that the pretreatment stage offers additional advantages to TSS and turbidity removal. In both cases (0.2 and 0.4 MPa), UF used after the pretreatment process resulted in a 97-99% reduction in these impurities. The analysis of the determined rejection coefficients shows that the use of NaOH and H2O2 for the regeneration of the UF membrane has a positive effect on filtration efficiency. Regarding NF, the rejection coefficients for most tested parameters were higher for the 1.8 MPa process compared to 1.0 MPa, and approximately 80% of water was recovered.

Aquaporin-inspired thin–film composite nanofiltration ceramic hollow fiber with the modification of arginine

The interfacial polymerization (IP) process has been widely applied for nanofiltration membranes and thin film composite (TFC) membranes due to its high selectivity and flexibility. The performance of polyamide (PA) TFC membranes can be affected by many factors, including the selection of monomers, additives, and substrates. Arginine (Arg) is an amino acid used as the building block of aquaporin in the human cell. It acts as a potential additive for the IP process because arginine is widely known for its high hydrophilicity and zwitterionic amphiphiles in the water transport of aquaporin. Compared to flat sheet membranes, alumina hollow fibers have the advantages of organic solvent resistance, high-temperature resistance, high packing density, prominent hydrophilicity and a narrow pore size distribution. In this study, a PA TFC membrane was fabricated on an alumina hollow fiber substrate by the polyamide IP process with the addition of Arg. The Arg addition led to higher stability for the IP process of PA membranes. When 0.15 wt% Arg was added, the maximal recorded permeate flux was 22.09 ± 0.41 LMH/bar with outstanding retention of commercial dyes, including methylene blue (98.23 ± 0.41%), methyl orange (99.96 ± 0.03%), Victoria Blue B (99.72 ± 0.25%) and Evans blue (99.65 ± 0.49%). Hence, the as-prepared membrane demonstrates potential industrial application to reject positively and negatively charged dyes with smaller molecular weights.

Process optimization for fabrication of PVDF - TiO2 hydrophobic membrane using phase inversion method for desalination application using VMD

The properties of membranes are significantly influenced by process parameters. To understand the impact of operating parameters on membrane characteristics, a design of experiments was conducted using response surface methodology (RSM). The gradient descent method was employed to determine the optimal conditions for desired membrane characteristics. This study involved the preparation of a hydrophobic flat sheet membrane made of Polyvinylidene fluoride (PVDF) using central composite design (CCD) arrays. The operating variables considered for developing the PVDF flat sheet hydrophobic membrane were polymer concentration, additive concentration, evaporation time, and ethanol concentration in the coagulation bath. The responses, such as contact angle, membrane porosity, and tensile strength, were measured using the sessile drop method, gravimetric method, and universal testing machine. Nonlinear regression models were developed for contact angle, porosity, and tensile strength using minimization of the sum of square errors in CCD, which were found to be in good agreement with experimental data. The results indicated that polymer concentration had the highest synergistic influence on the surface contact angle, but had an antagonistic effect on membrane porosity. The tensile strength of the fabricated membrane increased with polymer concentration but declined with additive concentration. It was important to determine the optimal conditions for the trade-off between the operating parameters and membrane characteristics. The theoretical desired membrane characteristics were determined to be 109 ± 2°, 59.9 ± 2%, and 78.7 ± 1 MPa under optimal conditions of 16.0 wt% polymer concentration, 1.676 wt% TiO2 concentration, 29.09 min of evaporation time, and 39.59 wt% coagulation bath concentration. The experimental values of membrane characteristics under optimal conditions were measured to be 108.2 ± 2°, 58.9 ± 2 %, and 77.3 ± 1 MPa. The fabricated membrane was employed for desalination using vacuum membrane distillation.

Are green solvents truly green? Integrating life cycle assessment and techno-economic analysis for sustainable membrane fabrication

This analysis integrates life cycle assessment and techno-economic analysis to examine the impacts of solvent selection and synthesis approaches in fabricating 1 m2 of polyimide flat sheet membrane.

Green synthesis of iron-ore flat sheet membrane and physicochemical characterization

Green synthesis of iron-ore flat sheet membrane and physicochemical characterization