Clarification of pomegranate juice by microfiltration with PVDF membranes

Microfiltration was used to clarify pomegranate juice using two polyvinylidene fluoride membranes with pore sizes of 0.22 and 0.45 μm. Changes were studied in the chemical properties of the juice after passing through each membrane. Characteristics such as turbidity changed for both membranes (more than 95%). The permeate flux decreased over time as a result of membrane fouling. The degree of decline in the membrane with pore size of 0.22 μm was greater than another one. In both membranes, fouling resistance increased over time from 5 × 10⁹ m²/kg to 4.43 × 10¹⁰ m²/kg for 0.22 μm and to 1.29 × 10¹⁰ m²/kg for 0.45 μm after 45 min. This increase had a sharp slope in the first stages of the testing. Fouling index changes over time showed similar behavior. Scanning electron microscopy images showed that the cake layer had the greatest impact on membrane fouling after processing by preventing turbid components from entering pores.     

Novel high performance hollow fiber ultrafiltration membranes spun from LiBr doped solutions

The objective of this research is to evaluate the performance of the polyethersulfone (PES) hollow fiber ultrafiltration membranes spun from LiBr doped solutions prepared using the newly developed microwave heating technique. In addition the resultant hollow fiber membranes were introduced to a new post-treatment method where the membranes were placed in water and irradiated using the microwave technique. Various concentrations of the additive, LiBr, (1-4 wt.%) were added into the PES dope solutions. The dissolution of PES and LiBr in DMF was facilitated by the microwave heating technique. The performance of the membranes was evaluated in terms of pure water permeation and polyethylene glycol separation and its molecular weight cutoff (MWCO) was determined. The results revealed that the microwave post-treatment technique was proven to be effective in producing higher performance membranes. The best performance was obtained at 3% LiBr with MWCO at 90% rejection in the range of 2.83 kDa and high flux range of 222.18 (Lm^− 2 h^− 1 bar^− 1). LiBr interacts in the membrane matrix resulting in the enhancement of the hydrophilic property of the membrane and this is confirmed by the contact angle measurement.     

Ceramic membrane behavior in textile wastewater ultrafiltration

Textile industries are rated as the most polluting among all industrial sectors taking into account both wastewater volume and composition. In order to be able to reuse these effluents, membrane technologies have been proven as a viable alternative. However, these technologies show some drawbacks, such as the retentate stream management and the worsening of their performance due to membrane fouling. Therefore, effluents must be pre-treated in order to prevent fouling. Membrane technologies also provide some alternatives for these pre-treatments by means of the application of ceramic ultrafiltration among others.This work studies the performance of ceramic membranes by carrying out experiments with three commercial ceramic membranes with molecular weight cut-offs (MWCO) of 30, 50 and 150 kDa, respectively. Moreover, the effect of cross-flow velocity (CFV) was studied by performing the essays at different flow velocities of 3, 4 and 5 m/s.According to the obtained results, ceramic UF membranes proved to be a feasible pre-treatment alternative. Permeate flux increased as flow velocity was increased for most of the cases, owing to the fact that the cake layer formation was limited. Furthermore, flux decline along operating time was negligible for the higher flow velocities, whereas it was noticeable for the lowest flow velocity tested. For the lowest MWCO analyzed, lower cross-flow velocities were needed in order to limit the cake layer formation and reach the steady-state. This implies that, although fouling was significant for all the three molecular weight cut-off studied, it was much more noticeable when MWCO was increased. Slightly better results in terms of permeate quality were achieved as MWCO was lower. In addition, higher chemical oxygen demand (COD) and conductivity retention coefficients were obtained for the lowest cross-flow velocity. Turbidity and color removals seemed to be more influenced by water composition than CFV, with rejections higher than 99% and between 84 and 98%, respectively.     

Experimental study on physical properties and pervaporation performances of polyimide membranes

Five kinds of polyimide membranes have been synthesized from two dianhydrides (including pyromellitic dianhydride (PMDA) and 3, 3^′4, 4^′-benzophenonetetracarboxylic dianhydride (BTDA)) and three diamines (including 4,4^′-diaminodiphenylether (ODA), 4,4^′-diaminodiphenylmethane (MDA) and phenylenediamine (PDA)) via a two-step method, and the properties of polyimide membranes have been characterized by experimental techniques. The permeation experiments of water/ethanol mixtures through the polyimide membranes were carried out at 318, 328, 338 and 348 K. All polyimide membranes in this paper are water selectivity, and the flux of mixtures through MDA-based polyimide membranes is higher than that of solvents through PDA-based polyimide membranes with the same diahydrides, while the separation factor exhibits the opposite variation order at the same temperature. The total flux and the partial water flux through all the membranes increase with the operating temperature rising, and the relationships between the flux and temperature can be described by Arrhenius equation. According to the Arrhenius equation, the active energies of water/ethanol in PMDA-ODA, PMDA-MDA, BTDA-PDA, BTDA-ODA and BTDA-MDA membranes are 35.1, 52.6, 16.4, 19.8 and 27.1 kJ/mol, respectively, and those for partial water flux in PMDA-ODA, PMDA-MDA, BTDA-ODA and BTDA-MDA are 36.1, 46.8, 19.9 and 27.9 kJ/mol, respectively. The separation factors of mixtures in the polyimide membranes but no PMDA-MDA show the trend of increase with the operating temperature. The partial flux of ethanol increases while the separation factor of mixtures in PMDA-MDA decreases with the operating temperature, and the activation energy for partial ethanol flux in PMDA-MDA is 75.2 kJ/mol. In addition, pervaporation performances were attempted to correlate independently with the fractional free volume (FFV) and mean interchain distance (d-spacing) of polymers. It is shown that lnJ increases with d-spacing, while there is no clear relationship between the flux and FFV.     

Studies on fouling by natural organic matter (NOM) on polysulfone membranes: Effect of polyethylene glycol (PEG)

Polysulfone membranes were prepared via phase inversion technique by using polyethylene glycol with molecular weights of 400, 1500 and 6000 Da as pore forming agent in dope formulation. The performance of membrane was characterized using humic acid and water sample taken from Sembrong River, Johor, Malaysia was used as natural organic matter sources. Membrane properties were also characterized in terms of mean pore radius, pure water flux, humic acid rejection and fouling resistance. The results indicated that the pure water flux and mean pore radius of membranes increased with the increase of PEG content. Fourier transform infrared spectroscopy results revealed the presence of hydrophilic component in PSf/PEG blend with the significant appearance of O–H peak at 3418.78 cm^− 1. Scanning electron microscopy analysis revealed the presence of finger-like structure for all membranes and the structure intensified as PEG content was increased. The results obtained from the fouling study indicated that the membrane with the lowest PEG content and molecular weight has an excellent performance in mitigating fouling.     

Dehydration of ethylene glycol by pervaporation using gamma alumina/NaA zeolite composite membrane

High-quality zeolite NaA membranes were synthesized on modified α-alumina supports. The surface of macroporous α-alumina supports was modified by deposition of an ultrafiltration layer of γ-alumina. The zeolitic top layers were synthesized via the secondary growth method. The required seeds for the membrane synthesis were prepared via the hydrothermal synthesis using organic template of tetra methyl ammonium hydroxide (TMAOH) to obtain nano-sized seeds. The synthesized seeds and membranes were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The separation performance of membranes was evaluated in pervaporation (PV) dehydration of ethylene glycol (EG). Effect of operational parameters including feed composition, feed flow rate, and feed temperature on separation performance of the synthesized NaA zeolite membranes were investigated. The membranes showed separation factor of 10,996 and high total flux of 7.16 kg m⁻² h⁻¹ for feed temperature of 80 °C, feed flow rate of 1.5 L/min, and feed concentration of 90 wt.% EG.     

Interaction mechanisms associated with organic colloid fouling of ultrafiltration membrane in a drinking water treatment system

The Extended Derjaguin Landau Verwey Overbeek (XDLVO) approach was introduced to predict organic colloid fouling of membranes in an initial ultrafiltration (UF) phase. Two polymeric UF membranes, made of polyvinylchloride (PVC) and polyvinylidene fluoride (PVDF) respectively, were selected to investigate membrane fouling by filtering water samples with different organic colloid compositions. The experiment was performed to determine the fouling contributions of van der Waals (LW) interactions, electrostatic (EL) interactions, as well as double layer and short-range acid–base (AB) interactions, to the total interaction energy caused by organic colloids attaching to UF membrane surfaces. The results showed that LW interaction energy predominated when the distance between the membrane surface and organic colloid was > 5 nm, while AB accounted for a key contribution to total interaction energy over short distances (< 2.5 nm). The influence of EL interaction energy was ignored in the total interaction energy composition. The surface energy, among all characteristics of membrane material, was a dominant factor affecting membrane fouling. The experimental results of initial ultrafiltration of raw water from the actual water source were in accordance with the predictions based on XDLVO theory, indicating that it was a feasible option for predicting membrane fouling during the initial ultrafiltration phase.     

Nanocrystalline cellulose reinforced PVDF-HFP membranes for membrane distillation application

Polyvinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) membranes containing different amounts of nanocrystalline cellulose (NCC) were fabricated by electrospining technique for application in membrane distillation (MD). The effect of incorporating NCC on the mechanical strength, morphology, pore size distribution, and liquid entry pressure (water) of the fibrous was investigated. Incorporation of NCC in PVDF-HFP matrix improved the tensile strength and Young's modulus and narrowed down the pore size distribution of the fabricated membranes. Liquid entry pressure, which is an important parameter to ensure high salt rejection of the membranes in MD, was improved from ~ 19 psi to ~ 27 psi with the addition of 2 wt.% NCC. Fabricated membranes were tested in direct contact membrane distillation (DCMD). MD operation data revealed water flux of 10.2–11.5 Lh^− 1 m^− 2 with salt rejection of 99% for these NCC-incorporated membranes.     

Influence of lithium chloride, lithium bromide and lithium fluoride additives on performance of polyethersulfone membranes and its application in the treatment of palm oil mill effluent

In this study three different types of lithium halides; lithium bromide (LiBr), lithium chloride (LiCl) and lithium fluoride (LiF) were used as additives in the making of polyethersulfone (PES) membranes. The concentration of PES is kept constant at 20 wt.% throughout the study, and the lithium halide concentration is varied in the range of 1-5 wt %. The solvent used is N, N-dimethylformamide and the PES asymmetric membrane was prepared by the dry/wet phase inversion process. Membrane performance was characterized in terms of pure water permeation (PWP), permeation rate (PR) and solute separation of polyethylene glycol (PEG) solution of various molecular weights ranging from 600 to 35,000 Da. The molecular weight cut off (MWCO) and mean pore size distribution were subsequently determined. Results revealed that the 3 wt.% LiBr exhibits the best performance with MWCO at 90% rejection in the range of 2.83 kDa and high flux range of 117.69 L m^− 2 h^− 1. Hollow fibers spun from the dope solutions containing LiBr revealed that they are capable of treating palm oil mill effluent (POME) with reduction in turbidity, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) of 96.7%, 53.12% and 76.7% respectively.     

Fouling of UF membrane by humic substance: Effects of molecular weight and powder-activated carbon (PAC) pre-treatment

Fouling characteristics of membranes with various molecular weight cut-offs (MWCO) were investigated. The effects of the molecular weights (MW) of humic acids and pre-treatment with PAC on membrane fouling were studied. It was found that the hydraulic resistance caused by fouling materials calculated using cake resistance in series model is a better indicator than the percentage of flux decline to assess the fouling of membranes with various MWCO. The effects of MWCO of membranes and MW of humic acids on membrane fouling can be explained by the different types of fouling mechanisms.     

Preparation,characterization and performance of cellulose acetate ultrafiltration membranes modified by charged surface modifying macromolecule

A charged surface modifying macromolecule (cSMM) was synthesized, characterized by FT-IR spectroscopy and blended into the casting solution of cellulose acetate (CA) to prepare surface modified UF membranes by phase inversion technique. With an increasing cSMM additive content from 1 to 4 wt%, pure water flux (PWF) and water content (WC) were increases whereas the hydraulic resistance decreases. Surface characteristic study reveals that the surface hydrophilicity increased in cSMM modified CA membranes. The pore size and surface porosity of the 4 wt% cSMM blend CA membranes increases to 41.26 Å and 0.015%, respectively. Similarly, the molecular weight cut-off (MWCO) of the membranes ranged from 20 to 45 kDa, depending on the various compositions of the prepared membranes. Lower flux decline rate (47.2%) and higher flux recovery ratio (FRR) (89.0%), exhibited by 4 wt% cSMM blend membranes demonstrated its fouling resistant characteristic compared to pristine CA membrane.     

Flux recovery of tubular ceramic membranes fouled with whey proteins

Membrane process efficiency is governed by the formation of fouling deposits during processing of dairy fluids. Because of fouling with whey proteins, permeate flux can drastically decline during filtration process. This paper describes the flux recovery procedure for ceramic tubular membranes (50 and 200 nm pore sizes) fouled with whey proteins. The results comprehend the effect of rinsing and cleaning agent choice and concentration, on the cleaning efficiency. As chemical cleaning agents, the caustic solution and the commercial detergents P3-ultrasil 67 and P3-ultrasil 69 were selected. The observations are that rinsing with deionised water contributes to a flux recovery to a certain degree. For the 50 nm membrane, the choice of the 1.0% (w/w) caustic solution, as cleaning agent, gives the best flux recovery. For the 200 nm, total flux recovery was not observed regardless of the cleaning agent choice and concentration. Cleaning with chosen commercial detergent appeared to be less efficient than cleaning with caustic solution for the chosen ceramic membranes. Also, a mathematical model, proposed in this study, has shown high agreement with experimentally obtained data.     

Primary study of novel poly(acrylic sodium)/poly(ether sulfone) composite ultrafiltration membranes (I) the preparation of composite membrane

The poly(acrylic sodium) (PAS)/poly(ether sulfone) (PES) composite ultrafiltration membranes were prepared by coating PAS membrane solution on PES support membrane. The effects of substrate membrane, the composition of PAS solution such as PAS concentration, the choice of the solvent and the additive, and the thickness of PAS active layer on the performance of the composite membranes were extensively investigated. The experimental results have indicated the optimal PAS/PES composite membranes, containing a PES substrate with MWCO of 70,000, together with a PAS top layer having a thickness of about 20 μm, were tested at room temperature and under the pressure of 0.6 MPa with the mass concentration of 0.005 g/L poly(ethylene glycol) (PEG) (Mw = 1000 g/mol) solution, a flux of 32.6 L/(m² h) and a rejection of 92.2% were obtained, which are superior to those of the common commercial membranes reported.     

A comparative study of tertiary membrane filtration of industrial wastewater treated in a granular and a flocculent sludge SBR

Membrane fouling has been identified by many researchers as an inconvenience for the industrial application of membranes in wastewater treatment plants. Membrane fouling decreases permeability and therefore permeates flow, increasing costs. Although fouling is the result of complex phenomena not completely known, it can be said that fouling takes place by the presence of three different kinds of compounds in the water: suspended solids, colloids and solutes. In this sense, the characteristics of the suspended solid aggregates might be an important aspect in order to diminish the impact of suspended solids on membrane fouling. The main objective of this study was to compare the operation of two similar tertiary membrane filtration units treating the effluent of two different SBRs, respectively: A granular sludge SBR (GSBR) and a membrane flocculent sludge SBR system, at laboratory scale. Two PVDF microfiltration membrane modules were used for tertiary filtration of the effluent treated in the SBRs. Both reactors were used for treating the wastewater generated in a factory of the fish freezing sector. COD of the wastewater was between 700 and 1100 mg/L, total nitrogen concentration was between 110 and 180 mg N/L and total phosphorus ranged around 110 mg P/L. The chemical characteristics of both permeates were similar. Moreover, the presence of either granules or flocs in the tertiary membrane filtration systems did not have an appreciable impact on the membrane filtration. Nevertheless, it was observed that the operation of the membrane on the flocculent system tends to be more instable, showing a major tendency to achieve critical flux.     

Selective separation of contaminants from paper mill effluent using nanofiltration

Biologically treated newsprint mill effluent containing 57 mg L⁻¹ DOC and 1430 TDS was used in a screening study of nine commercial NF membranes for use as pretreatment for reverse osmosis in an end of pipe water recycling application. A salt-organic-separation (SOS) efficiency factor was developed to help rank the performance of the membranes. The SOS measures the ratio of the sum of the percentage rejection of organics and divalent cations over the percentage rejection of monvalents. It can be used to discriminate between NF membranes that are not too permeable to divalent cations or organics in which case the NF permeate will have a high chlorine demand due to the carryover of organics, or too retentive in which case all the material in the effluent will be retained and fouling problems are likely to occur. The optimum SOS efficiently for this study appeared to range from 3.5 to 5.6 for six membranes, DK, HPA-150, ESNA1-LF2, DL, TFC-SR2 and NF-270, which were categorised as membranes with an intermediate rejection. Out of these membranes ESNA1-LF2, TFC-SR2 and NF-270 were capable of operating up to 90% recovery with high permeabilities ranging from 17.7 to 22.3 L m⁻² h⁻¹ bar⁻¹.     

Microporous polyvinylidene fluoride hollow fiber membrane contactors for CO2 stripping: Effect of PEG-400 in spinning dope

In order to develop the structure of microporous PVDF membranes, PEG-400 was introduced into the polymer dope as a non-solvent additive. The hollow fiber membranes were prepared via a wet phase-inversion process and then used in the membrane contactor modules for CO₂ stripping from water. By addition of different amounts of PEG-400, cloud points of the polymer dope were obtained to examine phase-inversion behavior. From FESEM analysis, the membrane structure changed from a finger-like to an approximately sponge-like morphology with the addition of 4 wt.% of PEG-400. The prepared membranes presented smaller mean pore size (0.13 μm) and significantly higher wetting pressure (550 kPa) compared to the plain membrane. From CO₂ stripping test, at water velocity of 0.4 m/s, the PVDF membranes prepared by 4% PEG-400 demonstrated an approximate CO₂ stripping flux of 4.5 × 10⁻⁵ (mol/m² s) which is 125% higher than the flux of the plain membrane. It could be concluded that structurally developed hydrophobic PVDF hollow fiber membranes can be prepared by a controlled phase-inversion process to enhance the performance of gas–liquid membrane contactor.     

Membrane choice for wastewater treatment using external cross flow tubular membrane filtration

Systematic investigations of activated sludge separation were conducted using membrane filtration. To accomplish this, different organic tubular membranes with different separation limits and diameters were examined. Furthermore, from the results obtained in the initial tests, an appropriate membrane was chosen for a long-term test. The investigations determined that for biomass separation by the tubular membranes in the tested system, neither the membrane material nor the separation limit within a range of 1 μm to 20,000 Da had a significant influence on the filtration characteristics. It was recognized that the application of a tubular membrane with a diameter of less than 8 mm is problematic, because high flow velocities were needed to prevent blockage of the membrane. When the flow velocity was in the range of 1 to 4 m/s, a linear relation between flux and velocity was found. This showed the potential for controlling the membrane filtration process and externally influencing the permeate rate. An average retention of TOC was about 75%. The retention of TOC was not significantly influenced by the nominal pore sizes of the membranes (except for the membrane WFNX 0505) which were tested here. The ultrafiltration membrane WFS 0120 (Stork) was prominent in the long-term test due to its very high flux, germfree permeate with a MWCO (molecular weight cut-off) of 100,000 Da, and was not blocked with a diameter of 14.4 mm, also at lower flow velocities. The results of the long-term test supported the hypothesis that a meaningful application of such a module concept is possible in a filtration plant for the preparation of samples or for the rejection of the biomass in small sewage treatment plants.     

Investigations on the use of different ceramic membranes for efficient oil-field produced water treatment

Efficient performance of the combination of treatment processes for oilfield produced water generated from oil tank dewatering was investigated in the study presented below. By-produced wastewater is generated in significant quantity during exploitation of crude oil and gas from onshore and offshore production operations. This wastewater, commonly referred to as “produced water”, has distinctive characteristics, due to their organic and inorganic compounds. However, these characteristics change from well to well. The treatment process investigated here consists of a pre-treatment step utilizing microfiltration (0.1 and 0.2 µm pore size filters) and/or a simulated batch dissolved air flotation (DAF), and a multistage post-treatment step utilizing cross-flow ultra- (0.05 µm pore size and 20 kDa molecular weight cut-off filters), and nanofiltration (1 and 0.75 kDa MWCO filters). Filters used were ceramic membranes. To determine the separation capability of the processes described, various parameters, such as trans-membrane pressure varying from 0.5 to 2 bar, cross-flow velocity in the range of 0.6 to 1.3 m/s, influent oil concentration ranging from 32 to 5420 parts per million (ppm) and different membrane cleaning methods used were investigated. The average permeate flux varied from 3.4 to 3300 l/h m² bar, total oil removal was up to 99.5% and total organic carbon removal reached 49%.     

Morphological and separation performance study of polysulfone/titanium dioxide (PSF/TiO2) ultrafiltration membranes for humic acid removal

In this study, polysulfone (PSF) hollow fiber membranes with enhanced performance for humic acid removal were prepared from a dope solution containing PSF/DMAc/PVP/TiO₂. The main reason for adding titanium oxide during dope solution preparation was to enhance the antifouling properties of membranes prepared. In the spinning process, air gap distance was varied in order to produce different properties of the hollow fiber membranes. Characterizations were conducted to determine membrane properties such as pure water flux, molecular weight cut off (MWCO), humic acid (HA) rejection and resistance to fouling tendency. The results indicated that the pure water flux and MWCO of membranes increased with an increase in air gap distance while HA retention decreased significantly with increasing air gap. Due to this, it is found that the PSF/TiO₂ membrane spun at zero air gap was the best amongst the membranes produced and demonstrated > 90% HA rejection. Analytical results from FESEM and AFM also provided supporting evidence to the experimental results obtained. Based on the anti-fouling performance investigation, it was found that membranes with the addition of TiO₂ were excellent in mitigating fouling particularly in reducing the fouling resistances due to concentration polarization, cake layer formation and absorption.     

Membrane fouling and chemical cleaning in water recycling applications

Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water treatment and reuse applications. Fouling strongly depends on the feed water quality, especially the nature of the foulants and ionic composition of the feed water. Consequently, appropriate selection of the chemical cleaning solutions can be seen as a critical factor for effective fouling control. In this study, membrane fouling and chemical cleaning under condition typical to that in water recycling applications were investigated. Fouling conditions were achieved over approximately 18 h with foulant cocktails containing five model foulants namely humic acids, bovine serum albumin, sodium alginate, and two silica colloids in a background electrolyte solution. These model foulants were selected to represent four distinctive modes of fouling: humic acid, protein, polysaccharide, and colloidal fouling. Three chemical cleaning solutions (alkaline solution at pH 11, sodium dodecyl sulphate (SDS), and a combination of both) were evaluated for permeate flux recovery efficiency. The results indicated that with the same mass of foulant, organic fouling was considerably more severe as compared to colloidal fouling. While organic fouling caused a considerable increase in the membrane surface hydrophobicity as indicated by contact angle measurement, hydrophobicity of silica colloidal fouled membrane remained almost the same. Furthermore, a mechanistic correlation amongst cleaning efficiency, characteristics of the model foulants, and the cleaning reagents could be established. Chemical cleaning of all organically fouled membranes by a 10 mM SDS solution particularly at pH 11 resulted in good flux recovery. However, notable flux decline after SDS cleaning of organically fouled membranes was observed indicating that SDS was effective at breaking the organic foulant—Ca²⁺ complex but was not able to effectively dissolve and completely remove these organic foulants. Although a lower permeate flux recovery was obtained with a caustic solution (pH 11) in the absence of SDS, the permeate flux after cleaning was stable. In contrast, the chemical cleaning solutions used in this study showed low effectiveness against colloidal fouling. It is also interesting to note that membrane fouling and chemical cleaning could permanently alter the hydrophobicity of the membrane surface.