Concentration of Skim Milk by a Cascade Comprised of Ultrafiltration and Nanofiltration: Investigation of the Nanofiltration of Skim Milk Ultrafiltration Permeate

In order to reach a high volume reduction ratio (VRR) prior to drying of skim milk, a membrane cascade comprising of an ultrafiltration (UF) coupled with a nanofiltration (NF) can be applied. The present study investigated the impact of processing (filtration temperature, transmembrane pressure (TMP)) and product (feed pH) parameters on the NF of skim milk UF permeate. It could be shown that a low filtration temperature of 10 °C is more advantageous in terms of flux stability and rejection of the solute fraction as compared to higher filtration temperatures up to 45 °C. The solution pH did not affect permeate flux and lactose retention. However, in order to avoid calcium losses, it is more favorable to conduct the concentration at a pH of 6.8 instead of at a lower pH of 5. The application of a higher TMP (up to 4 MPa) enhances permeate flux and VRR as well as solute rejection during concentration of UF permeate. It was also shown that the retention of solutes decreases towards the end of the concentration process. As a consequence, the achievement of high final VRR must be weighed against increased product losses at the end.     

聚醚砜超滤膜分离菜籽油/乙醇混合物的研究

用聚醚砜超滤膜分离菜籽油/乙醇混合物,研究了混合物中菜籽油质量分数(20%～60%)、操作压力(0.15～0.3 MPa)和时间(10～60 min)等参数对分离效果的影响,并探讨了该膜渗透通量的数学模型.结果表明:膜的渗透通量随着操作压力的升高而升高,随时间的延长和混合物中菜籽油质量分数的提高而降低;膜对油脂的截留率随着操作压力的升高、混合物中菜籽油质量分数的提高而降低.当操作压力为0.15 MPa、菜籽油/乙醇混合物质量分数为20%时,得到最高的油脂截留率为95.03%.     

Decolorization of vegetable oils by membrane processing

Membrane decolorization studies of chlorophyll added sunflower oil and crude soybean oil were conducted in a batch membrane cell using two polymeric composite membranes (NTGS-2100 and NTGS-1100), and one polyethylene microfiltration membrane (PE-30). NTGS-2100 membrane could remove up to 96% and 72% chlorophyll from the undiluted and oil-hexane (50 wt%) solutions, respectively. Permeate oil flux was very low when undiluted oil was used as feed, but improved many fold by diluting with hexane. NTGS-1100 membrane gave higher permeate flux compared to NTGS-2100, but showed reduced rejection. Absorbance spectra of crude soybean oil and the permeate in the 350-550 nm range showed a greater degree of decolorization by polymeric composite membranes. PE-30 membrane showed insignificant rejection of color compounds. The permeate of conventionally bleached soybean oil showed a reduction in extinction coefficients at 232 and 270 nm, indicating possible rejection of dienes and trienes by the composite polymeric membranes. The membrane process was effective in reducing the color compounds in crude vegetable oils besides offering many advantages over the conventional process.     

PROCESSING OF CRUDE PALM OIL WITH CERAMIC MICROFILTRATION MEMBRANE

Membrane separation technology offers a potential application in the processing of crude palm oil. Ceramic membranes with different pore diameters (0.45 and 0.2 micron) were used to conduct the study on micromembrane process. Quality parameters of membrane-processed oils examined included free fatty acid (FFA), carotene, fatty acid composition (FAC), phosphorus and iron contents. The effect of operating parameters such as transmembrane pressure, feed flow and time on permeate flux were evaluated. It was found that 'Ceraflo'ceramic membrane with a pore size of 0.45 micron was only able to reject 14% of phosphorus from the crude oil. Ceramic membrane with pore size of 0.2 micron showed a better phosphorus rejection of 56.8%. The permeate was found to contain 7.13 ppm of phosphorus. The 0.2 micron membrane was also able to remove more than 80% of the iron from crude palm oil. Pore sizes for both membranes were not small enough to remove other components such as FFA, and carotene. Both membranes showed a similar trend in which the permeate flux increased with transmembrane pressure and feed flow until a certain limit where the flux declined with increasing pressure and feed flow. The limits in transmembrane pressures for membrane with pore sizes of 0.45 and 0.2 micron were 1.65 and 1.25 bar, respectively. Whereas the limits in feed flow for 0.45 micron and 0.2 micron membranes were 9.2 and 9.8 L/min     

Clarification of <Emphasis Type="Italic">Jerusalem Artichoke</Emphasis> Extract Using Ultra-filtration: Effect of Membrane Pore Size and Operation Conditions

Jerusalem artichoke is an important plant for industrial inulin production. Jerusalem artichoke extract was clarified by ultra-filtration. Tests were performed to investigate effects of membrane pore size and operation conditions (trans-membrane pressure and rotation speed) on filtration kinetics and membrane-fouling mechanism. Membrane fouling was proved the main filtration resistance for a 20-kDa membrane, while concentration polarization-induced resistance was dominant for 30-, 50-, and 100-kDa membranes. Despite their similar filtration behavior, the 50-kDa membrane, compared to the 100-kDa membrane, led to less protein content (impurity) in the filtrate. Studies with the rotation speed varied from 0 to 1600 rpm and trans-membrane pressure from 0.2 to 0.4 MPa demonstrated that stirring was essential for elimination of membrane fouling. Competition of driving force and fouling was justified when trans-membrane pressure increased from 0.3 to 0.4 MPa. Filtrate analysis including protein removal, turbidity, and inulin purity revealed that ultra-filtration using the 50-kDa membrane with a trans-membrane pressure of 0.3 MPa and a rotation speed of 800 rpm was able to clarify the Jerusalem artichoke extract, removing 99% protein, and obtain a filtrate with inulin purity of 98%.     

Effect of flux (transmembrane pressure) and membrane properties on fouling and rejection of reverse osmosis and nanofiltration membranes treating perfluorooctane sulfonate containing wastewater

Perfluorooctane sulfonate (PFOS) is an emergent contaminant of substantial environmental concerns. In this study, reverse osmosis (RO) and nanofiltration (NF) membranes were used to remove this toxic and persistent compound from PFOS-containing wastewater. Five RO membranes and three NF membranes were tested at a feed concentration of 10 ppm PFOS over 4 days, and the PFOS rejection and permeate flux performances were systematically investigated. PFOS rejection was well correlated to sodium chloride rejection. The rejection efficiencies for the RO membranes were > 99%, and those for the NF membranes ranged from 90-99%. Improvement in PFOS rejection, together with mild flux reduction (< 16%), was observed at longer filtration time. Such shifts in rejection and flux performance were probably due to the increased PFOS accumulation at longer duration, as shown by X-ray photoelectron spectroscopy and liquid chromatograph and tandem mass spectrometry results. A fraction of PFOS molecules might be entrapped in the polyamide layer of the composite membranes, which hindered the further passage of both water and other PFOS molecules. In a similar fashion, PFOS rejection and fouling were enhanced for greater initial flux and/or applied pressure, where PFOS accumulation was promoted probably due to increased hydrodynamic permeate drag. Flux reduction was also shown to correlate to membrane roughness, with the rougher membranes tend to experience more flux reduction than the smoother ones.     

Cross-flow filtration of pectic substances during the enzymatic treatment of mandarin segment membranes

 This study is concerned with the cross-flow filtration of pectic substances, produced by the enzymatic treatment of membranes of mandarin segments, using several filtration membranes with pore sizes of between 0.45 μm and 30 kDa. Pectic substances solubilised in the digestion medium were polymers with an average molecular weight of 90–100 kDa. Pectin was retained by the membrane with a 100-kDa pore size. As a result of the addition of enzymes, pectin was degraded to a mixture of galacturonic acid and galacturonic acid oligomers, which appeared to be distributed between the retentate and the permeate. The final filtration rate of galacturonic acid oligomers was close to 100% when enzymes were present at the filtration membranes. In the absence of enzymes, the filtration rate ranged from 5% to 15%, and the permeation flux tended to decrease. The enzymatic treatment had an important effect on the resistances of the filtration membranes, and also caused a decrease in viscosity. These two factors were responsible for the increase in the permeate flux after the addition of enzymes, where this flux was almost as high as when filtration commenced. Received: 27 October 1997     

Selecting ultrafiltration and nanofiltration membranes to concentrate anthocyanins from roselle extract (Hibiscus sabdariffa L.)

Ten nanofiltration flat-sheet membranes and eight tight ultrafiltration membranes with nominal MWCOs ranging from 0.2 to 150 kDa were tested to concentrate anthocyanin extract from roselle. A pilot system was used, which featured a membrane cell with an effective area of 0.0155 m². Permeate fluxes were recorded for transmembrane pressures between 0.5 and 3.0 MPa, while keeping all other operating conditions constant (volumetric reduction ratio 1, 35 °C). Retention values of total soluble solids, acidity and anthocyanins increased with transmembrane pressure. With similar permeate fluxes at average transmembrane pressure, retention of anthocyanins is significantly higher for nanofiltration membranes than for ultrafiltration membranes. A membrane was then selected for an industrial trial on the basis of its flux, retention of compounds of interest and energy consumption per liter of permeate. The trial using a 2.5-m² filtration surface, could concentrate roselle extract from 4 to 25 g total soluble solids per 100 g, with 100% retention of anthocyanins. No significant damages were observed when comparing concentrate quality with the initial roselle extract.     

Soymilk concentration by ultrafiltration: effects of pore size and transmembrane pressure on filtration performance

The effects of membrane pore size and operating pressure on filtration flux, membrane fouling and solute rejections of soymilk during ultrafiltration were studied. Soymilk was concentrated from an initial level of 6.5% solid content to 20% solid content using ultrafiltration membranes. Hollow fibre cross‐flow type cartridges having molecular weight cut‐off (MWCO) as 1, 10 and 30 kDa were used in the experiments. Filtration data were satisfactorily fitted to De La Garza and Boulton's exponential model to find the exponential fouling coefficient (k) and the membrane resistance (R_m). The permeate fluxes obtained in 10 and 30‐kDa MWCO membranes were found to be approximately four times higher than that of 1‐kDa MWCO membrane, at transmembrane pressure between 100 and 240 kPa. The average flux obtained was 0.7, 3.15 and 2.7 L m^?2‐h for 1, 10 and 30‐kDa MWCO membranes, respectively. The R_m value of membranes was found to decrease as the MWCO of membranes increased and transmembrane pressure decreased. The total solid content of permeates obtained by these membranes was between 0.45% and 1.4%. Membrane‐concentrated soymilk was found to have lighter colour and almost half the value of viscosity compared with evaporated milk.     

Pretreatment of aqueous pectin solution by cross‐flow microfiltration: analysis of operational parameters,degree of concentration and pectin losses

Obtaining pectin through traditional precipitation processes requires a large amount of organic solvent. A reduction in solvent consumption may be achieved by incorporating a cross‐flow microfiltration step in which the extraction solution is removed and pectin is concentrated. In this study, we used α‐alumina tubular membrane (0.44 μm) in two operation modes: total recycle mode to evaluate the effect of temperature, initial concentration of pectin and transmembrane pressure on the permeate flux and pectin coefficient rejection; and batch mode to evaluate the degree of concentration and loss of pectin. It was observed that pectin coefficient rejection varied from 93.4 ± 0.7% to 97.8 ± 0.3%, and a maximum permeate flux of 238.69 ± 6.48 kg m^?2 h^?1 with 0.12 MPa at 50 °C and 1.0 g kg^?1. Using the optimum conditions, the flux observed at the end of the process was 32.8% lower than the flux in the total recycle mode, enabling a final concentration of pectin in the retained solution of 61.04 ± 0.87% with an average pectin loss in the permeate stream of 8.18%.     

Efficient degumming of crude canola oil using ultrafiltration membranes and bio-derived solvents

Vegetable oils derived from rapeseed and its genetic variant canola, are conventionally extracted from oilseeds by means of an organic solvent, typically hexane. Concerns regarding the toxicity of hexane have meant safer and more environmentally friendly solvents such as terpenes are becoming attractive. In this research, the degumming of canola oil/terpene mixtures using ultrafiltration is considered as a critical step in such an extraction process. Polysulfone (PSF) and polyethersulfone (PES) membranes were found to be ineffective in this application, as the oil appeared to cause swelling of the membrane structure. This meant that the original flux could not be restored after cleaning. Conversely, a ceramic membrane (MWCO 5 kDa) provided stable behaviour over several cycles of operation when cleaned with pure solvent at high cross-flow velocity at 40 °C. This membrane showed high phospholipid retention (95 ± 2%), although some oil was also retained (16 ± 3%). Cymene emerged as the most attractive of the three terpenes tested, with higher permeate flux and phospholipid rejection than limonene or pinene.Industrial relevanceWhile hexane has been traditionally used for oilseed extraction, toxicity concerns are likely to restrict its industrial use in the future. This article provides information to engineers and food scientists on the use of terpenes as an alternative solvent. In particular, the potential for ultrafiltration to be used in degumming of canola oil/terpene mixture is assessed. Our research shows that polymeric membranes are unlikely to be useful at scale in this application, as they are not readily cleaned for reuse. Conversely, a ceramic membrane of 5 kDa pore size provides the necessary rejection of phospholipids. There is some oil retention, that might require a downstream recovery step. The best results were obtained with cymene, suggesting this is a good target for industrial use.     

On the use of ultrafiltration for the concentration and desalting of phosvitin from egg yolk protein concentrate

An ultrafiltration‐based approach was integrated in the preparation of phosvitin (PVs) from delipidated egg yolk proteins. An attempt was made to concentrate PVs as well as to desalt by means of the diafiltration technique. Primary experiments were devoted to optimise the ultrafiltration performance as function of parameters such as the effects of pH, feed concentration and transmembrane pressure on permeate flux with the 10‐kDa molecular weight cut‐off (MWCO) polyethersulfone membrane at laboratory scale. Higher permeate flux values were observed at low concentration and at alkaline pH, whatever transmembrane pressure studied. Then, desalting of PVs was carried out at 50 °C with 10‐ and 30‐kDa MWCO membranes. The results showed that desalting of PVs was obtained with both the 10‐ and 30‐kDa MWCO membranes and with a few loss of protein in the permeate side.     

Ultrafiltration of Banana (Musa acuminata) Juice Using Hollow Fibers for Enhanced Shelf Life

Banana juice was clarified by cross flow ultrafiltration using a hollow fiber module under total recycle mode. Three surface-modified polysulfone-based membrane cartridges with molecular weight cut-offs 10, 27, and 44 kDa were used to identify the most suitable membrane. The effects of operating conditions—namely, transmembrane pressure drop and cross flow rate on the permeate flux and permeate quality, have been investigated. The quality of the clarified juice was evaluated in terms of viscosity, clarity, color, alcohol insoluble solids, total soluble sugar, pH, protein, and polyphenol content. The results showed that the membrane of molecular weight cut-off 27 kDa was suitable. The permeate flux depended strongly on the transmembrane pressure drop, but its variation on cross flow rate was insignificant. The clarified juice had high clarity and no pectineous materials (in terms of alcohol insoluble solids). It contained significant amount of polyphenol and protein. The storage study indicated that the juice could be successfully stored for 1 month without any additive and preservative, keeping its natural nutritional qualities, taste, and flavor intact.     

Cross-flow filtration of pectic substances during the enzymatic treatment of mandarin segment membranes

 This study is concerned with the cross-flow filtration of pectic substances, produced by the enzymatic treatment of membranes of mandarin segments, using several filtration membranes with pore sizes of between 0.45 μm and 30 kDa. Pectic substances solubilised in the digestion medium were polymers with an average molecular weight of 90–100 kDa. Pectin was retained by the membrane with a 100-kDa pore size. As a result of the addition of enzymes, pectin was degraded to a mixture of galacturonic acid and galacturonic acid oligomers, which appeared to be distributed between the retentate and the permeate. The final filtration rate of galacturonic acid oligomers was close to 100% when enzymes were present at the filtration membranes. In the absence of enzymes, the filtration rate ranged from 5% to 15%, and the permeation flux tended to decrease. The enzymatic treatment had an important effect on the resistances of the filtration membranes, and also caused a decrease in viscosity. These two factors were responsible for the increase in the permeate flux after the addition of enzymes, where this flux was almost as high as when filtration commenced. Received: 27 October 1997     

Carotenoids Concentration of Gac (Momordica cochinchinensis Spreng.) Fruit Oil Using Cross‐Flow Filtration Technology

Gac (Momordica cochinchinensis Spreng.) fruit, a traditional fruit in Vietnam and other countries of eastern Asia, contains an oil rich in carotenoids, especially lycopene and β‐carotene. Carotenoids in gac fruit oil were concentrated using cross‐flow filtration. In total recycle mode, effect of membrane pore size, temperature, and transmembrane pressure (TMP) on permeate flux and on retention coefficients has been exploited. Resistance of membrane, polarization concentration, and fouling were also analyzed. Optimum conditions for a high permeate flux and a good carotenoids retention are 5 nm, 2 bars, and 40 °C of membrane pore size, TMP, and temperature, respectively. In batch mode, retentate was analyzed through index of acid, phospholipids, total carotenoids content (TCC), total antioxidant activity, total soluble solids, total solid content, color measurement, and viscosity. TCC in retentate is higher 8.6 times than that in feeding oil. Lipophilic antioxidant activities increase 6.8 times, while hydrophilic antioxidant activities reduce 40%. The major part of total resistance is due to polarization (55%) while fouling and intrinsic membrane contribute about 30% and 24%, respectively.     

Ultrafiltration and reverse osmosis for clarification and concentration of fruit juices at pilot plant scale

The process of ultrafiltration of raw juices (peach, pear, apple and mandarin) through tubular polysulphone membranes (8 kDa) and finally concentrated by reverse osmosis membranes of tubular composite polyamide film (99 g/100 g NaCl rejection) with filtration area of 0.9 m² was studied. Furthermore, in order to obtain a higher permeate flow, the fluids were previously treated with commercial pectinolytic enzyme.The following parameters were analyzed: permeate flow, soluble solids, viscosity, density, pH, acidity, formol index, starch, pulp content, color and presence of pectin. The use of a pectinolytic enzyme provides increased permeate flux of approximately 40%, retaining the juice properties. The highest total soluble solids content was clarified peach juice from 12.2 °Brix concentrated up to 30.5 and 21.52 °Brix by using RO with transmembranes pressures of 4 and 2 MPa respectively.The results show a cross-flow velocity (1.8 m/s) which corresponds with Reynolds number that is on the lower border of a laminar flow and above of transition rate (2090 < Re < 2900). Also the (VCF) for mandarin (1.49), pear (1.53), apple (1.56) and peach (1.58) was obtained for RO process. The membranes used were characterized morphologically using scanning electron microscopy.     

Novel Procedure for Lager Beer Clarification and Stabilization Using Sequential Enzymatic,Centrifugal, Regenerable PVPP and Crossflow Microfiltration Processing

In this work, the crossflow microfiltration (CFMF) performance of different lots of lager beer, produced in a pilot scale at the Italian Brewing Research Centre (CERB, Perugia, Italy), was assessed in a bench-top plant, equipped with a 0.8-μm ceramic tubular membrane module, under constant crossflow velocity of 6 m s^?1, transmembrane pressure difference of 3.74 bar, temperature of ~10 °C, and periodic CO₂ backflushing. By feeding different beer samples (i.e., as such, precentrifuged (C), or pretreated with a commercial enzyme preparation to degrade the original arabinoxylans and β-glucans and then centrifuged (EC) to minimize the fouling contribution of yeast cells, aggregates, and polysaccharides), it was possible to increase the average permeation flux (expressed as mean value?±?standard deviation) from 112?±?13 to 199?±?17 or 330?±?22 L m^?2 h^?1, respectively. Only when using the EC-pretreated beer specimens, the permeate turbidity at 20 °C approached the limiting one (<0.6 EBC unit) recommended by the European Brewery Convention standards. As expected, the permeate chill haze at 0 °C was generally higher than the above haze target. By submitting EC-pretreated beer seeded with 0.5 g L^?1 of regenerable polyvinylpolypyrrolidone (PVPP) to CFMF, it was possible to reduce the initial total polyphenol content by 30 % and permeate chill haze to 0.60?±?0.01 EBC unit, but the average permeation flux fell to 84?±?4 L m^?2 h^?1. By performing sequentially EC pretreatments, PVPP stabilization, cartridge filtration, and CFMF, it was possible not only to re-enhance the average permeation flux at about 230 L m^?2 h^?1 near to those achievable with DE filters, but also to obtain a chill haze-free permeate ready for aseptic packaging.     

Ultrafiltration/Reverse Osmosis Concentration of Lobster Extract

A membrane concentration system consisting of tubular polysulphone ultrafiltration (UF) and polyamide reverse osmosis (RO) was evaluated for concentrating key water soluble flavor compounds from lobster extracts. Major flavor-giving compounds in the extract were glutamic acid, glycine, arginine, uridine 5′-monophosphate (UMP), succninic acid and glucose. Factors affecting performance of the UF/RO systems, such as flow rate, feed solid level, temperature and pressure, on permeate flux and solids rejection were measured. The optimum UF conditions were 1.5% feed solid level, 15 L/min feed flow rate, 50°C feed temperature and 1 MPa log mean transmembrane pressure. The RO system retained all dissolved flavor components and its ideal operating conditions were 40°C, 2.8 MPa log mean transmembrane pressure and a flow rate of 15 L/min.     

Chicory juice clarification by membrane filtration using rotating disk module

Clarification is the first step of inulin production from chicory juice, and membrane filtration as an alternative can greatly simplify this process, increase juice yield, improve product quality, and reduce the cost and waste volume. In this study, a rotating disk module (RDM) was used to investigate the clarification of chicory juice by four micro- and ultrafiltration membranes. Compared with dead end filtration, the RDM had a much higher permeate flux and product quality. High rotating speeds produced high permeate fluxes and reduced flux decline, because of the strong back transport of foulant from fouling layer to feed solution. At high rotating speeds of 1500–2000 rpm, the permeate flux increased with membrane pore size and transmembrane pressure (TMP), while at low rotating speeds (<1000 rpm), permeate flux was independent of membrane type and TMP due to a thick deposited fouling layer as a dominant filtration resistance, while carbohydrate transmission decreased at higher TMP because of denser cake layer as an additional selective membrane. The highest carbohydrate transmission (∼98%) and desirable permeate turbidity (2.4 NTU) was obtained at a TMP of 75 kPa and a rotating speed of 2000 rpm for FSM0.45PP membrane. With the RDM, the Volume Reduction Ratio (VRR) could reach 10 with a high permeate flux (106 L m⁻² h⁻¹) in the concentration test, and permeate was still rich in carbohydrate and well clarified. Chemical cleaning with 0.5% P3-ultrasil 10 detergent solution was able to recover 90% water flux of fouled membrane.     

Separation of Sucrose and Reducing Sugar in Cane Molasses by Nanofiltration

Recovery of sugars from cane molasses is a promising approach to increase the added value of molasses and reduce its environmental pollution. In this work, for the first time, nanofiltration (NF) was used for the separation of sucrose and reducing sugar in cane molasses by a cascade diafiltration-concentration process. The retention difference between sucrose and reducing sugar by all the tested NF membranes was not distinct at 25 °C, while due to the thermal-induced pore size change and enhanced solute diffusivity, the NF retention behavior changed significantly at 60 °C, and the DL membrane with a sucrose retention of 96% and a reducing sugar retention 5% was selected for the process optimization and modeling. High temperature (55–60 °C), low permeate flux (below 15 Lm^?2 h^?1), and high sugar concentration resulted in a low retention of reducing sugar due to the dominant diffusive mass transfer, which was desirable for the molasses separation by NF. Mathematical modeling could well predict the diafiltration and concentration processes if using right sugar retention data. The deviations between prediction lines and experimental data in the cross-flow filtration of real solution were mainly caused by the permeate flux variation rather than membrane fouling. After diafiltration, the ratio of sucrose in total molasses sugar increased from 76.1 to 87.9%, while in the permeate of the second concentration step, the ratio of sucrose was only 2.4%. Thus, the retentate of diafiltration could be directly used for sucrose crystallization to avoid the accumulation of reducing sugar and salts, and the permeate of the second concentration step could be concentrated by NF270 at room temperature to produce syrup drinking.