Study of different fouling mechanisms during membrane clarification of red plum juice

In this study, the flux decline mechanisms were identified during membrane clarification of red plum juice at several processing parameters, including pore size, membrane type, transmembrane pressure, temperature and velocity. The results were used to investigate the effect of changes in operating conditions on the intensity of membrane fouling. Also, scanning electron microscopy (SEM) was used for analysing fouling‐layer morphology. These results showed that the main mechanism responsible for membrane fouling was cake formation (over 95% fitness) occurring in the first stage of the process. Intermediate, standard and complete blockings were formed during most of the runs as filtration proceeded. The results also indicated that increasing the temperature from 30 to 40 °C was the most effective factor in decreasing cake‐layer fouling, reducing it by about 66.7%. Furthermore, an increase in processing velocity of up to 0.5 m s^?1 had the greatest effect on intermediate blocking, reducing it by about 86.1%. Also, increasing pressure up to 2.9 bar completely eliminated standard blocking and complete blocking. Finally, microstructure analysis of membrane using SEM confirmed that cake formation had the greatest impact on membrane fouling.     

Rotating Disk-Assisted Cross-Flow Ultrafiltration of Sugar Beet Juice

Rotating disk module (RDM)-assisted cross-flow ultrafiltration of sugar beet juice, obtained by cold pulsed electric field-assisted pressing, was studied in full recycling and concentration modes. Results of trans-membrane pressure (TMP) stepping tests with 10- and 50-kDa membranes showed that filtration flux increased with rotation speed and TMP until 1000 rpm and 4 bar. A slight variation of filtration purity was observed for a rotation speed range of 0–2500 rpm. A TMP increase resulted in purity reduction due to the formation of thicker fouling layer. A full recycling test study with a 10-kDa membrane confirmed the influence of TMP and rotation speed on filtration flux. A rotation speed of 1000 rpm and a TMP of 4 bar were selected for sugar beet juice purification, by concentrating juice from 13 to 1 L. The results of concentration mode tests revealed that, with a 10-kDa membrane, the filtrate purity could reach 95.6 ± 0.5 %, which was comparable to the purity of sugar beet juice purified by conventional liming-carbonation method. The flux decline in cross-flow filtration was still important, justifying more effective anti-fouling technologies investigation.     

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.     

Influence of operating conditions on membrane fouling in crossflow microfiltration of particulate suspensions

The effects of the operating conditions on the crossflow microfiltration (CFMF) of particulate suspensions were investigated. Lactalbumin particles were used as the feed material. Experiments were carried out in constant transmembrane pressure (TMP) mode using tubular ceramic membrane modules. All important parameters (internal and surface fouling, cake mass, height, porosity, and particle size distribution (PSD)) were estimated to provide a more complete understanding of the process than has been attempted before. Lactalbumin particles which are highly irregular in shape and widely size distributed formed an adhesive cake on the membrane surface during CFMF. The porosity and particle size of the deposited cake decreased with time of filtration. The value 100 kPa was found to be optimum with respect to the permeate flux in the studied range of TMP. Particle size classification effects of TMP and crossflow velocity (CFV) were demonstrated. The results of this study provided a possible explanation to the contradictory reports on the effect of CFV on the steady-state flux and the time required to obtain it. Significantly, the internal fouling first decreased with increasing CFV and then increased above 1.5 m s⁻¹. This is attributed to the particles size classification effect of CFV. A process was developed based on the observed effects of the operating parameters on the CFMF performance that enables operation at very low internal fouling and high flux for as long as 160 min. The developed process has the potential to become commercial if coupled with backflushing.     

Fundamental Understanding of Fouling Mechanisms During Microfiltration of Bitter Gourd (<Emphasis Type="Italic">Momordica charantia</Emphasis>) Extract and Their Dependence on Operating Conditions

Microfiltration of bitter gourd (Momordica charantia) extract using hollow fiber membrane module was carried out in the present study. To identify the dominant fouling mechanism, flux decline behavior was examined using Field model. At lower transmembrane pressure, pore blocking mechanism was found to be more important, while cake filtration was dominant at higher pressure. Higher cross flow rate reduced filtration constant indicating slower rate of membrane fouling. Additionally, surface and particle size analyses were undertaken to validate the findings of modeling. Scanning electron microscope analysis clearly showed prevalence of pore blocking mechanism at lower transmembrane pressure drop, whereas cake filtration was dominant fouling mechanism at higher pressure. Fourier transform infrared spectroscopy analysis supported the role of cake layer as a secondary membrane retaining some amount of polyphenols. Analysis of flux decline ratio also confirmed that for transmembrane pressure of 104 kPa and beyond, cake layer became compact, and hence, increase in cross flow rate was unable to influence the improvement of permeate flux. The current study provides an insight into the fouling mechanism involved in scaling up of clarification of bitter gourd extract for successful processing of this medicinal herb.     

陶瓷膜和有机膜超滤处理荔枝汁和膜垢分析及荔枝汁品质研究

应用陶瓷膜和有机膜对荔枝汁进行澄清实验,并进行采用总循环模式(TRM)研究跨膜压力(TMP)和循环流量(Qf)对膜通量(Qp)的影响,确定其各自的最优水平;采用批处理模式(TBM)研究这两个参数最优水平的组合工艺。澄清工艺中：无机陶瓷膜效果优于有机聚醚砜膜,最佳工艺条件为陶瓷膜组件、TMP 0.3MPa、Qf 40L/min。研究在TBM下,膜垢的形成原因,对微分方程--＝k(J－Jlim)J2－n进行拟合,拟合R2为无机膜0.8812和0.8478;有机膜为0.9048,并分析膜垢的形成的模式：有机膜的膜垢主要是层垢(n＝0),无机膜的膜垢形成主要是层垢和部分并在膜垢的综合情况(n＝0,n＝1)。并研究TBM模式下,总糖、总果胶、总蛋白、抗氧化活性等影响果汁品质的物质的动态过程,结果表明：在P＜0.05,无机膜在品质的保持比如总糖、抗氧化活性、总酚的截留滤等方面强于有机膜,其余的品质无显著差异。     

Evaluation of the fouling phenomenon in the membrane clarification of black mulberry juice

Mixed cellulose ester (MCE) flat membranes were used to clarify black mulberry juice, the yield of which was limited by fouling. The effects of membrane pore size (0.025, 0.1 and 0.22 μm), transmembrane pressure (0.5, 1, 1.5 and 200 kPa), and cross‐flow velocity (0.1, 0.2, 0.3 and 0.4 m s^?1) on membrane fouling were evaluated; the results showed that fouling increased with increased pore size and pressure, and decreased with increased velocity. Analysis of different resistances showed that both reversible and irreversible fouling resistances have an important role in fouling‐resistance changes. There is no cake resistance in all processes. Microstructure analysis of membrane using scanning electron microscopy confirmed the theory that intermediate blocking was the dominant fouling mechanism in MCE 0.025 μm, and standard blocking was the dominant mechanism in MCE 0.1 and 0.22 μm.     

Fouling Analysis and Performance of Tubular Ultrafiltration on Pretreated Olive Mill Waste Water

This study deals with the performance of a tubular ultrafiltration system on sieved and centrifuged olive mill waste water. A generalized statistical model was developed describing the impact and the relative importance of major experimental parameters (membrane pore size, transmembrane pressure, feed flow rate, and feed temperature) on permeate flux. According to this model, process pressure appeared to have the largest impact on permeate flux, followed by process temperature. As membrane treatment of such a difficult material largely depends on fouling, a systematic analysis of prevailing fouling mechanisms was also run. Despite sieving and centrifugation of the original waste, membrane fouling caused a flux decline of 60–65% within 15–20 min. Internal fouling, pore blocking, and cake layer formation were all responsible for membrane fouling during the first 40 min of operation. After that period, cake formation appeared to play a predominant role. Based on the proposed generalized model, the relative importance of process parameters can be evaluated and process performance can be improved by proper interventions. Independent of membrane size, fouling is a serious problem to be resolved. The qualitative performance of this process, including chemical oxygen demand distribution, polyphenol profile, and antioxidant capacity, is discussed in a separate paper.     

Recovery of bioactive compounds in kiwifruit juice by ultrafiltration

Food quality is not only a function of nutritional values but also of the presence of bioactive compounds exerting a positive effects on human health.This research was undertaken to study the influence of the ultrafiltration (UF) on the composition of some bioactive compounds of the kiwifruit juice in order to develop a natural product which can be used to fortify foods and beverages. At the same time the effect of transmembrane pressure (TMP) and temperature on the permeate flux was also investigated in order to identify the optimal operating conditions for the processing of the juice. An optimal TMP value occurred at 0.6–0.65 bar in different conditions of cross flow velocities. Steady-state permeate fluxes increased linearly with temperature in the range 20–30 °C.The kiwifruit juice was clarified in optimal operating conditions, according to the batch concentration mode, up to a final volume reduction factor (VRF) of 2.76.The analyses of flux decay according to fouling models reported in the literature revealed that the formation of a cake layer covering the entire surface of the membrane is the main cause of the membrane fouling.Most bioactive compounds of the depectinised kiwifruit juice were recovered in the clarified fraction of the UF process. The rejection of the UF membrane towards total phenolics was 13.5%. The recovery of glutamic, folic, ascorbic and citric acids, in the clarified juice, with respect to the initial feed, was dependent on the final VRF of the UF process: an increase of the VRF determines an increase of these compounds in the clarified juice. The rejections of the UF membrane towards these compounds were in the range 0–4.3%.

Industrial relevance

Among different substances contained in the kiwifruit a primary role, in the safeguard of the human health, is carried out by some bioactive compounds such as ascorbic, folic, citric, glutamic acids and polyphenols.This research was undertaken to study the influence of ultrafiltration on the composition of these compounds in order to develop a natural product which can be used to fortify foods and beverages.     

Ultrafiltration for recovery of rice protein: Fouling analysis and technical assessment

This research focused on the rice protein recovery from rice starch production wastewater by ultrafiltration. The effect of operating pressure was performed at different feed pressure from 2 to 10 bar. The suitable condition was chosen based on permeate flux; retention of protein, carbohydrate, reducing sugar, total dissolved solids (TDS); and purity of protein. The operating pressure of 6 and 8 bar was selected to conduct the study of batch operation mode with recycling of retentate. The permeate flux was highest at 6 bar, while the recovery yield and purity of protein reached a peak at 8 bar.Hermia's models were applied to analyze the fouling mechanisms in ultrafiltration (UF) of rice protein. Cake layer formation and intermediate blocking were found to occur during the UF depending on the operating pressure. The model developed in fouling analysis was used to estimate the change in component content in rice protein refinery. As result, the excellent agreement between the experimental and the model-simulated values for the solute concentrations in feed at various times of the UF operation was observed. Results indicate that UF is a potential technique for recovering rice protein.     

Ultrafiltration fouling of amylose solution: Behavior, characterization and mechanism

Applications of ultrafiltration membrane often deal with feed streams containing amylose starch. This paper describes a detailed investigation of amylose fouling during ultrafiltration. Commercial membranes made of polysulfone and fluoro polymer were used. Both adsorptive and ultrafiltration fouling were investigated. Experiments using different membrane characteristics, feed concentrations and trans-membrane pressures were carried out. The resulting fouling was characterized by water flux and contact angle measurements and was visualized by scanning electron microscopy (SEM). The results suggest that solute adsorption has occurred as noticed by significant water flux reductions as well as changes in membrane characteristics. Further, both reversible and irreversible fouling have occurred during ultrafiltration with irreversible fouling was more dominant. Apparently, cake layer formation initiated by either adsorption due to hydrophobic–hydrophobic interactions or pore blocking is the dominant fouling mechanism. However, pore narrowing instead of pore blocking was also observed for the membrane having large and relative uniform pore structure or for the ultrafiltration using low trans-membrane pressure or low solute concentration. Membrane autopsy using SEM confirmed the formation of solute layer on the membrane surface.     

ANALYSIS OF THE FOULING MECHANISM IN MICROFILTRATION OF ORANGE JUICE

The purpose of this work is theoretical and experimental evaluation of fouling effects on flux performance in clarification of freshly squeezed orange juice by cross-flow microfiltration. To identify optimum operating conditions to minimize fouling effects, juice was microfiltered on a laboratory scale plant varying axial velocity and transmembrane pressure difference. The observed flux decay was modeled using a modified form of the differential equation used to describe classical dead-end filtration processes. The mechanism of fouling during cross-flow microfiltration was identified by estimation of the model parameters according to a nonlinear regression optimization procedure. Analysis of the results revealed that the separation process is controlled by a cake filtration fouling mechanism as the juice is fed at relatively low velocity (i.e., Re = 5000) and the system is operated at low transmembrane pressure difference. In these operating conditions the permeate flux decays within the first 20–30 min to gradually achieve a limit value. At higher Reynolds number (Re = 15,000), an increase in applied transmembrane pressure (i.e., from 0.3 to 1 bar) allows the limit permeate flux to increase by a factor of about 4. In these conditions the filtration process is controlled by a complete pore blocking fouling mechanism, and the permeate flux becomes approximately invariant with respect to time, and a negligible decay may be observed. Evaluation of specific energy consumption involved in the filtration process is reported.     

Effects of palm oil-based fatty acids on fouling of ultrafiltration membranes during the clarification of glycerin-rich solution

Ultrafiltration (UF) is an alternative option that can be used to clarify glycerin-rich solutions in the oleochemical industry. However, the UF membranes used in the process were observed to have been seriously fouled in our preliminary study. Thus, the ultrafiltration of a glycerol-water-fatty acid mixture was carried out to investigate the membrane binding properties of the components and their contributions to membrane fouling. Palmitic, stearic, and oleic acid were used as fouling substances in the glycerol-water mixture. The flux decline experiments were carried out using polyvinylidenefluoride (PVDF) as well as polyethersulphone (PES) membranes with a MWCO of 30 and 25 kDa, respectively at specific conditions (T = 40 °C; ΔP = 2 bar). It was found that the PES membrane exhibited severe fouling for all types of fatty acids in solution with glycerol-water. As the pH decreased to acidic conditions, the PES membrane tended to exhibit more severe fouling than the PVDF membrane.     

Effect of l-lysine on the physicochemical properties of pork sausage

Effects of l-lysine on physicochemical properties of pork sausage were investigated. WHC values significantly increased using 0.8% l-lysine, but significantly decreased at 0.4% l-lysine (p<0.05), compared with controls. l-Lysine increased pH values and a* values, but significantly decreased CL, cohesiveness, L* values, and b* values (p<0.05), compared with controls. Addition of 0.4% l-lysine significantly (p<0.05) increased hardness, springiness, and chewiness values, compared with controls. SEM analysis showed that addition of 0.8% l-lysine induced formation of a smoother, more compact, and more uniform gel matrix, compared with controls. DSC analysis indicated that addition of 0.8% l-lysine significantly (p<0.05) increased thermal transition temperatures and enthalphy values, compared with controls, showing that interactions between l-lysine and myofibrillar proteins affected the properties of pork sausages.     

Cold atmospheric pressure plasma treatment of ready-to-eat meat: inactivation of Listeria innocua and changes in product quality

The application of cold atmospheric pressure plasma for decontamination of a sliced ready-to-eat (RTE) meat product (bresaola) inoculated with Listeria innocua was investigated. Inoculated samples were treated at 15.5, 31, and 62 W for 2–60 s inside sealed linear-low-density-polyethylene bags containing 30% oxygen and 70% argon. Treatments resulted in a reduction of L. innocua ranging from 0.8 ± 0.4 to 1.6 ± 0.5 log cfu/g with no significant effects of time and intensity while multiple treatments at 15.5 and 62 W of 20 s with a 10 min interval increased reduction of L. innocua with increasing number of treatments. Concentrations of thiobarbituric acid reactive substances (TBARS) increased with power, treatments and storage time and were significantly higher than those of control samples after 1 and 14 days of storage at 5 °C. However, the levels were low (from 0.1 to 0.4 mg/kg) and beneath the sensory threshold level. Surface colour changes included loss of redness of ∼40% and 70% after 1 and 14 days of storage, respectively, regardless of plasma treatment. The results indicate that plasma may be applicable in surface decontamination of pre-packed RTE food products. However, oxidation may constitute an issue in some products.     

Analysis of the fouling mechanisms during cross-flow ultrafiltration of apple juice

The purpose of this work was to study the fouling mechanisms of a Carbosep^® M8 membrane during the cross-flow ultrafiltration of apple juice. A new fouling model has been developed that simultaneously considers membrane blocking within the pores, at the pore mouths and by cake formation at the membrane surface. Membrane fouling by apple juice was due to internal pore blocking as well as cake formation. When operating ultrafiltration at a transmembrane pressure of 150 kPa and a cross-flow velocity of 7 m/s, fouling was minimal with a gradual decrease of the relative contribution of cake formation; however, transmembrane pressure still exceeds critical pressure. The fouling model predicts no cake formation at a cross-flow velocity of 7.4 m/s and a transmembrane pressure of 150 kPa or at a cross-flow velocity of 7.0 m/s and a transmembrane pressure of 120 kPa. Under these conditions, internal membrane blocking would be the only mechanism responsible for the decrease of permeate flux.     

Influence of feed properties on membrane fouling in crossflow microfiltration of particulate suspensions

The effects of the feed concentration (C_feed) and particle size distribution (PSD) on the crossflow microfiltration (CFMF) of suspensions containing lactalbumin particles were investigated. Experiments were carried out in constant transmembrane pressure (TMP) mode using tubular ceramic membrane modules. All the important parameters: permeate flux, internal and surface fouling, cake mass, height, porosity, and PSD were estimated. The steady-state flux (J_ss) decreased, and internal as well surface fouling and cake mass and height all increased with an increase in C_feed from 0.65 to 2.5 gL⁻¹. This was due to the availability of more particles to foul the membrane at higher C_feed. However, above 2.5 gL⁻¹ there was no significant effect of C_feed on any of these parameters. The overall observed behaviour is attributed to steady-state membrane fouling resulting from the availability of sufficient particles for maximum possible deposition under the experimental conditions reached at 2.5 gL⁻¹. The larger the feed particles, the higher was the J_ss. However, the cake mass, height and porosity were not affected by the feed PSD. Significantly, addition of larger feed particles at the steady state increased the flux by about 6%. This behaviour is attributed to the scouring effect of the large particles on the cake surface. There is scope for looking at the possibility of using the scouring effect of large particles to improve the CFMF process performance.     

The effects of various disinfectants againstListeria monocytogeneson fresh-cut vegetables

Demand for fresh, healthier convenience-type foods has stimulated sales of fresh-cut vegetables in North America. As part of an overall program to better define the microbiological safety of these products, studies were done to examine the effects of various disinfectants againstListeria monocytogeneson fresh-cut vegetables. Some of the more established disinfectants such as chlorine and chlorine dioxide, as well as some of the newer ones including Salmide^Rand trisodium phosphate were tested againstL. monocytogeneson lettuce and cabbage. Different exposure times, as well as concentrations of the disinfectants were evaluated. In addition, organic acids such as lactic and acetic were examined for their ability to inactivateL. monocytogenespresent on the surface of vegetables. Chlorine was also tested in combination with the organic acids and various surfactants. For chlorine (200ppm, 10min), the maximum observed log₁₀reduction ofL. monocytogenesat 4 and 22°C, respectively, was 1.3 and 1.7 for lettuce and 0.9 and 1.2 for cabbage. Chlorine dioxide treatment (5ppm, 10min) of lettuce and cabbage at 4 and 22°C, respectively, resulted in a maximum observed log₁₀reduction ofL. monocytogenesof 1.1 and 0.8 for lettuce and 0.4 and 0.8 for cabbage. In comparison, the highest levels of Salmide^Rused on cabbage and lettuce (200ppm) at 22°C led to maximum reductions of 1.8 and 0.6 logs, respectively. None of the surfactants tested improved the disinfectant efficiency of chlorine, and actually proved to be antagonistic. Trisodium phosphate had almost no effect on reducing numbers ofL. monocytogenes, at levels that did not affect the organoleptic quality of lettuce. Lactic acid proved to be more effective than acetic acid in reducing numbers ofL. monocytogenes, although maximum reductions of only 0.5 and 0.2 logs were observed after a 10min exposure to 1% solutions of each organic acid. In general, therefore, one can expect approximately a 1log reduction in numbers ofL. monocytogenes, regardless of the disinfectant used.     

Fouling Behavior of Polyphenols during Model Juice Ultrafiltration: Effect of Membrane Properties

Fruit juice is a complex mixture, in which polyphenols are active compounds for human health. In this paper, the effects of membrane properties, such as materials and molecular weight cutoff (MWCO), on fouling behavior of four typical polyphenols in model fruit juice ultrafiltration process were investigated. Zeta potential, contact angle, SEM image, and fouling resistances were determined. Static adsorption and rejection content of polyphenols on membranes were measured. Quantitative structure-activity relationship (QSAR) model has been developed to demonstrate the relationships between rejection and molecular parameters. Results showed that materials, MWCOs, hydrophobic properties, electrical parameters, and molecular parameters are critical factors. Membranes which were hydrophobic and positively charged have higher permeate flux and lower fouling resistance. Polyphenols were adsorbed by membranes as irreversible fouling and also had an important contribution in cake layer fouling. Retention of polyphenols on polyethersulfon 5-kDa membrane was the largest, while that on PVDF 50-kDa membrane was the least. According to QSAR analysis, rejections of polyphenols were higher when the molecules have smaller dipole moment, larger connectivity index ³X_p^v, and smaller ⁴X_pc^v.     

Effects of pretreatment and various operating parameters on permeate flux and quality during ultrafiltration of apple juice

The central composite design with a quadratic model was used to investigate the effect of temperature (20–40 °C) and transmembrane pressure (TMP) (100–300 kPa) as well as pretreatment with gelatin and bentonite (0:0–300:1500 mg L^?1) on permeate flux and fouling resistance during ultrafiltration of apple juice. The changes in some physicochemical properties were also investigated. Pretreatment of apple juice with gelatin and bentonite and an increase in the temperature and TMP significantly improved the permeate flux. In general, physicochemical properties of apple juice other than polyphenolics were not affected by the applied parameters. Using 150 mg L^?1 of gelatin and 750 mg L^?1 of bentonite for fining significantly reduced the total phenolic content and so did the fouling resistance. Fouling resistance also decreased with increasing temperature, and increasing pressure increased the fouling resistance.