Increasing Crossflow Velocity Research Articles

Direct Membrane Filtration (DMF) of municipal wastewater – A study on the prevention and remediation of fouling

Direct membrane filtration (DMF) has gained a lot of attention in recent years because of its potential to treat low-strength and low temperature wastewater, where biological based treatments are inefficient. However, fouling is a major concern which keeps this technique from being more widely used. The main aim of this study was to investigate membrane fouling, its mitigation approaches and the organic/nutrient retention during DMF of municipal wastewater by adjusting operational parameters and pretreating the sewage. In a laboratory-scale setup employing crossflow to mitigate fouling, both ultrafiltration and microfiltration membranes were utilized. Physicochemical pre-treatment of sewage with polyaluminum chloride and polyamide significantly inhibited membrane fouling and improved organics/nutrient retention. Subsequent experiments with physiochemically pre-treated sewage, using microfiltration and ultrafiltration separately, revealed that (i) an increase in crossflow velocity from 1 to 2 m s −1 improved filtration performance by reducing irreversible fouling, (ii) elevating transmembrane pressure from 0.18 to 0.4 bar increased both reversible and irreversible fouling, and (iii) periodic relaxation increased the extent of irreversible fouling, contributing to higher overall fouling in ultrafiltration. When employing DMF for sewage concentration, ultrafiltration demonstrated superior filtration performance and organics retention compared to microfiltration. Furthermore, through pre-precipitation and microsieving (100 μm) followed by DMF with ultrafiltration membranes, a remarkable removal efficiency of 92 % for chemical oxygen demand (COD), 98 % for total phosphorus (TP), and 100 % for total suspended solids (TSS) was achieved. By cleaning the fouled membranes using an alkaline cleaning solution (Ultrasil-10) at 50 °C, combined with a crossflow of 1 m s−1, the permeability was completely restored. Overall, this study demonstrates that by optimizing operational settings and cleaning conditions, a sustainable DMF process for wastewater treatment with controlled membrane fouling and improved resource recovery can potentially be developed for upscaling. Short abstractThis study investigated the effectiveness of direct membrane filtration for municipal wastewater treatment. It was found that physicochemical pre-treatment with polyaluminum chloride and polyamide significantly reduced membrane fouling and improved nutrient retention. Ultrafiltration membranes demonstrated superior performance and nutrient retention compared to microfiltration membranes. By optimizing operational parameters and cleaning conditions, a sustainable direct membrane filtration process with controlled fouling and improved resource recovery can be developed for wastewater treatment.

Effect of wall-impingement distance on fuel adhesion characteristics of split injection spray under cross-flow condition

In direct-injection spark ignition (DISI) engines, high-pressure fuel injectors introduce fuel into the cylinder, causing the spray to come into contact with and adhere to the cylinder wall; this is known as fuel adhesion. Over time, fuel adhesion contributes to carbon deposition on the cylinder wall, which affects its thermal conductivity and consequently diminishes engine combustion efficiency. This study investigates the influence of different impingement distances and cross-flow velocities on fuel adhesion under the triple injection strategy. The fuel adhesion propagation and side-view spray are measured using refractive index matching (RIM) and Mie scattering, respectively. The findings demonstrate that high cross-flow velocity promotes the fuel adhesion shape to be elongated strips. In the early stage, the growth rate of the fuel adhesion area increases with an increase in cross-flow velocity. In the later stage, the decrease rate in the fuel adhesion area initially increases with an increase in the cross-flow velocity; however, when the critical velocity threshold (20 m/s) is exceeded, the decrease rate in the fuel adhesion area tends to stabilize. The average fuel adhesion thickness then accordingly decreases with the increase in the cross-flow velocity and impingement distance in the later stage. In addition, the cross-flow promotes the volatilization of spray and fuel adhesion, thereby decreasing the fuel adhesion mass over time. In the context of carbon neutrality, this study underscores the importance of optimizing fuel injection conditions to reduce emissions and fuel consumption.

Effect of pressure and cross-flow velocity on membrane behaviour in red wine nanofiltration

Nanofiltration has found numerous applications in winemaking industry as an effective separation technology, allowing for the recovery and concentration of valuable bioactive compounds from wine/grape by-products, as well as for wine dealcoholization. However, the assessment of membrane fouling remains essential for a stable and sustainable membrane operation. Because of its complex nature, wine components (colloids and solutes such as polysaccharides, polyphenols, proteins) contribute to different mechanisms of fouling. The increase of fouling propensity as well as the conditions that contribute to it - transmembrane pressure and cross-flow velocity – are studied in the present study. Quantitative characteristics as fouling indices are discussed. Results with red wine (Mavrud) nanofiltration are obtained using two NF membranes - Nadir® NP030 P (asymmetric polyethersulfone (PES), MWCO 500 Da) and Alfa Laval NF99HF (thin film composite polyester, MWCO 200 Da). Nanofiltration runs were carried out by a constant-pressure cross-flow filtration system MaxiMem, Prozesstechnik GmbH with a rectangular flat-sheet membrane of 215 cm2 active area.Effect of transmembrane pressure (TMP) (10 to 50 bar) and cross-flow rate (1-3 l/min) on the permeate flux are discussed in view of membrane fouling. Higher operating pressures enhance the permeate flux but may also lead to increased fouling. The two membranes show very different permeate fluxes, the ones measured with NF99HF being 10-20 times higher. Increase in cross-flow velocity improves the hydrodynamic conditions such as shear stress field close to the membrane. The expected positive effect on permeate flux is the more noticeable the more pronounced the fouling. This was shown by two polymer membranes of different molecular weight cut-off exhibiting different susceptibility to fouling.

An experimental study and mathematical quantification of buoyant turbulent flame morphology under the coupling effects of inclined surfaces and crossflows

This paper investigates the flame morphology of buoyant turbulent propane flames under the coupling effects of inclined surfaces and horizontal crossflows. Horizontal crossflows were generated by wind tunnels faced to the flame on the inclined surface. The tilt angle, length, height, and attachment length of the flame were investigated with heat release rates of 6.15–18.45 kW, crossflow velocities of 0–1.00 m/s, and slope angles of 0–40°. As the results show, the relationship between the effects of inclined surfaces and crossflows on the different flame morphology parameters is different. As the crossflow velocity increases, the flame tilt angle will increase. However, the increment rate of the flame tilt angle will be limited by the inclined surface as the crossflow velocity gradually increases. The flame length is more susceptible to the crossflow than the inclined surface under coupling effects, which decreases and then increases with increasing crossflow velocity. As the crossflow velocity and slope angle increase, the flame height decreases. Meanwhile, the flame attachment length monotonically increases. The inclined surface and crossflow have a synergistic effect on the flame height and attachment length. New global correlations for flame morphology parameters were obtained based on the wind Froude number, the dimensionless heat release rate, the propane to air density ratio, and the cosine of the slope angle. The model predictions agree well with the data from this experiment and previous research.

Clarification of Limed Sugarcane Juice by Stainless Steel Membranes and Membrane Fouling Analysis.

The performance of stainless steel membranes with pore sizes of 100 and 20 nm in clarifying limed sugarcane juice was investigated under different operating conditions. An increase in transmembrane pressure (TMP) for the 20 nm membrane from 2 to 5 bar led to an increase in the average flux from 146.6 Lm−2 h−1 to 187.8 Lm−2 h−1 (approximately 9 h). The increase in crossflow velocity from 2 to 5 m/s led to an increase in the average flux from 111.9 Lm−2 h−1 to 158.1 Lm−2 h−1. The increase in temperature from 70 °C to 90 °C caused an increase in the average flux from 132.8 Lm−2 h−1 to 148.6 Lm−2 h−1. Simultaneously, the test produced a high-quality filtered juice with an average of 1.26 units of purity rise. The purity increased with time, and a 99.99% reduction in turbidity and an average 29.3% reduction in colour were observed. In addition, four classic filtration mathematical models and scanning electron microscopy (SEM) analyses suggested that cake formation is the main mechanism for flux decline. Fourier transform infrared (FTIR) spectrometry and energy-dispersive X-ray (EDX) spectrometry indicated that organic fouling is the main foulant. This study demonstrates the potential of stainless steel membranes as filters for the clarification of raw sugarcane juice.

Separation of TiO2 particles from suspension using indigenous low-cost ceramic microfiltration membrane

The increased use of TiO2 nanoparticles in manufacturing and commercial products has led to environmental contamination and health issues. This study aimed to apply tubular ceramic membrane fabricated using low-cost clays (kaolin, quartz) along with hydroxypropyl methylcellulose binder for the separation of TiO2 nanoparticles from water. The prepared tubular ceramic membrane exhibited excellent water permeability (1.4945 × 10−7 m3/m2s kPa) with an average pore size of 0.178 μm and porosity of 40 %. Cross flow microfiltration experiments using TiO2 nanoparticles suspension were performed by varying the applied pressure (138–414 kPa), cross flow velocity (2.41 × 10−3 - 5.63 × 10−3 m/s), pH (4–11) and feed concentration (0.05–1 wt%). The permeate flux increased linearly with an increase in the pressure as well as cross flow velocity with a maximum permeate flux of 4.24 × 10−5 m3/m2s at 414 kPa, whereas a reduction in permeate flux was observed with increasing feed concentration of TiO2. The membrane displayed 100 % separation efficiency at all the investigated pressures. Furthermore, the membrane fouling mechanism during the microfiltration process was analyzed using resistance-in-series model. Results demonstrated that filtration resistance (Rf) and total resistance (Rt) decreased with increasing cross flow velocity from 2.41 × 10−3 m/s to 5.63 × 10−3 m/s, whereas filtration resistance remained constant at high pressures. The estimated membrane cost is 253 USD/m2 based on raw materials, energy consumption, manpower and equipment cost. These promising results elucidated the suitability of tubular ceramic membrane towards the removal of TiO2 from wastewater.

Flow Field and Heat Transfer of an Impinging Synthetic Jet in the Presence of Cross-Flow: Application of SAS and DES Approaches

Nowadays, synthetic jets have various applications such as cooling enhancement and active flow control. In the present paper, the capability of two turbulence modelling approaches in predicting thermal performance of an impinging synthetic jet is investigated. These two approaches are scale adaptive simulation (SAS) and detached eddy simulation (DES). Comparisons between numerical data and experimental studies reveal that the ability of DES in predicting the asymmetrical trend of heat transfer profiles is better than SAS in almost all the study cases. Although, near the stagnation zone, the performance of SAS is superior. Results show that the effects of parameters such as frequency, cross-flow velocity and suction duty cycle factor are well predicted by both approaches. An increase of cross-flow velocity from 1.81 m/s to 2.26 m/s results in an improvement of [Formula: see text] near the stagnation point by almost 16.3% and 9.2% using DES and SAS, respectively.

Improving the osmotic energy conversion efficiency of multiple nanopores by a cross flow

Osmotic energy conversion through charged nanopores is promising for next generation renewable energy. Towards practical use, applying a large-scale multi-pore system is necessary and almost inevitable. Unfortunately, due to the presence of a significant ionic concentration polarization (ICP) at a high pore density, the power generated per pore is usually much less than that generated from a single pore. To alleviate this problem, we propose applying a cross flow parallel to the pore openings. This lowers the degree of ICP, thereby improving its osmotic power generation performance. Several ways of applying the cross flow are examined, and the results of numerical simulation reveal that applying it on the lower salt concentration side only can yield the best performance. In this case, the osmotic power generated increases with the increased cross flow velocity. In addition to assessing the performance under various conditions, the mechanisms associated with the system under consideration are discussed.

A two-dimensional numerical study of film boiling over an elliptical cylinder in the mixed regime under aiding and orthogonal saturated liquid flow configurations

Abstract

Microbubble generation with shear flow on large-area membrane for fine particle flotation

Fine particle flotation is carried out in a flotation column with a 19-channel ceramic membrane sparger. The microbubble generation is controlled by the shear flow in the membrane channels. Bubbles in the flotation column are photographed via a high speed video camera. Gas holdup and quartz recovery is investigated under different operating conditions. Gas holdup in the flotation column firstly increases and then decreases with the increase in superficial gas velocity. Similar trend in gas holdup is also found by increasing cross flow velocity. Larger particle concentration in the feed results in smaller gas holdup, while the gas holdup positively changes with collector concentration. The quartz recovery is strongly influenced by gas holdup and bubble size. Similarly, the recovery firstly increases and then decreases when increasing superficial gas velocity and cross flow velocity. The collector concentration plays a more obvious role in flotation recovery at high superficial gas velocity.

Saturated film boiling over a circular cylinder subjected to horizontal cross-flow in the mixed regime

Film boiling over a circular cylinder in a horizontal cross-flow of saturated liquid is studied in the mixed regime that is characterized by a combined influence of buoyancy and flow inertia at low magnitudes of the Froude number (Fr). Liquid-vapor interface evolution and the ensuing vapor wake dynamics together with heat transfer have been determined through a computational framework developed for phase change problems on two-dimensional unstructured grids using a coupled level set and volume of fluid interface capturing method. While the quasisteady nature of ebullition cycle is gradually lost as Fr increases, the effect of cross-flow orientation with respect to gravity is shown to be nontrivial in the mixed regime. A direct consequence of the orthogonal gravity and flow fields is an anomalous impairment of heat transfer with an increase in cross-flow velocity under certain conditions, which is discussed in detail. Simultaneously, the film boiling behavior as influenced by several other hydrodynamic and thermal parameters is also ascertained. The interplay between buoyancy and inertia is further highlighted while discussing the interdependent liquid and vapor wake characteristics in the mixed regime with horizontal cross-flow. The liquid wake behavior is shown to result not only from the bluff body geometry but also the instantaneous vapor wake profiles, with the wall superheat affecting the time scale of wake interaction. Finally, a reduction factor (ξ) is proposed and determined as a function of the Froude number, which is used in conjunction with a correlation for upward cross-flow film boiling to predict the heat transfer.

Membrane fouling in a hybrid process of enhanced coagulation at high coagulant dosage and cross-flow ultrafiltration for deinking wastewater tertiary treatment

A hybrid process of enhanced coagulation at a high dosage of polyaluminum chloride and flat-sheet cross-flow ultrafiltration was used for the advanced treatment of the effluent from a biological treatment process of deinking wastewater in a paper mill. The experimental results obtained by a small-scale continuous laboratory experimental device showed that the absorption resistance was significantly lower than the membrane intrinsic resistance, the concentration polarization resistance, the pore blocking resistance, and the cake layer resistance and so it can be ignored. With increasing polyaluminum chloride dosage from 0 to 2,000 mgL-1, the total membrane filtration resistance decreased and the membrane flux increased, but the concentration polarization resistance increased. With the increase in cross flow velocity, the total membrane filtration resistance, the pore blocking resistance, the layer resistance, and the concentration polarization resistance all decreased, and consequently, the membrane flux increased. With regard to the concentration polarization resistance, the cross flow velocity had a more significant effect than the trans-membrane pressure. But the trans-membrane pressure had a more significant effect on the layer resistance, the pore blocking resistance, and the total membrane filtration resistance than the cross flow velocity. The filtration resistance at the polyaluminium chloride dosage of <1,000 mgL-1 could be ranked as follows: the membrane intrinsic resistance > the pore blocking resistance > the layer resistance > the concentration polarization resistance> the absorption resistance. But it was the membrane intrinsic resistance > the concentration polarization resistance > the pore blocking resistance > the layer resistance > the absorption resistance at the dosage of ≥1,000 mgL-1. The results are helpful for the membrane fouling control and can promote the application of flat-sheet cross-flow membrane process, resultantly improving the reclaim and reuse of deinking wastewater, and reducing the emission of contaminants in deinking wastewater.

Controlling microbubbles in alcohol solutions by using a multi‐channel ceramic membrane distributor

AbstractBACKGROUNDMicrobubbles are gaining more attention in environmental, medical, agricultural and industrial processes. Alcohol addition plays an important role in controlling microbubble generation. The effect of n‐butanol concentration on microbubble characteristics has not been studied, thus experiments have been done to investigate the control of microbubbles in alcohol solutions.RESULTSMicrobubbles were successfully generated using a 19‐channel ceramic membrane. The bubble Sauter diameter was found to decrease with increasing n‐butanol concentration. Increasing cross flow velocity and decreasing superficial gas velocity resulted in smaller bubbles. Gas holdup and specific interfacial area was found to increase with increasing n‐butanol concentration. The volumetric mass transfer coefficient Kla was found to increase with increasing n‐butanol concentration, following the trend in specific interfacial area. Increasing cross‐flow velocity and superficial gas velocity resulted in increased Kla.CONCLUSIONSBubble characteristics in solutions with different n‐butanol concentrations are very different. Alcohol addition is an important way to generate smaller bubbles and larger gas holdup. © 2018 Society of Chemical Industry

Fouling Behaviour During Cross Flow Ultrafiltration of Cassava Starch Hydrolysate Using Polyacrylonitrile Membrane

Ultrafiltration (UF) is considered as a promising alternative to the traditional clarification techniques in the sugar industries. In this work, a hollow fiber UF membrane (polyacrylonitrile, MWCO 100 kDa) was used for clarification of cassava starch hydrolysate. The influence of various operating parameters, such as transmembrane pressure (TMP), cross flow velocity and pH hydrolysate on the membrane fouling was assessed. The results showed that TMP higher than 1.0 bar was not effective to improve flux. Increasing cross flow velocity was virtually effective to reduce permeate flux decline. The steady state flux, Jssincreased significantly when pH of the feed was adjusted to alkaline condition; however, this resulted in dark brown clarified glucose syrup. Operating at natural pH of 4.5, the membrane selectivity was close to 100%. Evaluation of hydraulic resistance indicated that concentration polarization and pore blocking were beyond approximately 50 and 40% of the total filtration resistance, respectively. Moreover, scanning electron microscopy showed that extensive fouling layer was deposited on the membrane surface. Finally, the developed cleaning procedure could restore membrane performance approximately 45% of its initial performance.

Effect of Internal Crossflow Velocity on Film Cooling Effectiveness—Part II: Compound Angle Shaped Holes

In gas turbine engines, film cooling holes are commonly fed with an internal crossflow, the magnitude of which has been shown to have a notable effect on film cooling effectiveness. In Part I of this study, as well as in a few previous studies, the magnitude of internal crossflow velocity was shown to have a substantial effect on film cooling effectiveness of axial shaped holes. There is, however, almost no data available in the literature that shows how internal crossflow affects compound angle shaped film cooling holes. In Part II, film cooling effectiveness, heat transfer coefficient augmentation, and discharge coefficients were measured for a single row of compound angle shaped film cooling holes fed by internal crossflow flowing both in-line and counter to the spanwise direction of coolant injection. The crossflow-to-mainstream velocity ratio was varied from 0.2 to 0.6 and the injection velocity ratio was varied from 0.2 to 1.7. It was found that increasing the magnitude of the crossflow velocity generally caused degradation of the film cooling effectiveness, especially for in-line crossflow. An analysis of jet characteristic parameters demonstrated the importance of crossflow effects relative to the effect of varying the film cooling injection rate. Heat transfer coefficient augmentation was found to be primarily dependent on injection rate, although for in-line crossflow, increasing crossflow velocity significantly increased augmentation for certain conditions.

Dynamic membranes of powder-activated carbon for removing microbes and organic matter from seawater

A dynamic membrane was formed by introducing powder-activated carbon (PAC) prior to the cross-flow microfiltration of seawater. The microbes and organic matter in the seawater were removed efficiently through the interception, adsorption, and biodegradation of the PAC dynamic membrane. The properties of PAC dynamic membranes formed under various operating conditions were analyzed. The relationship between the specific filtration resistance of a dynamic membrane and transmembrane pressure was regressed as a power-type empirical equation for a given cross-flow velocity. An increase in cross-flow velocity led to higher specific filtration resistance because of the smaller particle size distribution. The thickness of a dynamic membrane increased with the transmembrane pressure but decreased with the cross-flow velocity. The thickness was correlated with the ratio of tangential to normal drag forces exerted on the PAC particles on the membrane surface. The filtrate quality for PAC dynamic membrane filtration was analyzed. Humic acid (HA) and turbidity were not detected. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) had maximum removals of approximately 80% and 92%, respectively. The behavior by which HA was adsorbed on a PAC conformed to the Freundlich isotherm, and the modified Wheeler equation produced appropriate estimates of the breakthrough time. The breakthrough time increased with the thickness of the dynamic membrane. This study presents a method by which the filtration performance, such as filtration flux, thickness, and breakthrough time of the dynamic membrane, can be predicted directly from operating conditions.

Effect of the high cross flow velocity on performance of a pilot-scale anaerobic membrane bioreactor for treating antibiotic solvent wastewater

The effect of high cross flow velocity (CFV) on the operational efficiency of a pilot-scale anaerobic membrane bioreactor (AnMBR) treating antibiotic solvent effluents was explored. The average of total Chemical Oxygen Demand (COD) and tetrahydrofuran (THF) removal efficiencies during four Runs were 96.5% and 98.7%. Meanwhile, biological removal contributions were 74.3% and 78%, the rest part was attributed by the physical removal process of the membrane block, VFA (Volatile Fatty Acids) and alpha value (VFA/alkalinity) increased with the increase of CFV, resulted alkalinity decreased. Biomass concentration mixed liquid suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) as well as the polysaccharide increased smoothly in the suspended sludge with the CFV increasing, and the protein content decreased gradually. However, the concentration of biomass, polysaccharide and protein presented opposite trends in the attached sludge of the membrane. The results indicated that AnMBR can effectively treat the antibiotic solvent wastewater under high CFV.

Chemically cleaning of UF membranes fouled by oily waste water.

The Ultra filtration membranes are used for treatment and reused of oily waste waters. The fouling of the ultra filtration membranes is caused due to inorganic and organic materials present in waste water that adhere to the surface and pores of the membranes and resulted in fouling and deterioration perforformance with increase in cost of energy and membranes replacement. In this experiment, Ultra filtration membranes fouling and cleaning were performed with oily waste water and selecting cleaning agents using laboratory scale cross flow membrane test unit. The result showed that the combination of cleaning agent that is metal chelating agent (Ethylene diamine tetraactetic acid) and an surfactant (sodium dodecyl sulfate (SDS) and sodium hydroxide were able to clean fouled membranes very effectively than the individual cleaning agent. The flux recovery percentage was found to improve with increasing cross flow velocity, temperature, pH and concentration of the cleaning solutions. Keywords-ultrafiltration; fouling; cleaning; surfactant; oily waste water. I. INTRODUCTION The fouling of membranes is typically caused by inorganic and organic materials that adhere to the surface and pores of the membrane and result in deterioration of performance (reduce flux of the membrane) with consequent increase in costs of energy and membrane replacement. A. Fundamental of Separation The forces of interaction between the membrane surface and particles in the solution are important in understanding the fouling phenomena. The normal basis for quantifying particle surface interaction is DLVO theory where the particle surface interactions in aqueous environments could be predicted by the summation of van der Waals and electrostatic double layer forces. Reducing the interaction between the particles and the membranes as much possible can reduce the fouling phenomena. This can be achieved when the critical value (flux and pressure) arises as a balance between the hydrodynamic force driving solute towards the pore and electrostatic forces opposing the motion. Critical flux stems from the concept that the higher the flux the stronger is the drag force towards the membranes. The stronger concentration polarization and higher the compaction of particles. Critical flux is defined as the limiting flux value below which a flux decline over time does not occur.(1).the number of parameter influenced this critical flux have been discussed in detail can be found(2).It is maintained that if one operates below the critical flux the fouling can be avoided or minimized. The fouling is common to all types of membrane separation. B. Fouling Membranes fouling are an extremely complex phenomenon that has not been defined precisely. In general the term used to describe the undesirable formation of deposits on membrane surfaces. This occurs when rejected particles are not transported from the surface of the membrane back to the bulk stream. The foul ant are typically colloidal materials of one types or another and their properties and interaction with membranes dominant fouling /cleaning processes. Colloids are defined as fine suspended particles in the size range of few nanometers to few micrometers. Examples of common colloids sizes foulant includes inorganic(clay, silica salt and metal

A threshold flux phenomenon for colloidal fouling in reverse osmosis characterized by transmembrane pressure and electrical impedance spectroscopy

The dependence of membrane fouling on flux has been investigated using silica as the model foulant in a crossflow membrane module operated at constant flux. Electrical impedance spectroscopy (EIS) was used to monitor the electrical properties of the fouling process.We show that the nature of a flowing colloidal suspension of silica on the membrane surface changes when a transition or threshold flux is reached. This transition was well-defined and was reflected in the changes of the slope of transmembrane pressure (TMP) with flux and the conductance of the diffusion polarization (DP) layer determined by EIS. The threshold flux increased with increasing crossflow velocity. The effect of a spacer in the feed channel was also investigated and the presence of spacer increased the threshold flux. The conductance of the diffusion polarization layer (GDP) derived from the low frequency region in the EIS was identified as the most important EIS parameter for signaling the onset of cake formation and the cake enhanced concentration polarization (CECP) effect. TMP measurements on their own provided limited information on these phenomena. The threshold flux was affected strongly by the crossflow velocity and this was also illustrated in the change in the minimum of the GDP with increasing flux. This study suggests that EIS could be applied “online” using a side-stream, 'canary' cell to continuously monitor a reverse osmosis system to ensure its operations remain below the threshold flux.

Effect of ceramic membrane channel diameter on limiting retentate protein concentration during skim milk microfiltration

Our objective was to determine the effect of retentate flow channel diameter (4 or 6mm) of nongraded permeability 100-nm pore size ceramic membranes operated in nonuniform transmembrane pressure mode on the limiting retentate protein concentration (LRPC) while microfiltering (MF) skim milk at a temperature of 50°C, a flux of 55kg·m−2·h−1, and an average cross-flow velocity of 7 m·s−1. At the above conditions, the retentate true protein concentration was incrementally increased from 7 to 11.5%. When temperature, flux, and average cross-flow velocity were controlled, ceramic membrane retentate flow channel diameter did not affect the LRPC. This indicates that LRPC is not a function of the Reynolds number. Computational fluid dynamics data, which indicated that both membranes had similar radial velocity profiles within their retentate flow channels, supported this finding. Membranes with 6-mm flow channels can be operated at a lower pressure decrease from membrane inlet to membrane outlet (ΔP) or at a higher cross-flow velocity, depending on which is controlled, than membranes with 4-mm flow channels. This implies that 6-mm membranes could achieve a higher LRPC than 4-mm membranes at the same ΔP due to an increase in cross-flow velocity. In theory, the higher LRPC of the 6-mm membranes could facilitate 95% serum protein removal in 2 MF stages with diafiltration between stages if no serum protein were rejected by the membrane. At the same flux, retentate protein concentration, and average cross-flow velocity, 4-mm membranes require 21% more energy to remove a given amount of permeate than 6-mm membranes, despite the lower surface area of the 6-mm membranes. Equations to predict skim milk MF retentate viscosity as a function of protein concentration and temperature are provided. Retentate viscosity, retentate recirculation pump frequency required to maintain a given cross-flow velocity at a given retentate viscosity, and retentate protein determination by mid-infrared spectrophotometry were all useful tools for monitoring the retentate protein concentration to ensure a sustainable MF process. Using 6-mm membranes instead of 4-mm membranes would be advantageous for processors who wish to reduce energy costs or maximize the protein concentration of a MF retentate.