Effect of Fouling Conditions and Cake Layer Structure on the Ultrasonic Cleaning of Ceramic Membranes

Abstract

Homogeneous alumina membranes fouled by polystyrene latex particles at different pH values and ionic strengths were subjected to ultrasonic cleaning. Cleaning was more effective at high and low pH than at neutral pH. At low pH values, less repulsive particle‐particle interactions resulted in the removal of millimeter‐scale aggregates and highly effective cleaning. At near‐neutral pH, stronger repulsive particle‐particle interactions caused detachment to occur as individual particles from the cake layer rather than as flocs, which was a slightly less effective cleaning mechanism. Ultrasonic cleaning of cake layers formed at high ionic strength (>0.3 M KCl) was less effective than cleaning at lower ionic strength (<0.3 M KCl). High ionic strength caused particles to coagulate in solution and deposit as flocs on the membrane surface forming a highly permeable fouling layer. This fouling layer was resistant to ultrasound at the sub‐optimal cleaning conditions used in this study, perhaps due to particle attachment occurring within a primary energy minimum. Membrane cleaning experiments performed with particles of varying size showed that particle size was less important than the surface potential of the particles. For a given mass, particles that possessed the largest surface potential formed the thickest fouling layer, irrespective of particle size, and showed the greatest improvement in flux with ultrasonic cleaning. These results demonstrate that solution conditions influence ultrasonic cleaning of membranes primarily by modifying particle‐particle and particle‐membrane interactions as well as cake layer structure, rather than by impacting the extent or magnitude of cavitation events.     

一体式平片膜生物反应器处理抗生素废水研究

以抗生素发酵废水为处理对象,对一体式平片膜生物反应器在运行过程中膜的性能进行了研究。研究结果表明,膜的截留作用使反应器活性污泥的质量浓度达15g/L,CODCr去除率达到86%。运用RIS阻力模型对在线海绵擦洗的效果进行了初步研究,认为在线海绵擦洗对恢复膜通量和防止各种阻力因素的累积具有积极的实践意义。     

Dynamic in-series resistance modeling and analysis of a submerged membrane bioreactor using a novel filtration mode

This study is focused on the physical filtration characteristics of a flatsheet membrane bioreactor (MBR) operated under a novel filtration mode. The objective of this research was to demonstrate the possibility of running an MBR with high MLSS concentration for prolonged periods without frequent blocking of the membranes. Current MBR designs, mostly dictated by the manufacturers, have restrictions on the level of MLSS due to fouling. It has been observed that this restraint can be eliminated by applying high shear rates for better removal of cake layer from membrane surface. A pilot scale MBR was setup at the inlet works of a domestic sewage treatment plant. The system was dynamically modeled and calibrated for flux, hydraulic permeability, transmembrane pressure using the in-series resistance model. Resistance components were experimentally determined and compared against the results of dynamic simulations. Intrinsic membrane resistance (R_m) and fouling resistance (R_f) were the major components contributing to total resistance with fractions of 69% (R_m/R_t) and 30% (R_f/R_t) respectively. It was found that cake resistance did not have major impact on the total resistance which was linked to the high aeration intensity. Proposed model was validated by experiments which indicated its potential use on other MBR systems.     

Experimental Study of the Mechanism of Constant Pressure Cake Filtration: Clogging of Filter Media

Abstract

Failure of data taken in pilot plant filtration of liquefied coal to fit conventional analysis led to research summarized in this paper. Historically, the effect of migrating fine particles in cake filtration has been ignored in theoretical treatments. In usual development, the total resistance to flow has been broken into cake resistance R_C and medium resistance R_m. Experimentors have only measured the total resistance and have assumed that R_m remained constant. In this investigation, a filter with seven probes was empolyed to measure the individual resistances. Medium resistance is found to increase with time and mass of dry cake per unit area due to migration of fine particles into the interestices of a filter medium.     

Cake filtration of suspensions in viscoelastic fluids

The fundamental framework for cake filtration of suspensions in viscoelastic media is extended to include the effects of polymer retention, including adsorption in the filter cake, polymer retention and elongational flow in the filter medium, which also undergoes compaction, and evaluation of polymer degradation in the filter cake and medium. Experimental data obtained in constant pressure filtration of starch suspensions in dilute aqueous polyacrylamide solutions confirmed the prediction of an enhanced apparent medium resistance R_ma and a reduced cake resistance α_R. Evaluations are presented of the contributions to the pressure drop due to enhanced normal stresses in elongational flow and to polymer retention (adsorption), and of the ratio of the particle size with and without adsorbed polymer in the cake. The analysis of the data points to high levels of polymer degradation during the flow of the polymer solution through the filter cake and medium.     

Filtration performance of ceramic membrane for the recovery of volatile fatty acids from liquid organic sludge

This research focused on the filtration performance of a membrane-coupled fermenter system for dissolved organics recovery from liquid organic sludge. Over the range 0.1-5 μm, the magnitude of total membrane resistance (R₁) is ranged as follows in the order: 0.1 μm>0.2 μm>0.5 μm>1 μm>2 μm>5 μm. The cake layer resistance (R_c) occupied about 68-88% of total resistance. The decline of permeation flux was mainly attributed to R_c, which was formed by a strong deposition from physicochemical interactions of solids on the membrane surface. Higher suspended solids concentration of suspension caused lower permeation flux. However, there was not a proportional relation beyond a certain SS concentration. The cross-flow velocity on the membrane surface was faster, which resulted in higher permeation flux and also more efficiency with low transmembrane pressure. The appropriate pH of suspension was in the range of 5.0 to 6.0 for dissolved organics recovery as well as permeation flux. It is possible for bacteria to be separated perfectly with 0.1 μm and 0.2 μm membrane pore sizes. Based on experimental results, optimal membrane pore size for the recovery is believed to be around 1 μm.     

Advanced reverse osmosis process with automatic sponge ball cleaning for the reclamation of municipal sewage

These experiments were conducted with secondary effluent from the terminal plant at Osaka, Japan, in order to determine the potential of the sponge ball cleaning system as an advanced reverse osmosis membrane cleaning technique. It was confirmed that sandfiltration of the feed as a method for reverse osmosis pretreatment and the use of chemical cleaning reagents to restore flux levels were unnecessary, when sponge ball cleaning was used.As a result, the product water flux was maintained at 0.65 ～ 0.75m³/m² day at 25°C and membrane rejection was more stable. No damage to the membrane, which would mean a decline of rejection ability, was recognized by scrubbing of the membrane surface by sponge rubber balls.It was confirmed that tight membranes were more suitable than loose ones because firstly it was easier to remove membrane fouling, secondly the product flux was nearly equal, and finally the product water was of better quality.     

磁絮凝膜过滤工艺中附加磁场强化清洗

基于磁强化絮凝膜过滤(MEFMF)工艺中磁絮体和含磁滤饼层的特性,设计了在线(on-line)和离线(off-line)磁强化清洗(MEC)工艺.在磁场和曝气剪切的协同作用下,含磁滤饼层脱离膜纤维表面,膜通量恢复率较常规物理清洗(RC)明显提高.在离线磁强化清洗时,设计反洗装置中心的磁感应强度为6 mT,曝气强度为500 L·m^-2·min^-1,控制清洗时间为5 min,维持反洗压力0.04 MPa,可达到最佳的膜清洗效果,通量恢复率达97%以上.在外加磁场强化清洗过程中,滤饼层中的磁种发生磁化作用,滤饼层表现出微弱的宏观磁性,在磁场的作用下向磁极运动,使得膜通量恢复率明显提高.此外,在MEFMF工艺中采用间歇磁强化清洗,可以更加有效地去除引起不可逆膜污染的胶体和有机物,降低膜污染速率,减缓膜污染.     

The influence of cake residence time on the stable operation of a high-temperature gas filter

Varying degrees of incomplete filter regeneration lead to a progressive shortening of filtration cycles, which was both measured and modeled as a function of the time interval t_c between cleaning pulses (our definition of “cake residence time”). Of particular interest was the effect of temperature. Experiments were performed with pressure-pulse cleaned ceramic filter elements typically used in high-temperature gas filtration, for up to 200 cycles, at two temperature levels (200 and 300 °C), at two filtration velocities (3 and 5 cm/s), for several values of cake thickness, and with two different particle materials. The cake residence time was varied by adjusting the initial cycle length between 6 and 87 min without changing the cake thickness.A 2-stage model is proposed to describe the observed patterns of decrease in cycle duration as a function of cycle length t_c. For cycles exceeding a certain critical length t_c*, the rate of decrease is an exponential function of (t_c-t_c*), where t_c* and the other fit parameters was found to depend mainly on particle material as well as temperature. Below t_c* the rate of decrease becomes constant and independent of the actual cycle length. The constant was found to be a weak function of flow velocity and cake thickness as long as the cake was not too thin; a temperature dependence was not discernible for Phase 2.The results support the uniform-residual-layer hypothesis as a mechanistic explanation of the filtration behavior during both phases: a thin incremental layer of cake is left behind after each regeneration pulse, which drives the loss of cycle length. During Phase 1 the incremental layer is a temperature dependent function of cake residence time (in excess of t_c*); during Phase 2 it is not. This suggests that the thickness of this residual cake layer is related to the solidification rate in the cake. For cake residence times below a critical value, the degree of solidification is too low to affect the stability. The regeneration efficiency is then controlled by other factors such as filtration velocity and regeneration intensity (cake thickness), as in any typical bag house filter.     

Skin Layer on Thermally Dried Sludge Cake

This work utilized an X-ray micro-computerized tomography scanner (micro-CT) to investigate how skin layers—hard and relatively impermeable layers that hinder mass transfer—form and develop on wastewater sludge cake with (cake-O) or without artificial cracks (cake-N). A novel scheme that applies Otsu's algorithm twice was employed to determine the solid phase and skin layers in the scanned cake images. Initial cracks in a cake had significant impact on how the skin layer would form on the cake. A unique correlation between effective surface area to drying (not covered by a skin layer) and moisture content was identified. The advancement velocities of skin layers on drying cake were evaluated.     

Effect of Hydraulic Retention Time on Sludge Properties,Cake Layer Structure,and Membrane Fouling in a Thermophilic Submerged Aerobic Membrane Bioreactor

Sludge properties, cake layer structure, and membrane fouling in a membrane bioreactor were studied under various hydraulic retention times (HRT). A decrease in HRT resulted in an increase in extracellular polymeric substance production in bulk sludge and changes in cake layer structure from gel layer to one or two cake layers. Particle size distribution in cake sludge changed with respect to HRT. An evolution in cake layer thickness and porosity was observed with trans-membrane pressure (TMP) jump. The change in cake layer structure might bear more responsibility for the TMP jump than the quantity of cake layer.     

Skin Layer on Thermally Dried Sludge Cake

This work utilized an X-ray micro-computerized tomography scanner (micro-CT) to investigate how skin layers—hard and relatively impermeable layers that hinder mass transfer—form and develop on wastewater sludge cake with (cake-O) or without artificial cracks (cake-N). A novel scheme that applies Otsu's algorithm twice was employed to determine the solid phase and skin layers in the scanned cake images. Initial cracks in a cake had significant impact on how the skin layer would form on the cake. A unique correlation between effective surface area to drying (not covered by a skin layer) and moisture content was identified. The advancement velocities of skin layers on drying cake were evaluated.     

Development of new hybrid ultrafiltration membranes by entanglement of macromolecular PPSU‐SO3H chains: Preparation,morphologies, mechanical strength,and fouling resistant properties

The present work focuses on the preparation of Polyphenylsulfone (PPSU) membranes with enhanced antifouling surfaces through an incorporation of sulfonated Polyphenylsulfone (PPSU‐SO₃H), which acts as both, surface modifying agent and macromolecular additive. Initially, Sulfonated polyphenylsulfone (PPSU‐SO₃H) was synthesized by using chlosulfonic acid via bulk modification method. The degree of sulfonation (DS, %) of PPSU‐SO₃H was calculated by using NMR (nuclear magnetic resonance).The phase inversion technique was used to prepare all asymmetric membranes by allowing the PPSU‐SO₃H (different wt %) to entangle with the PPSU membrane matrix. All prepared membranes were characterized by using scanning electron microscope (SEM), X‐ray diffraction analysis (XRD), contact angle analysis (CA), mechanical strength analysis, molecular weight cut off (MWCO), porosity (%), mean pore size, and BSA adsorption studies. The performance efficiency of the membranes was evaluated by using BSA protein as a model foulant in terms of permeability, rejection (SR %), R_m (hydraulic resistance), R_c (cake layer resistance), R_p (pore plugging resistance), R_r (reversible fouling), R_ir (irreversible fouling), and FRR (flux recovery ratio). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41986.     

Crossflow Microfiltration-Fouling Mechanisms Studies

Abstract

Our objective has been to improve the commercial potential of a crossflow microfiltration process with lime softening of surface waters rich in humic and fulvic acids. These components complicate the filtration of CaCO₃ solids both in the filter cake layer and through direct interactions with the nylon membrane support surface. We characterized the humic/fulvic acid fouling and developed several strategies for alleviating the problem. Physical cleaning methods like crossflow and backflush alone are ineffective. We devised chemical pretreatment and chemical cleaning procedures which improve performance.     

Ultrafiltration of Humic Acid Solution: Effects of Self‐dispersible Carbon Black and Cations

Abstract

Effects of carbon black (CB) addition on membrane fouling and rejection of macromolecular humic acids (HA) were evaluated by a stirred‐cell ultrafiltration unit. Stable CB dispersions increased filtration resistances, but enhanced HA rejection by the membranes. Monovalent and divalent ions affected the filtration resistance of CB solution differently; namely, NaCl solution showed a very high resistance due to the concentration of CB in the diffusion boundary layer near the membrane surface, whereas CaCl₂ and MgCl₂ solutions showed only cake resistance. The cake layer containing both CB and HA was more easily removed from the membranes than HA‐cake layer.     

Ultrafiltration of W/CO2 Microemulsions in Ceramic Membranes

Abstract

Water‐in‐CO₂ (W/CO₂) reverse microemulsions stabilized with 1100 Da poly(ethylene glycol)‐poly(propylene glycol)‐poly(ethylene glycol) block copolymer were recovered using an ultrafiltration ceramic membrane in a custom high‐pressure cross‐flow separation unit. Viscosity‐corrected liquid CO₂ flux (298 K) through the membrane was investigated as a function of time and surfactant concentration to determine the cake layer mass transfer resistance. Rapid CO₂ flux decline was observed with increasing surfactant concentration, denoting cake layer buildup on the membrane surface. For instance, at 0.09 and 0.55 wt% surfactant, the ratio of cake resistance to membrane resistance was 0.4 and 3.8, respectively. Based on our previous work, the reverse‐micelles retain their aqueous core and are not altered during filtration. Ultimately, inorganic membrane separations can reduce energy consumption associated with compression/expansion cycles typically used in CO₂‐based processes.     

陶瓷膜微滤凹凸棒土过程中膜污染的控制和再生

采用阻力系列模型分析了膜污染主要来自凹土在膜表面的沉积,通过Darcy定律过滤模型计算,确定过滤过程的阻力主要来自滤饼层阻力Rg,约占总阻力的85%。实验结果表明,单一的物理、化学清洗方法不能达到理想的清洗效果,采用化学方法和反冲技术相结合的清洗方法,可使膜的纯水通量恢复至新膜的89 %以上,且多次的清洗效果稳定。考察了反冲压力、反冲时间和反冲周期等因素对陶瓷膜微滤凹土浆液强化过程的影响,确定合适的反冲操作条件：反冲压力0. 5 MPa、时间10 s、周期20 min。反冲技术在陶瓷膜微滤过程的膜污染控制和再生环节上起了重要作用,并具有广阔的应用前景。     

Effects of Nafion® Dehydration in PEM Fuel Cells

The current dependence of the ohmic resistance of Nafion membranes was examined with different types of humidification: cathodic (ChAd), anodic (CdAh), anodic and cathodic (ChAh) and no humidification at all (CdAd). Data show that for stacks with humidified cathodes (ChAd and ChAh), the resistance is small and relatively insensitive to the presence of the anodic humidification. On the contrary, for stacks with non-humidified cathodes (CdAh and CdAd), the membrane resistance is high and strongly dependent on current and anodic humidification. The kinetics of membrane dehydration was examined by recording the galvanostatic transients of the stack voltage and resistance, after removing the humidification. It was found that the changes in the ohmic resistance ΔR _Ω(t), although significant, cannot explain entirely the observed decay of the stack voltage. To account for the difference, an additional resistive term is introduced ΔR _p(t). Explicit equations were found for the time and current dependence of the two resistive terms ΔR _Ω(t) and ΔR _p(t) after humidification removal. A tentative explanation for the new resistive term was provided using electrochemical impedance spectroscopy (EIS). EIS data obtained at low overpotential show that dehydration of the Nafion present in the cathode catalytic layer results in an increase of the polarization resistance; the apparent deactivation of the cathode electrocatalyst appears to be due to a decrease of the electrochemically active surface area.     

Study of the separation of yeast by microsieves: In situ 3D characterization of the cake using confocal laser scanning microscopy

In situ 3D characterization of Aquamarijn microsieves fouling was achieved using Confocal Laser Scanning Microscopy (CLSM). A filtration chamber allowing direct microscopic observation of microbial cell deposition and cake characterization, specially designed for in situ observations, was used. Fluorescent dyed Saccharomyces cerevisiae yeast suspensions were filtered through 0.8 μm and 2 μm pore diameters silicon nitride microsieves under constant flow rate. The on-line yeasts deposition was recorded and the cake construction was followed layer by layer. Based on the 3D image processing, cake properties (particle arrangement, homogeneity, thickness and porosity). The compressibility of the yeast cake was analyzed. Finally, cake removal efficiency was also studied during microsieve cleaning operation.     

Crossflow Ultrafiltration of Binary Biomolecule Mixture: Analysis of Permeate Flux,Cake Resistance and Sieving Coefficient

The aim of this paper is to demonstrate the effects of hydrodynamic conditions on the permeate flux, cake resistance and sieving coefficient in a crossflow ultrafiltration process separating biomolecules of different molecular weights. A binary mixture of L‐phenylalanine (L‐phe) and lipase was ultrafiltered through a hydrophobic polyether sulphone (PES) membrane with 10 kDa molecular weight cut‐off. The changes in permeate flux, cake layer resistance and observed sieving coefficient with different transmembrane pressures (TMP) and crossflow velocities were evaluated. The effect of TMP was examined at two different velocities (0.114 m s^–1 and 0.176 m s^–1) and the effect of velocity was examined at two different TMP (20 kPa and 115 kPa) for the experimental system designed. In the initial stage of the crossflow filtration, it was determined that the TMP was more effective than the velocity. The cake layer resistance increased with increasing TMP and it decreased with increasing velocity for the high TMP value of 115 kPa. A maximum of the observed sieving coefficient was achieved with increasing velocity. An increase in TMP at low inlet velocity (0.114 m s^–1) affected the observed sieving coefficient positively.