Clarification of red raspberry juice using microfiltration with gas backwashing: A viable strategy to maximize permeate flux and minimize a loss of anthocyanins

Red raspberry (Rubus idaeus) juice was produced by maceration of raspberry pulp at 50 °C for 2 h using 400 mg kg^?1 Klerzyme^®150 enzymatic pectolitic preparation followed by raw juice clarification with gelatin and bentonite or cross-flow membrane filtration. A minimal loss of anthocyanins from 630 to 540 mg l^?1 was obtained when the juice was clarified using a ceramic multichannel microfilter (MF) with a pore size of 0.2 μm. A light transmission at 625 nm in MF permeate was above 85% and the residual pectin (900 mg l^?1) was completely removed. During ultrafiltration through ceramic or polysulfone membranes with a molecular weight cut-off of 30–300 kDa, the content of anthocyanins was reduced to 220–370 mg l^?1, but a light transmission at 625 nm was as high as 96%. The permeate flux in MF was maintained at high values above 170 l m^?2 h^?1 at 3 bar for more than 2 h by backwashing the membrane with a compressed air every 6 min for 1 min. The cake compression at high pressures was avoided by short filtration times between backwashing.     

Fouling control in sugarcane juice ultrafiltration with surface modified polysulfone and polyethersulfone membranes

Commercial 50 and 100 kD polyethersulfone (PES) and polysulfone (PS) ultrafiltration membranes were surface modified by UV photografting of poly(ethylene glycol) methacrylate (PEGMA) monomer. The modified membranes were characterized by the degree of grafting, water flux and molecular weight cutoff (MWCO) rating. The flux and fouling of the modified and unmodified membranes were examined with sugarcane juice and its polysaccharide fraction. Under the conditions of this study, the modified membranes displayed a low degree of grafting (26-36 μg/cm²), which was independent of the UV exposure duration; however, both membrane water flux and MWCO rating were affected by the irradiation time. In the best case, the modified membranes exhibited lower fouling with sugarcane juice; furthermore, the propensity to foul also decreased. More significantly, juice flux recovery was almost complete for successive UF-cleaning cycles.     

Fabrication and characterization of hydrophobic PVDF hollow fiber membranes for desalination through direct contact membrane distillation

The mixture of inorganic salt LiCl and soluble polymer polyethylene glycol (PEG) 1500 as non-solvent additive was introduced to fabricate hydrophobic hollow fiber membrane of polyvinylidene fluoride (PVDF) by phase inversion process, using N,N-dimethylacetamide (DMAc) as solvent and tap water as the coagulation medium. Compared with other three membranes from PVDF/DMAc, PVDF/DMAc/LiCl and PVDF/DMAc/PEG 1500 dope solution, it can be observed obviously by scanning electron microscope (SEM) that the membrane spun from PVDF/DMAc/LiCl/PEG 1500 dope had longer finger-like cavities, ultra-thin skins, narrow pore size distribution and porous network sponge-like structure owing to the synergistic effect of LiCl and PEG 1500. Besides, the membrane also exhibited high porosity and good hydrophobicity. During the desalination process of 3.5 wt% sodium chloride solution through direct contact membrane distillation (DCMD), the permeate flux achieved 40.5 kg/m² h and the rejection of NaCl maintained 99.99% with the feed solution at 81.8 °C and the cold distillate water at 20.0 °C, this performance is comparable or even higher than most of the previous reports. Furthermore, a 200 h continuously desalination experiment showed that the membrane had stable permeate flux and solute rejection, indicating that the as-spun PVDF hollow fiber membrane may be of great potential to be utilized in the DCMD process.     

Modeling of turbulent cross flow microfiltration of pomegranate juice using hollow fiber membranes

A mathematical analysis of the permeate flux decline during microfiltration of fruit juice with hollow fibers under turbulent flow is presented. Impact of complex fluid flow phenomena on mass transfer is analyzed. A comprehensive analytical model for developing concentration boundary layer was formulated from first principles using integral method. Attempts to model the system considering constant boundary layer thickness (film theory) is inaccurate for developing boundary layer. Gel resistance parameter depending on juice characteristics has significant impact on permeate flux. Specific gel layer concentration has insignificant effect on system performance under total recycle mode but important for batch mode. Theoretical results were compared with experiments in clarification of pomegranate juice with poly(ether ether ketone) and polysulfone hollow fiber membranes. The physical parameters of complex mixture were evaluated by optimizing of the flux profiles in total recycle mode of operation and were successfully applied for prediction of batch mode performance. © 2014 American Institute of Chemical Engineers AIChE J 60: 4279–4291, 2014     

Huangpu River water treatment by microfiltration with ozone pretreatment

With the promulgation of more stringent regulations to guarantee the quality of drinking water, low pressure membrane processes are nowadays considered for surface water treatment. But these membranes are sensitive to fouling. In this study ozone is introduced to pretreatment for membrane filtration to get a high quality permeate and improve membrane performance. The organic matter characteristics, such as AMWD of organic matter, hydrophilic/hydrophobic fractions were studied with ozone oxidation. Results show that for Huangpu River water, ozone oxidation offers high percentage of UV absorbance removal than DOC removal. Highest removal of DOC and UV₂₅₄ of 10% and 71% respectively were observed. The dominant organic matter oxidized by ozone was 2-7.0 kDa in terms of molecule distribution investigation. Ozone oxidizes more hydrophobic fraction to hydrophilic one. Changes of organic matter composition improved membrane flux. There is the optimal dosage with ozone of 1.5 mgO₃/L made membrane flux maximum during 0.5-3.0 mgO₃/L ozone dosage. Ozone oxidization provided degradation of macromolecule organic matter, which is responsible to membrane fouling, to small molecule organic substance. Study about the chemical cleaning of the fouled membrane also supports the point that membrane fouling is produced by the organic substance with high molecule weight.     

Physico-chemical parameters of cactus pear (Opuntia ficus-indica) juice clarified by microfiltration and ultrafiltration processes

The health-promoting capacity of cactus pear fruit is highly attractive for the development of nutraceutical foods. The increasing market demand towards this fruit and products, which combine added value with a fresher taste, has challenged researchers to develop procedures to lengthen storage life. In addition, the possibility to obtain natural colorants from the cactus pear fruit rather than synthetic colorants for drinks and dairy products represents another interesting perspective.In this study the effect of microfiltration (MF) and ultrafiltration (UF) processes on the physico-chemical composition of the cactus pear juice produced from fruits of Italian (Sicily) origin was investigated in order to evaluate the influence of the clarification treatment on the content of main parameters characterising the nutritional and functional properties of the fruit. Effects of operating parameters on the performance of both processes in terms of permeate fluxes were also evaluated.     

Controlled grafting from poly(vinylidene fluoride) microfiltration membranes via reverse atom transfer radical polymerization and antifouling properties

A reverse atom transfer radical polymerization (RATRP) with benzoyl peroxide (BPO)/CuCl/2,2-bipyridine (Bpy) was applied onto grafting of poly(methyl methacrylate) (PMMA) and poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) from poly(vinylidene fluoride) (PVDF) microfiltration (MF) membrane surfaces, including the pore surfaces. The introduction of peroxide and hydroperoxide groups onto the PVDF membranes was achieved by ultraviolet (UV) irradiation in nitrogen, followed by air exposure. RATRP from UV pretreated hydrophobic PVDF membranes was then performed for attaching well-defined homopolymer. The chemical composition of the modified PVDF membrane surfaces was characterized by attenuated total reflectance (ATR) FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface and cross-section morphology of membranes were studied by scanning electron microscopy (SEM). The pore sizes of the pristine PVDF and the PMMA grafted PVDF membranes were measured using micro-image analysis and process software. With increase of graft concentration, the pore size of the modified membranes decreased and became uniform. Kinetic studies of homogeneous (in toluene solution) system revealed a linear increase in molecular weight with the reaction time and narrow molecular weight distribution, indicating that the chain growth from the membrane surface was a “controlled” or “living” grafting process. The introduction of the well-defined PMMA on the PVDF membrane gave rise to hydrophilicity. Protein adsorption and protein solution permeation experiments revealed that the UV pretreated hydrophobic PVDF membrane subjected to surface-initiated RATRP of methyl methacrylate (MMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) exhibited good antifouling property.     

拉伸流动场诱导PVDF/BaTiO3流延膜结晶行为研究

利用挤出流延过程中的拉伸应力场对聚偏氟乙烯/钛酸钡(PVDF/BaTiO3)复合材料进行原位非等温拉伸试验,研究了拉伸比及BaTiO3用量对PVDF/BaTiO3流延膜结晶结构和介电性能的影响。广角X射线衍射结果表明,PVDF/BaTiO3复合膜的取向程度明显大于纯PVDF。X射线小角衍射结果显示:对于纯PVDF,第二个散射峰的强度随拉伸的进行而不断提高,在拉伸比为1.5时,其强度明显超过第一个散射峰;加入BaTiO3后,第一个散射峰的强度比纯PVDF明显提高,而第二个散射峰的强度也随拉伸比的提高而增强。复合膜的组成相同时,其介电常数随拉伸比的提高而减小,而介电损耗随拉伸比的提高而增大。     

Removal of iron and manganese from groundwater by oxidation and microfiltration

Iron and manganese can be removed from groundwater by a process which combines oxidation and microfiltration (MF), especially when the concentrations of these metals are high and variable. The present experimental work focused on the MF of iron and manganese oxide suspensions in order to study the effects of the operating variables (tangential flow rate, pressure, metal feed concentrations) on permeate quality and permeation flux decline, i.e., membrane fouling. Artificial and natural groundwaters in which iron and manganese were previously oxidized were used to perform laboratory-scale MF experiments. The results show that the oxide particles, with sizes ranging from 1.5 to 50μm, were efficiently microfiltered even at high concentrations. Within the experimental limits, the effect of operating pressure appeared to be much more significant than the those of tangential flow rate and feed concentration. A relatively high and constant permeation rate of 0.5 m/h was obtained at a pressure below 10 kPa, whereas rapid permeation flux declines were observed at higher pressure. Both artificial and natural groundwaters always exhibited very similar behavior.     

改性PVDF膜抗污染性进展探究

聚偏氟乙烯以其优异的力学性质和化学性质在膜分离技术中被广泛应用,其表面的极强疏水性,导致在水处理过程中极易受到污染且恢复率很低。所以膜的改善亲水性具有十分重要的意义。根据不同的改性粒子分类,结合主要的改性方法,将国内外近几年对PVDF改性效果较好的纳米粒子和两亲性共聚物进行综述和性能对比,着重从渗透性和抗污性比较了各种粒子的改性效果。最后对PVDF膜亲水性改善进行总结和展望。     

New ceramic microfiltration membranes from Tunisian natural materials: Application for the cuttlefish effluents treatment

New microfiltration membranes from Tunisian natural materials are obtained using ceramic method. Paste from Tunisian silty marls refereed (M₁₁) is extruded to elaborate a porous tubular configuration used as supports. The support heated at 1190 °C, shows an average pore diameters and porosity of about 9.2 μm and 49%, respectively. The properties in term of mechanical and corrosion resistances are very interesting. The elaboration of the layer based on Tunisian clay refereed (JM₁₈) is performed by slip-casting method. The heating treatment at 900 °C leads to an average pore size of 0.18 μm. The water permeability determined of this membrane is 867 l h⁻¹ m⁻² bar⁻¹. This membrane can be used for crossflow microfiltration. The application to the cuttlefish effluent clarification shows an important decrease of turbidity (inferior to 1 NTU) and chemical organic demand (COD) values (retention rate of about 65%). So, it seems that the prepared membrane is suitable for such wastewater treatment.     

Removal of phenol and phosphoric acid from wastewater by microfiltration carbon membranes

Microfiltration carbon membranes were developed to cope with the wastewater containing phenol and phosphoric acid. The structure of carbon membranes was characterized by scanning electron microscope, x-ray diffraction, bubble pressure method and specific surface area analysis. The separation efficiency of carbon membranes was investigated by varying the operation factors, including feed concentration, running time, and pressure. Results have shown that the carbon membranes are abundant in porous structure with the porosity of 42%, along with a narrow pore size distribution centering at 0.18?µm. Within the scope of the study, the highest removal rates reach to 81.9% for phenol and 55.3% for phosphoric acid from wastewater, respectively.     

The effects of molecular weight and polymorphism on the fracture and thermo-mechanical properties of a carbon-fibre composite modified by electrospun poly (vinylidene fluoride) membranes

The interlaminar toughening of a carbon-fibre reinforced composite by incorporation of electrospun polyvinylidene fluoride (PVDF) nanofibrous membranes was explored in this work. The electrospinning process of low and high molecular weight PVDF was optimised to form nanofibres free of defects with diameters averaging several hundred nanometres. The nanofibres were electrospun directly onto commercial pre-impregnated carbon fibre materials and under these optimised conditions, PVDF primarily crystallised in its β phase polymorphic form but significant variations were observed between samples. There is strong evidence from DMTA analysis to suggest that a partial miscibility between the amorphous phases of the PVDF nanofibres and the epoxy exists. The improved plastic deformation at the crack tip after inclusion of the nanofibres was directly translated to a 57% increase in the mode II interlaminar fracture toughness (in-plane shear failure). Conversely, the fracture toughness in mode I (opening failure) was slightly lower than the reference by approximately 20%, and the results were interpreted from the complex micromechanisms of failure arising from the changes in polymorphism and molecular weight of the PVDF.     

Performance of a new ceramic microfiltration membrane based on kaolin in textile industry wastewater treatment

A ceramic microfiltration membrane with a porosity of 40.2%, mean pore diameter of 0.27?μm, and a flexural strength of 55?MPa was prepared and applied for treatment of two types of textile dye-bath effluents. The ceramic membrane had a water permeability of 1376?L/m².h.bar and showed excellent corrosion resistance against basic medium. Considerable removal of COD (25%), TDS (31%), BOD (39%), turbidity (21%), sulphates (34%), chlorides (33%), and color (26%) from textile effluents was achieved in the microfiltration treatment along with complete (100%) removal of TSS. This study revealed that filtration of textile effluents using a sub-micron range ceramic membrane (0.27?μm) is more effective than traditional microfiltration membranes (2–10?μm). The flux data fitted well with the standard pore blocking model indicating that the removal of various contaminants is due to adsorption of solutes on the interior surfaces of membrane pores.     

载体对Al_2O_3微滤膜的影响

采用浸浆法在α氧化铝载体上制备氧化铝微滤膜,研究了载体的润湿性能、表面的粗糙度、孔的大小及载体与膜的匹配等情况对微滤膜完整性的影响。结果表明,当载体表面光滑、润湿性能良好和载体的孔径大小与悬浮粒子大小和性能之间相匹配时,才能制得表面连续、完整的氧化铝微滤膜。     

Effect of nano-ZnO with different particle size on the performance of PVDF composite membrane

To evaluate the effect of nanoparticle size on the structure and performance of the membranes, polyvinylidene fluoride composite membranes modified by nano-ZnO with different particle size were successfully fabricated by the non-solvent induced phase inversion method. A series of tests, including contact angle measurement, porosity and pore size measurement, scanning electron microscope, atomic force microscopy, differential scanning calorimeter and filtration experiments were performed to characterise the composite membranes. The results showed that the size of nano-ZnO particle has an influence on the structure and performance of the composite membranes. The membrane with 90?nm nano-ZnO particle has abundant porosity, high hydrophilicity and low surface roughness. These features are responsible for its excellent permeability and antifouling property.     

Characterization of membrane distillation membranes prepared by phase inversion

In this paper, flat membrane distillation membranes have been successfully manufactured from PVDF/DMAc and PVDF/DMF blends by using phase inversion induced by an immersion precipitation technique. The structure of the membranes is asymmetric with a porous top layer and macrovoids, as assessed by SEM. The existence of MD fluxes in these membranes is established by performing various pure water flux experiments. A maximum in the MD fluxes for a particular value of the polymer content in the casting solution from which the membrane is manufactured has been observed. The dependence of the magnitude of the fluxes on the membrane thickness is also discussed and the influence of temperature polarization evaluated.     

附加湍流器强化陶瓷膜微滤过程的研究

通过在管式陶瓷膜内设置不同结构形式的湍流器，试验和比较了不同主体流速和膜滤压差等工艺条件下的膜滤速率及能耗，分析了湍流器所产生的强化膜滤过程的效果以及试验条件下的一般规律。     

Chemical cleaning of reverse osmosis membranes fouled by whey

The aim of this research was to establish a rationale for the cleaning of reverse osmosis (RO) membranes fouled by whey. Wheywas processed using a hydrophilic polyamide FT30 RO membrane. The effects ofoperating conditions such as transmembrane pressure, temperature and cross-flow velocity on flux behavior were elucidated before studying the cleaning. A wide variety of cleaning agents including acids, bases, enzymes and complexing agents was used. Resistance removal and flux recovery were used for demonstrating the cleaning efficiency. Hydrochloric acid (0.05 w%) resulted in maximum flux recovery and complete resistance removal. Although sodium hydroxide showed high cleaning efficiency, it may damage the membrane, predominantly at a high pH. Nitric acid and ammonia showed high but not complete resistant removal. Other acids (phosphoric acid and oxalic acid), ammonium chloride, urea and surfactants (SDS, Triton-X100 and CTAB) exhibited moderate effects while EDTA was of low efficiency. The cleaning effectiveness depends on the cleaner concentration. Using sulphuric acid, higher concentration caused lower resistance removal. For HCl the cleaning efficiency increased with the cleaner concentration, passed a maximum and decreased afterwards. Operating conditions such as cleaningtime and temperature affect cleaning efficacy. A longertime and higher temperature provide higher resistance removal. However, the effects are somewhat limited.