Effect of PVP Molecular Weights on the Properties of PVDF-TiO2 Composite Membrane for Oily Wastewater Treatment Process

Polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membranes consisted of TiO₂ and different molecular weight (M_w) of polyvinylpyrrolidone (PVP) (i.e., 10, 24, 40, and 360 kDa) were prepared to treat synthesized oily wastewater. The membrane performances were characterized in terms of pure water flux, permeate flux, and oil rejection while their morphological properties were studied using SEM, AFM, and tensile tester. Results show that the PVDF-TiO₂ composite membrane prepared from PVP40k was the best performing membrane owing to its promising water flux (72.2 L/m².h) coupled with good rejection of oil (94%) when tested with 250 ppm oily solution under submerged condition. It is also found that with increasing PVP M_w, the membrane tended to exhibit higher PVP and protein rejection, greater mechanical strength, smaller porosity, and a smoother surface layer. Regarding the effect of pH, the permeate flux of the PVDF-PVP40k membrane was reported to increase with increasing pH from 4 to 7, followed by decrease when the pH was further increased to 10. Increasing oil concentration in the feed solution was reported to negatively affect the water flux of PVDF-PVP40k membrane, owing to the formation of thicker oil layer on the membrane surface which increased water transport resistance. A simple backflushing process on the other hand could retrieve approximately 60% of the membrane original flux without affecting the oil separation efficiency. Based on the findings, the PVDF-TiO₂ membrane prepared from PVP40k can be potentially considered for oily wastewater treatment process due to its good combination of permeability and selectivity and reasonably high water recovery rate.     

Performance evaluation of polyamide nanofiltration membranes for phosphorus removal process and their stability against strong acid/alkali solution

In this study,a quantitative performance of three commercial polyamide nanofiltration(NF) membranes(i.e.,NF,NF90,and NF270) for phosphorus removal under different feed conditions was investigated.The experiments were conducted at different feed phosphorus concentrations(2.5,5,10,and 15 mg·L~(-1)) and elevated pHs(pH 1.5,5,10,and 13.5) at a constant feed pressure of 1 MPa using a dead-end filtration cell.Membrane rejection against total phosphorus generally increased with increasing phosphorus concentration regardless of membrane type.In contrast,the permeate flux for all the membranes only decreased slightly with increasing phosphorus concentration.The results also showed that the phosphorus rejections improved while water flux remained almost unchanged with increasing feed solution pH.When the three membranes were exposed to strong pHs(pH 1.5 and 13.5) for a longer duration(up to 6 weeks)it was found that the rejection capability and water flux of the membranes remained very similar throughout the duration,except for NF membrane with marginal decrement in phosphorus rejection.Adsorption study also revealed that more phosphorus was adsorbed onto the membrane structure at alkaline conditions(pH 10 and 13.5) compared to the same membranes tested at lower pHs(pH 1.5 and 5).In eonelusion,NF270 membrane outperformed Nf and NF90 membranes owing to its desirable performance of water flux and phosphorus rejection particularly under strong alkali solution.The NF270 membrane achieved 14.0 L·m~(-2)·h~(-1) and 96.5% rejection against 10 mg·L~(-1) phosphorus solution with a pH value of 13.5 at the applied pressure of 1 MPa.     

Comparison of polyamide nanofiltration and low-pressure reverse osmosis membranes on As(III) rejection under various operational conditions

A nanofiltration (NF) membrane and a low-pressure reverse osmosis (LPRO) membrane both with aromatic polyamide selective layer from the same manufacturer were employed for the comparison of their performances in terms of As(III) rejection and filtration flux under a variety of operational conditions. In addition to the smaller membrane pore size, the LPRO membrane possesses much more dissociable functional groups than the NF membrane. When the feed pH was below the pKa₁ value (9.22) of H₃AsO₃, for which the steric hindrance is the only rejection mechanism, the removal efficiencies by NF and LPRO were about 10% and 65%, respectively. When the feed pH was higher, for which electrostatic effect began to take effect, the removal efficiencies could reach 40% and 90% for NF and LPRO, respectively. The rejection performance of LPRO was marginally affected by the feed As(III) concentration or ionic strength, although ionic strength had a strong effect on the filtration flux. In contrast, feed As(III) concentration and ionic strength had little effect on the filtration flux but great influence on the As(III) rejection performance of NF. The filtration flux was enhanced with the increase of transmembrane pressure for either NF or LPRO. The NF model could predict the general trend of the effects of the filtration flux, the feed water chemistry and its own concentration on As(III) rejection ratio by the NF membrane, but the rejection ratios were over-predicted.     

聚电解质静电沉积改性制备高性能反渗透膜

利用次氯酸钠溶液对商品反渗透膜表面进行氯化处理,然后将聚阳离子电解质壳聚糖通过静电吸附作用沉积在RO膜的表面,系统地研究了氯化过程的pH、氯化时间、次氯酸钠浓度、壳聚糖浓度及其沉积时间对膜性能的影响,以制备出高通量、高截留率的RO膜。在压力1.55 MPa、原料液温度（298±1）K的条件下,测定RO膜处理2000 μg·g^-1氯化钠溶液的水通量和截留率。结果表明,当pH=9、氯化时间为30 min、次氯酸钠浓度为1000 mg·L^-1时,水通量较原膜提高了约19.89%,截留率略有提高;当壳聚糖浓度为0.1%（质量分数）、沉积时间为30 min时,改性膜的接触角降低到34.88°,亲水性提高,水通量较氯化后的RO膜几乎保持不变,为60.55 L·m^-2·h^-1,截留率达到了99.56%。经过氯化和沉积改性后的RO膜水通量和截留率均得到了提高。     

反渗透、纳滤过程的物理化学研究（Ⅱ） 多孔荷电膜的溶质分离规律

在多孔膜溶质的脱除率方程和溶液渗透通量方程的基础上由溶液电中性条件导出了荷电膜的单价电解质、中性分子混合溶液体系离子的脱除率方程,中性分子的脱除率方程,溶液渗透体积通量方程和离子、中性分子的浓缩比表达式。由方程的函数性质讨论了荷电膜的单价电解质、中性分子混合溶液的溶质组分脱除率和溶液渗透体积通量随离子浓度、pH值的变化规律。预测了盐和中性分子的脱除率和溶液渗透体积通量随浓度变化曲线出现极大和极小值的现象,由此得出了下列结果：随pH值的增加,单价电解质溶液的阳离子、阴离子和氢离子的脱除率变化顺序为由 R _M⁺ > R _X^- > R _H⁺变化到R _M⁺ =R _X^-> R _H⁺再变化到R _X^->R _M⁺> R _H⁺,离子脱除率变化曲线将出现极大和极小值;有机酸的总脱除率表达式阐明了文献中的可电离有机分子与pH值的关系式中参数的物理意义,解释了该关系式的对氨基苯甲酸水溶液的脱除率随pH值变化的拟合曲线高于脱除率实验值的原因,解释了对氨基苯甲酸的甲醇溶液的溶质脱除规律;离子的浓缩比依赖于料液中离子组成和离子所对应盐的浓缩比。     

Effect of different operating parameters on the recovery of proteins from casein whey using a rotating disc membrane ultrafiltration cell

In this study, effects of different operating parameters in ultrafiltration (UF) of casein whey in rotating disk ultrafiltration module, fitted with a 30 kD followed by a 5 kD molecular weight cut-off (MWCO) membrane have been analyzed and the benefits of membrane rotation with respect to stationary membrane module are highlighted. Prior to UF, centrifugation and microfiltration (MF) were carried out with the raw casein whey with an aim to remove the major membrane foulants like colloidal matters, suspended casein particles and lipid. The effects of pH, membrane rotation and transmembrane pressure (TMP) on UF flux and rejection were studied thoroughly, giving an emphasis on the effect of operating conditions in pressure and mass transfer controlled region as well. It was observed that solution pH was having a strong effect on UF flux and rejection for treating casein whey, which was explained in terms of prevailing monomer-dimer equilibrium of β-lactoglobulin, a major constituent of casein whey, as well as due to conformational changes of protein molecules with respect to isoelectric point. It was observed that for the 30 kD membrane, after 20 min of operation, 28.5% higher flux was obtained at pH 2.8 compared to pH 5.5 at a pressure of 490 kPa for stationary membrane, whereas the same figure for rotating membrane was 49.5%. Further, 38.7% higher UF flux at 300 rpm membrane speed compared to stationary membrane in 20 min of operation at pH 2.8 and TMP 490 kPa suggests the importance of shear across the membrane in minimizing the effects of concentration polarization. In the 5 kD membrane α-lactalbumin, which was mainly in the permeate stream from the 30 kD membrane, was separated from the other low molecular weight component of whey, such as lactose.     

Ultrafiltration behavior in the treatment of agro-industry effluent: Pilot scale studies

This pilot-scale study deals with highly polluting agro-industry's wastewater, palm oil mill effluent (POME). Ceramic ultrafiltration membrane was applied to treat this effluent. UF separation behavior of POME is reported. The effects of transmembrane pressure and crossflow velocity on permeate flux, limiting flux and percentage rejection for suspended solids and dissolved organic matters were investigated. The limiting flux obtained was further applied to determine critical flux and deposit resistance, R_c, using the possible theoretical link of critical flux and limiting flux. The verified values of critical flux are useful in the operation of ultrafiltration to minimized membrane fouling; thus, longer lifespan of the membrane can be expected. Both transmembrane pressure and crossflow velocity show their significant effects to the permeate flux, whereas only the crossflow velocity influences the rejection of dissolved organic matters in terms of COD and BOD.     

Boron removal from seawater using high rejection SWRO membranes — impact of pH, feed concentration, pressure, and cross-flow velocity

The main objective of this work was to investigate boron removal from seawater using two commercial high rejection SWRO membranes. The impact of solution pH, feed concentration, pressure, and cross-flow velocity on boron rejection and permeate flux was determined. The membranes used were the Toray™ UTC-80-AB and Filmtec™ SW30HR. A lab-scale cross-flow flat-sheet configuration test unit was used for all RO experiments. Seawater sample was collected from the Mediterranean Sea, Alanya-Kızılot shores, south Turkey. For all experiments, mass balances were between 91% and 107%, suggesting relatively low loss of boron on membrane surfaces during 14 h of operation. Operation modes did not have any impact on boron rejection, indicating that boron rejection were independent of feedwater boron concentrations up to 6.6 mg/L. For both membranes, much higher boron rejection were obtained at pH of 10.5 (>98%) than those at original seawater pH of 8.2 (about 85–90%). Permeate boron concentrations less than 0.1 mg/L were easily achieved at pH 10.5 by both membranes. The dissociated boron species are dominant at this pH, thus both electrostatic repulsion and size exclusion mechanisms are responsible for the higher boron rejection. The rejection of salts in seawater did not correlate with boron rejection at constant conditions. For each membrane type, permeate fluxes at constant pressure were generally lower at pH of 10.5, which may be partially explained by membrane fouling and enhanced scale formation by Mg and Ca compounds from concentration polarization effect at higher pH values. While somewhat higher boron rejection was found for one membrane type as the pressure was increased from 600 to 800 psi, increasing pressure did not affect boron rejection for the other membrane. Feed flowrate thus the cross-flow velocity (0.5–1.0 m/s) did not exert any significant impact on boron rejection at constant conditions.     

操作条件对γ-Al2O3膜分离性能的影响

通过正交实验探讨了酸性条件下,温度、压力、PH值、流速、浓度对γ-Al2O3管式多孔膜渗透通量和Mg2+的截留率的影响。实验采用溶胶–凝胶法自制管式纳米孔膜和错流循环过滤方式。结果表明,操作压力和温度对膜通量的影响显著,同时压力及pH对截留率影响显著,而酸性环境下有利于γ-Al2O3多孔膜对阳离子的脱除。     

商业正渗透膜的改性及其用于处理焦化废水的研究

正渗透技术是一种新兴的膜分离技术,在处理有机废水方面具有广阔的应用前景。分别对Poten以及HTI商业正渗透膜进行改性,并用于对焦化废水中难降解毒性小分子(吲哚和吡啶)的截留测试。探究了水相单体PIP浓度、膜朝向、汲取液浓度对改性前后两种膜水通量、J_s/J_w比值、有机物截留率的影响,以及改性前后两膜特征参数的变化。结果表明：对Poten膜和HTI膜进行界面聚合改性后,膜水通量以及J_s/J_w比值都不同程度地降低;改性后的两正渗透膜水渗透系数A、盐渗透系数B均降低,而膜结构参数S以及对NaCl和有机物的截留率均提高;其中HTI-IP复合膜对有机物的截留率(81%)明显高于IP-2(改性Poten膜)复合膜;与FO模式相比,IP-2复合膜在PRO模式下(汲取液面向活性层)具有更高的水通量及反向盐通量。此外,在两种膜朝向下,水通量及反向盐通量都随汲取液浓度的增大而增大,但是在FO模式下(料液面向活性层),通量呈现非线性增长。     

Treatment of Oily Wastewaters Using the Microfiltration Process: Effect of Operating Parameters and Membrane Fouling Study

This work focuses on the treatment of oily wastewater using the cross-flow microfiltration (MF) process to determine the effect of different operating parameters such as transmembrane pressure (TMP) and cross-flow velocity on the separation performance and to study the mechanism of membrane fouling during microfiltration of oil in water emulsions. In this regard, the permeation flux and oil rejection of a polyvinylidene fluoride (PVDF) membrane in a flat-frame MF module for separation of 3000 ppm oil/water emulsions were measured. The results indicated that the permeate flux increased by an enhancement in both TMP and cross-flow velocity, while the oil rejection decreased. The analysis of variance (ANOVA) showed that the individual effect of TMP and cross-flow velocity is more important than the interactional effect of these operating parameters on the permeate flux and oil rejection. The results of fouling modeling revealed that the membrane fouling mechanism was affected by the applied TMP. The cake filtration model dominates the fouling mechanism at lower operating pressures. The fouling mechanism was changed from the cake formation to intermediate pore blocking and then to standard pore blocking as the TMP varied from 1 to 3 bar. Finally, a five-step procedure was used for cleaning the oil/water fouled membranes.     

Separation of nickel catalyst by microfiltration

Ceramic membranes with pore size of 0.1 and 0.2 µm are used for the separation of nickel catalyst. Effect of trans‐membrane pressure (TMP), linear velocity, temperature and nickel content (solute) on flux and rejection has been investigated. The flux increased with increase in pore size of the membrane. The rejection characteristics were similar for 0.1 and 0.2 µm membranes. The nickel content and iodine value of the membrane‐filtered oil was comparable with that of conventional processes. Permeate flux increased with increase in temperature. Flux increased with increase in linear velocity and a marginal rise was observed above 2.09 m/s. The rejection characteristics were only slightly affected by higher linear velocity. The flux improved after back flushing. The average flux was higher with back flushing as compared to continuous (with out back flushing) filtration process. The results indicated that the secondary layer effect was more pronounced in microfiltration. The flux decreased with increase in solute concentration. The rejection characteristics were not affected by solute concentration. The rejection characteristic of the membranes remained unaltered after membranes were repeatedly cleaned with sodium hydroxide and HCl solutions, however, the flux was decreased marginally.     

纳滤法处理含氟废水工艺条件的研究

采用Dow FilmTec公司的NF-90纳滤膜处理模拟含氟废水,主要考察了压力、pH、流量、温度、氟离子初始浓度等对膜渗透通量和氟离子截留率的影响。结果表明:压力升高,膜渗透通量增大,氟离子截留率先增大后减小;pH对膜渗透通量无明显影响,氟离子截留率随pH的升高而增大;流量升高膜渗透通量和氟离子截留率略有增大;温度升高,膜渗透通量增大,氟离子截留率降低;氟离子初始浓度增大,膜渗透通量减小,氟离子截留率降低。在压力1.0 MPa、pH 10.01、流量30 L/h、温度20℃的条件下NF-90膜截留率可达到95%;当处理氟浓度小于100 mg/L,出水氟浓度可达到国家工业一级排放标准。     

溶液pH值对微纳米气泡减轻超滤膜污染影响研究

为有效解决膜过滤过程中由于膜污染加剧而导致分离效率下降的问题,提出引入微纳米气泡工艺,研究了pH值为3.0、6.0和10.0时微纳米气泡(MNBs)对超滤过程的影响,通过扫描电镜和聚焦离子束电子束双束显微镜分析了膜表面污染。实验结果表明pH值为3.0、6.0和10.0时鼓入MNBs后超滤归一化通量分别为0.96、1.19和1.14。pH值为3.0时鼓入MNBs对腐植酸(HA)截留率无明显增强,pH值为6.0和10.0时鼓入MNBs后截留率分别提高了12.7%和10.0%。超滤膜表面滤饼层厚度随pH值增大而减小,鼓入MNBs后滤饼层疏松多孔,有效减弱了归一化通量下降。     

Sugar Purification from Enzymatic Rice Straw Hydrolysis Products using Cross-Flow Diafiltration

The sugars produced by enzymatic hydrolysis of rice straw are separated using cross-flow diafiltration in this study. The effects of membrane type, membrane pore size, cross-flow velocity and transmembrane pressure on the filtration flux, sugar rejection, and sugar mass flux transported to the filtrate are discussed. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. When the membrane made of mixed cellulose ester (MCE) is used, over 70% filtration resistances are caused by the membrane fouling; while the resistance due to virgin membrane is dominant when regenerated cellulose (RC) membranes are used. A force balance model is applied to relate the filtration flux and filtration resistance to operating conditions. The calculated data of filtration flux based on this model agree fairly well with experimental data. In addition, a theoretical model is used to explain the sugar transmission through the cake and membrane pores. The sugar rejection coefficient decreases with increasing cross-flow velocity because of the effect of cake reduction. This effect is more significant when the MCE membrane is used. Comparing the sugar mass flux transported into the filtrate, it is more effective for sugar purification by using 10 kD RC membrane and under higher transmembrane pressures.     

Plasma Polymerization Modified Polyvinylidene Fluoride (PVDF) Membrane Development and Characterization for Degumming of Soybean Oil

Unmodified and surface‐modified polyvinylidene fluoride (PVDF) membranes were tested for their ability to degum soybean crude oil and crude oil miscellas. The membrane was modified with 1,1,1,3,3,3‐hexafluoro‐2‐propanol or hexamethyldisiloxane (HMDSO) by radio‐frequency plasma polymerization at 10–100 W glow discharge power and 1–30 min contact time. The membranes were characterized by contact angle measurements, attenuated total reflectance Fourier transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. Modification of the PVDF membrane with HMDSO at 60 W power for 5 min increased the interfacial free energy between water and solid surface from 30 ± 2 to 64 ± 2 mJ/m². This membrane was tested for permeate flux and phospholipid rejection with crude oil and different concentrations of miscella. Although formation of the polymer film on the membrane tended to decrease membrane pore size, the modified membrane had an oil flux as good as the unmodified membrane did. In addition, the modified‐membrane improved the phospholipid rejection and removed 76 % of the phospholipids from the crude oil and 81–90 % of the phospholipids from crude oil miscellas.     

Separation of oil constituents in organic solvents using polymeric membranes

Different types of commercial nonporous (reverse osmosis and gas separation) polymeric membranes were screened for their abilities to separate FFA, MG, DG, and TG from a lipase hydrolysate of high-oleic sunflower oil after diluting it with organic solvents (ethanol and hexane). Cellulose acetate (CA) (NIR-1698) membrane gave the largest difference in rejection between FFA and glycerides and high flux in oil/ethanol mixtures. In the hexane system, the values of permeate flux and rejection were generally lower than those in the ethanol system. The silicone-polyimide composite membrane (NTGS-2100) gave the highest flux and rejections of solutes (70.2% for FFA, 94.4% for TG) in oil/hexane mixtures. In the ethanol system with the CA membrane, TG had the highest rejection (98%) followed by DG (90%) and MG and FFA (50–70%) when the oil concentration was varied from 6.3 to 45.8%. A discontinuous diafiltration process (16 batches) using the CA membrane with ethanol changed the composition of the oil from 31∶28∶9∶32 TG/DG/MG/FFA to 65∶30∶1∶4. The results of this study showed that oil constituents can be separated in suitable solvents using appropriate nonporous membranes.     

纳米ZrO2修饰Al2O3微滤膜处理废冷却液的实验研究

膜分离技术处理含油废水表现出明显的技术优势,其应用还应解决膜表面易被污染,分离效果逐渐下降的问题,主要原因是由于油滴的易变形性引起的膜堵塞。为解决膜渗透通量与膜选择性的矛盾,本文在市售Al2O3微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,阻止油滴的变形。研究了陶瓷膜修饰条件和膜过滤操作参数对膜渗透通量的影响,结果表明:纳米涂层能有效提高微滤膜的渗透通量。膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显。当膜面流速为7m/s,修饰陶瓷膜的最大渗透通量为280 L.m-2.h-1,油截留率为96.4%。纳米涂层修饰微滤膜具有良好的抗油滴污染性能,能有效实现稳定含油废水的油水分离。     

Concentration of gelatin solution with polyethersulfone ultrafiltration membranes

In this work, polyethersulfone (PES) flat sheet ultrafiltration (UF) membranes were prepared by immersion precipitation phase inversion process with polyvinylpyrrolidone (PVP 30K) and acetone as additives. The best preparation condition for PES membranes with high water flux and rejection (to BSA) was decided. It was found that the optimal composition of the polymer casting solution was: 16 wt% (PES), 2 wt% (PVP 30K), and 1 wt% (acetone). Pure water flux of the membrane prepared at this condition reached to 373 L/m² h at 0.1 MPa, and the rejection to BSA was 91%. Compared with other reports, the rejection was slightly low but the flux of the PES membrane was high. When the membrane was used to concentrate gelatin solutions, the rejection value was over 75%. It was found that increasing the feed temperature and transmembrane pressure enhanced the permeation flux, but the rejection decreased slightly. However, increasing the cross-flow velocity of the feed solution simultaneously increased both the permeation flux and the rejection.     

Synthesis and characterization of superoleophobic fumed alumina nanocomposite coated via the sol-gel process onto ceramic-based hollow fibre membrane for oil-water separation

Oily wastewater treatment is a global challenge due to the substantial amount of effluent resulted from many industrial and domestic activities. To overcome the challenge of using existing treatment approach and fouling, superoleophobic coatings were fabricated. In this study, a superoleophobic membrane surface was obtained using the sol-gel technique with perfluorooctanoate (PFO), poly (diallyl dimethylammonium chloride) (PDADMAC), and nanoparticles as complex-polymer nanocomposites. The effects of coating cycles on the surface structure, chemical properties, surface chemistry, and oleophobicity of the surface were examined using field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and oil contact angle measurement. The results showed that the coated layer successfully adhered to the substrate surface. However, the chemical stability with respect to oil contact angle (OCA) revealed a decline at pH 7 and pH 9 and maintained stability at pH 3. Besides, oil flux at 63.0 L/m². h was achieved for PDADMAC-Al₂O₃/44 wt% PFO and the highest separation efficiency of 98% was obtained. Furthermore, the oil rejection decreases as the oil concentration increases from 1 to 3 g/L. OCA of 155° was obtained after 5 coating cycles. Apart from mitigating substrate fouling, the superoleophobic and superhydrophilic coating can be applied to a ceramic-based hollow fibre membrane and efficiently used for the separation of oil from oily wastewater.